By Russ Sadler
Introduction
This technically is a video diary of my mistakes and successes as I gradually come to terms with the mysteries of owning one of these little Chinese dragons {Russ’s videos are also considered to be some of the best “How to use a laser cutter videos” on the web}. It seems illogical that a diary should have an index. That is something done by historians (after my passing) who have too much time on their hands waiting for history to happen!!!
However, after being put into a psychological headlock, I have relented and with the help of Gene Uselman who has carefully created the skeleton of this index, I have added pertinent bullet points to each video to help others find elements of interest.
This bullet point index has been made a year into my learning journey when I am older and wiser. It must be remembered at all times that this is a video record of me learning about a technology that is very poorly documented and, in my naivety, I make (what I can now see as) lots of silly mistakes. Where it is appropriate, I warn of my error BUT in the spirit of leaving the work as an unedited record of discovery I leave you to watch ahead to that point where I begin to realize and correct those errors
Thanks for your interest.
Russ July 2016
Table of Contents
RDWorks Learning Lab 151 ~ 200
151 Let’s Zoom in on Lenses Part 3
- Choosing a suitably demanding test material to cut
- The lenses that I have for all of these tests are 38.1mm focal length
- Selecting 10mm plywood (albeit soft poplar) seems an unreasonable demand for a 38mm lens.
- Let’s step back and look at my theory of woodcutting.
- A slow motion look at an unfocused beam pulse hitting the surface of wood.
- Yet again I go through the way light energy gets transferred to heat energy and causes the carbon in wood to sublimate into gas at 3,500C
- Demonstration (in slow motion) of a pulse burning a hole through the wood after the beam has been amplified by the lens.
- This one pulse at quite a long distance from the work was so explosive that debris became deposited on the lens. Always reinforces the need for air assist protection of the lens
- The same pulse test but through 10mm plywood this time. .Burns a parallel hole right through
- Importance of air assist and how the air assist need not be high pressure, just efficient at getting air into the kerf.
- How is it possible for a diverging beam below the focus point to burn a parallel hole through 10mm? a BIG unanswered question
- Small distance to work and small nozzle orifice jets the air assist efficiently into the cut and leaves almost char-free edges
- We establish that a flow though the nozzle at 8l/min will be the air assist air flow for all our tests because we have proved that air assist flow rate can affect cut efficiency.
- After many hours of off camera work the results are here to be viewed. Comparing just how fast we could run each of our 38mm lens. It was surprising to find the cheapest Chinese PVD plano convex scored best.
- As an extra unscheduled test, I used a 50.8mm GaAs and ZnSe PVD lens to compare cutting performance against their 38.1mm brothers..
- Wow, they were several steps more efficient. But why?
- Logic says that if I put say 60watts into a 38mm spot size I get a certain energy density to damage the material I am cutting. Move up to the next focal distance 50.8 and the spot size is twice the area. Thus, the energy density is halved, and we should therefore do LESS damage to the material. Results do not support that logic . The 2” lens cuts better but why?
- Still more understanding required… but that’s another day after a lot more research.
- How to use a laser cutter videos
152 Are Our Nozzles Designed Correctly?
- Did the Chinese put any real thought into the design of nozzles?
- Test 1 is to see just what size the beam is that arrives at the lens. The answer is the same size as the tube window i.e., 12.7mm
- EFR claim this to be a 6mm beam.
- Equipment setup to establish the profile of the beam as it exits the lens
- Microscope look at the burn results
- Cad drawing to put those results into perspective for a 38mm lens
- Discussion of results.
- There is no information anywhere to say what lenses and what nozzles are supposed to work together.
- Discussion about the defined spot size of the tube beam
- Run similar tests for 2 “ and 2.5” lenses with different nozzles
- Discussion about what size orifice would be beneficial.
- Did the designer specifically use the nozzle as a low power occlusion device?
- OR did they work from the tube manufacturers beam diameter data?
- I need to do some more research before jumping to any serious conclusions about what we have discovered in this session.
- How to use a laser cutter videos
153 Nozzle Analysis Part 2
- Discussion as to why there is such a difference between beam diameter that I can prove exists and the tube makers specification.
- Is it all to do with FWHM?
- I think it’s more likely to be a NORMAL distribution definition because our beam has a power distribution that is Gaussian (otherwise known a NORMAL)
- When we realize that 2 standard deviations is about 8mm and that 95% of the beam power is within that zone of the 12.7mm beam it begins to make sense that we should not worry about obscuration at the extremes
- All nozzle/beam combinations now will work without any noticeable power loss or nozzle heating.
- The difference between the needs of cutting and engraving really demand different nozzles
- Power tests before and after nozzle to see if there are any significant power losses caused by the nozzle.
- The conclusion is less than 2% so not worth worrying about and no reason to change the size of a CUTTING nozzle orifice.
- Demonstration of the many problems and principles of engraving when using a CUTTING nozzle
- I have developed a dedicated engraving nozzle specifically for engraving
- The explosive volcanic debris no longer gets near the nozzle because the rapid CROSSFLOW of air is pulling it away before it can reach the nozzle
- This nozzle (and many other goodies) can be bought at Cloudray Make sure you scroll down the page for lots of useful data
- How to use a laser cutter videos
154 Head Transplant Mk2A
- Here we are at the final iteration of the new head design
- Cutting the parts for the new design with the old design head.
- Stepping through the assembly and cementing the parts
- I must stress that this design is suitable for the China Blue machine with its front mounted bearing rail
- Your table must be adjustable to use this system
- New switches fitted to allow small adjustments for focusing.
- Fit the new head and look at new target holder.
- Set initial head position to “catch the beam from mirror 2.
- Go through the Z setting procedure we are now very familiar with .
- With the machine set up we quickly go through the many NEW combination of lenses and nozzles
- How to contact me about the drawings and the mounting bracket. The latter can be bought, or you can make it yourself.
- Discussion of the opposite requirements of cutting and engraving
- Look at all the all the possible combinations of lenses and nozzle and the fact that you can use a clamp ring as a backstop instead so that you project your focus point to a position that suits you beyond the nozzle.
- My rant about honeycomb tables. It’s the thing all makers supply but the WORST possible thing for air flow management , cannot be cleaned, damages the underside of your work and after a few months of use become a fire hazard
- How to use a laser cutter videos
155 Oh Dear, What Nozzle and Lens do I choose?
- The work I have done recently with the new head has forced me to look much harder at the fixed design of lens tubes and nozzles that has not changed since forever!!!
- Life was simple when the choice was just one of 3 main lenses j and just one nozzle
- With all the 3 possible nozzles, many lenses, and different ideas for mounting them in ways you had never imagined……..the matrix has exploded.
- Here step through all the new combinations
- At the time of the video the universal engraving nozzle was not existing. But now you can go to Cloudray.
- Make sure you scroll down the web pages because they are full of useful data
- How to use a laser cutter videos
156 The Holy Grail of Dots
- I already have discovered the secret formula for a compound lens.
- People have questioned whether I had tried all possible combinations. The answer is no and there are too many combinations to try in what precious time I have left to breath……But I am going to explore lots more just in case there is a pattern that will point me to something better..
- A demonstration of the methods I will be using to try and find the magic combination.
- With so many lenses in my collection and they all look very same-ish, I am often asked how can you easily determine the local length of a lens? Answer is that I have made myself a “lens ladder”
- Most people cannot easily work out what a meniscus lens looks like. Here is a simple fool proof way of sorting meniscus from plano convex.
- We will run all test at a standard power and speed.
- Let’s look at the microscope picture of our combinations. Most are rubbish but a few standouts.
- Why do I get halo-free dots? Is it because of my power filtering theory where exaggerating the spherical aberration sends the high-density part of the beam to a significantly different focal point or is it because there is a concentration of everything through a perfect focus point?
- When we look at the 4 best halo-free results from 19 combinations there is one obvious pattern, those 4 are all flat side down combinations.
- Back to the workshop to retest the two best combinations for repeatability
- Choice 1 is not repeatable but with some fiddling it come back to almost good.
- Test for the #1 choice to see if there is any lower power around the dot. Hmm. Good but not perfect
- Now do the same test with our original best combination
- Wow. No dot growth or low power halo after continuous burns of several seconds. Absolute perfection. ALL the power must be passing through that single point. Zero aberration effect.
- We have come full circle and learnt nothing other than how perfect the original combination was.
- We now test this combination with and image on some VERY thin card. This is a challenging test and to show that we are not burning though and that we have delicate control of the power per dot.
- We test also on anodized aluminium. We find that we can get smaller dots, so we set resolution to 318ppi and get a great result
- We repeat the picture test with MF and again get a great result.
- You can now buy this compound lens kit at Cloudray.
- Make sure you scroll down the page foe some great details.
- How to use a laser cutter videos
157 A short Break
- I am trying some laser rehab, but I’m not sure it’s working!!!
158 Compound Lens and Universal Engraving Nozzle
- The universal engraving nozzle /compound lens kit has arrived from Cloudray’ It is officially now a purchasable item
- Cloudray No4 Compound universal engraving Nozzle make sure you scroll down the webpage for lots of good data
- This is just a painbrush…….it will not make you a brilliant artist. There are many basic rules I have laid out for you. This is not intended as a cutting system it is designed for low power dithered engraving and may be of no use to those with powerful 100 watt plus tubes if you cannot control low power in a precision manner.
- Choose the card, wood, slate, etc carefully because not all materials react the same to IR light.
- Dot colour is the key thing to look for when you do your dot test.
- Here is what you get in a compound lens kit.
- And how to assemble it.
- The worktable must be true to within better than 0.3mm
- Set the focus spot on with the dot test pattern so that you get sharp black dots
- You must have a picture with a natural resolution greater than the image you are going to engrave. You can always down scale the resolution without detail loss but if you upscale you are degrading the picture.
- Always scale your picture in RDWorks before you set the output resolution.
- In the bitmap handle set the output resolution to match the size of your dots and the dither with dot mode.
- Set the parameters for engraving especially the line interval.
- For card engraving I have made myself a little vacuum table (a future video project) that hold the card perfectly flat.
- It is important that we engrave from the bottom of the image towards the back of the table
- Demonstration CROSSFLOW air through the machine and how important it is for nice clean engraving.
- Fantastic image at 245 dpi why would you want more?
- Now for Baltic birch plywood, a nice white fairly grain less material. The only issue with it is flatness. The Mk1 vacuum table is not powerful enough to suck it flat
- Now we see the advantage of a flat steel table as I use neodymium magnets
- Trying different parameters for the dot test seems to limit me to a 0.15 dot i.e., 170dpi
- The results were OK but obviously dotty
- Rerun at 254 dpi the result was just amazing
- So wood was not the problem I had anticipated, but this was an almost grain less wood. Anything like bamboo or other grained woods may produce some very strange results because the grain resin engraves differently to the surrounding cellulose.
- Summary of what you will get when you order parts from Cloudray
- How to use a laser cutter videos
159 The Chequerboard Challenge
- A light bulb moment a couple of months ago was going to allow me to produce high quality dithered images at high speed ……or so I thought. Quick and dirty testing at the time were a total flop.
- So, in this session, after lots of thinking during my laser rehab, I am going to give the idea another try. It may turn out to be a genius idea or a public demonstration of my senility
- A look at the 254-dpi chequerboard pattern i.e., pixels and spaces are 0.1mm
- We set the parameters and specifically set the scan mode to X unilateralism
- I interrupt the test to CUT a special high resolution focus gauge specifically for setting this compound nozzle This will answer questions about can this compound lens cut?
- We established focus and power using the dot test and then run the chequer pattern at the best focus distance
- Pretty good results, Nice clear 0.1mm dots on my test card
- Run on anodized aluminium and Laser Tile the results are equally good.
- On wood the dots pattern is still there but the resin in the grain is “banding” the pattern
- Final test on the beer mat card shows the 0.1mm dots or better pattern also
- Calculating the response speed of my power supply since it can burn single dots cleanly at 200mm/s, tells me it is 0.5ms response time or better, which is twice as fast as the promised specification..
- Can we run at 400mm/s? Amazingly YES!!!!
- But I will still proceed to test my original genius idea
- Explanation of why an RF tube can run so much faster engraving than we can with our DC controlled tubes.
- A diagram of how the tube is being switched on and off to produce the chequerboard pattern. The power is pre-set to a fixed value to create the right amount of burn and then the tube switches on and off to burn the dots. Key thing here is the tube is SWITCHING on and off.
- We are now going to walk through what greyscale engraving is that we normally use for 3D engraving.
- So how will the tube now be controlled when the OUTPUT DIRECT switch is enabled
- The tube now switches on for a whole scan line and then switches off. During that scan the power is the feature that varies, and it can vary from one power level to another at almost instant speed.
- The problem is that if ever the controller detects true white (255) then it will switch the tube OFF and now the tube must restart at a relatively slow speed before it can carry in with its rapid power variation.
- We must therefore modify the greyscale picture to remove any pure white pixels. This will be done in Photoshop or some other image manipulation program like GIMP.
- BUT, before we do this we must convert the picture into a binary dithered image containing black pixels on a white background We must now convert this binary bitmap back to a greyscale image and use the LEVELS feature to reset the white 255 to say very nearly white 250. Doing this will fool the controller to never switching off because it will never see 255 white pixels.
- Now the problem is to find the correct max and min power settings to print the dot and running at a speed of 600mm/s
- The final result was pretty good but nowhere near as good as a normal dot dithered picture.
- The genius idea was not an abject failure but for our machines it seems that slow speed high quality it will have to be rather than high speed with a just about OK quality
- How to use a laser cutter videos
160 Adobe CS2 Legally Free (RE-EDITED)
- Although lots of websites point you to the Adobe.com download page and advise that this version is now freeware, they are misleading, as I found out to my embarrassment.
- I have had to re-edit this video assuming that you are in possession of a copy of Photoshop, even old version will have the basic features I will be using. You could also use GIMP which is an open-source FREE variant of Photoshop
- I am NOT any sort of Photoshop expert I am just an ankle-deep paddler; however, I know just enough to understand about creating the correct resolution pictures to work with our laser machine.
- The first thing to understand is the resolution of the original picture. When you look at its properties it will almost certainly display at a resolution of 72ppi. This is the standard www format for transmitting and displaying images.
- Panic not, because if you look at the top of the properties box and see that your image is several megabytes, then all the original detail is still there somewhere.
- If you untick resample image and set the resolution to the best we can engrave (254ppi), you will see the picture has resized. Now provided the size is bigger than what you want to engrave then you can proceed.
- We leave the original image unchanged and create a NEW window. You can now specify exactly the size and resolution of that window that you require for your final image
- You can now drag your original image into the new window and start to shrink and position it to suit.
- You can now convert to greyscale and play with your image using a myriad of controls to adjust contrast brightness etc . One useful tip is to see what filter unsharp mask does to make your picture “pop”. Use sparingly.
- Finally, you can convert to a bitmap and chose a simple diffusion dither
- Save as a.bmp and import into RDWorks
- Set the parameters
- Before you start engraving you MUST make sure you have set your Scanning Offset correction for the speed you plan to run your engraving at
- Need to satisfy myself that everything engraves ok so a quick test on beer mat card and then on Baltic birch plywood.
- I take the opportunity to experiment again with my genius idea to greyscale engrave a dithered picture
- Results are as before, about 90% quality when compared to ordinary dithered engraving.
- How to use a laser cutter videos
161 Christmas Special 2018
- Let’s get the party started!!!!
- Making my mince pie a little bit more festive
- Making labels for your seasonal gifts
- Getting your Christmas cards ready for Xmas
- Embossing the card with snowflake pattern
- Now for the inner paper part of the card
- Inkjet print the inner sheets with a seasonal message and assemble the final card.
- Special jig for A4 Baltic birch ply. Holds it flat and the jig is fixed at a known position so that I can program items in Absolute Mode
- First the card packing wrap for the coasters
- 3mm Baltic birch ply coasters.
- Transfer coasters to the engraving jig
- Creating an image for engraving using the VIRTUAL array method
- A pretty good Xmas gift?????
- A surprise present for my lovely wife!
- Not something I made at a mad price
- Christmas greetings.
- How to use a laser cutter videos
162 Lens tests Part 1
- The “ironman” tests we did on lenses a few sessions ago was very thought provoking because some of the results and effects that we take for granted defy logical reasoning
- We think of focus as a fixed entity, but practical experience tells me it’s not. It can vary with speed and power
- First question is where is the manufacturers focal point?
- Diagram and measurements to find where the focal point is.
- Clear demonstration that the focal point is not where the manufacturer set it and it changes with speed!!!
- Crude test to demonstrate the beam fanning out before and after the focal point.
- A look at the results under microscope shows a curiously uniform diameter hole where the material damage threshold has been exceeded. That hole is not fanning in and out with the beam spread. Curious??
- Carrying out more tests with constant pulse power per burn.
- Looking at microscope images and pointing out that I cannot produce a static dot at 2ms whereas dynamically I can lay dots that happen in 0.5ms Curious???2
- Difference in damage threshold for two different card types
- Microscope view of different focal length burn profiles
- Trying to find the best way to display the results
- Scale drawings of the various focal lengths show some surprising results.
- Let’s try something ridiculous with a 2.5” GaAs lens. A block of 10mm thick acrylic set 9mm below the focal point using all the previous test parameters.
- Acrylic damage threshold is significantly different, but we can still make a small hole in the surface so even at this extreme distance there is still some high central energy density
- By increasing the TIME only, we allow the available energy to act on the acrylic. 1 second allows this DEFOCUSED beam to burn a virtually PARALLEL hole through10mm material. Even more curious??
- One more test to see the shape of a 1 sec burn done with the material set at the focal point and then 9mm above the focal point.
- The results are still almost parallel holes regardless of whether the beam is converging or diverging
- Questions about this phenomenon have been asked of MANY experts and learned establishments. No satisfactory explanations have been forthcoming.
- The theory that this effect is due to the light pipe effect of total internal energy reflection is logically dissembled.
- Conclusion is that there seems to be a thin core of high energy that is doing this damage.
- How to use a laser cutter videos
163 Lens Tests Part 2
- It seems that lens theory is not quite the same as lens practice. There are some interesting discoveries that do not appear in books. The beam’s energy density does not just happen at the focal point
- We have a demonstration of the method used to map the energy density within the beam both above and below the focal point.
- Each lens being tested is set to its perfect “dynamic” focal point and the table is dropped 20mm below that focal point , The pulse power is set to 60 watts for a fixed 20ms pulse
- A “burn” is made in a piece of thin standard test card.
- The table is ten raised in predefined steps all the way to 20mm above the focal point and “burns” are made at each step.
- We see the holes caused by the high energy part of the beam and the halo around the hole where the out of focus lower energy has only been able to scorch the card.
- The test is quite quick but measuring the result and converting it into a meaningful graphical format is a laborious process.
- It’s necessary to collect this data before trying to work out why different lenses cut the same material at different speeds and different cut profiles AND why the same lens cuts different materials at different speeds.
- A detailed look at the many different lens materials, lens shapes, orientations and powers used for the tests
- A detailed explanation of different lens types and the way they focus the energy
- Our Chinese lenses are not capable of achieving anywhere near the published “spot” size
- That is clearly demonstrated when a comparison of the same lens tested 4 different ways is neither consistent nor anywhere close to the generally accepted spot size.
- Testing a special 4” lens configuration to find a “super” small spot size
- Disappointed at the cutting performance I created a density map to see what was happening. Basically, it was rubbish. But upon reading the small print, the super small spot was claimed for a completely different wavelength light.
- An explanation of how I arrived at selecting a 20ms pulse length and comparing it with a 50ms pulse length
- How to use a laser cutter videos
164 Honeycomb Alert
- As You will quickly discover, I hate the honeycomb table.
- A quick discussion about airflow management THROUGH the machine
- Understanding CROSSFLOW and how honeycomb circumvents it
- A demonstration of how there is almost zero extraction from under your cuts and the refection marls on the back/edge of your cuts.
- The cold condensing honeycomb is a fume trap.
- Watch the condensate build up beneath the work, the back reflection flashes, and the occasional orange glow in the background as the fumes catch fire in the cells.
- Replacing the honeycomb with a mild steel sheet forces the air flow ACROSS the table and out the rear grill
- Demonstration of acrylic cutting directly on the steel table to show the fumes condensing on the cold surface (no back marking or combustion.)
- A demonstration of how easy it is to ignite acrylic once it is warm.
- View of damage done to the steel table by the excess energy (once the cut is complete). It is this excess that will ignite the condensate build up in the honeycomb cells
- Introduction to the NEW machine that I have been gifted.
- Yes …this was an acrylic fire!!!!!
- Honeycomb and acrylic have been responsible for at least 5 other machine fires that I have been notified of .
- NEVER walk away from a machine whilst it is CUTTING and keep a small fire extinguisher by your machine.
- How to use a laser cutter videos
165 Making a Vacuum Table
- Apologies for long wait for this video
- Quickly skip over the cutting of pieces and on to assembly
- Removing the fans from the Mk1 vac table ready for reuse
- Loose nuts mean I must use nylock nuts for the MK2
- Assembly procedure and instructions for gluing.
- Wiring the fans into the MK2
- Explanation of why two fans are stacked
- Make sure the power supply has enough current draw for all the fans
- A quick test shows all is working great.
- There is a modification in this Mk2 with a FRAME of screws to pull the edges of Baltic birch plywood flat for engraving
- There is a 3-point levelling system that will allow you to achieve levels better than 0.1mm
- Details of the design are available on the RDWorks lab forum
166 Lenses Part 3. Cutting Test Preview.
- Worried folks are reassured about my non-existent health problem because it was a couple of weeks since my last video…. They were either genuinely concerned or sarcastically telling.me to get my finger out. I advised them that this was not a soap opera, and it would continue at MY pace and that the only thing I must suffer is my wife!!!
- Introduction to the MASSIVE task of testing the many lenses I have now got in my collection.
- Setting the focus on the test lens. Test with the 200mm/s speed (too fast) and then slow down to cutting speed (25mm/s). Focus changes by about 1mm when running at the correct CUTTING speed
- A look at what happens beneath the material at different cutting speeds and the efficient way in which my managed air flow removes the fumes.
- Analysis of the BACK of the cuts to choose the fastest reliable sample.
- I have purpose put a small crosscut into the sample so that I can examine the profile of the beam path,
- To do that I grind about 2mm away so that I can examine a “clean” profile.
- Now a simple test on a piece of card to check the size of the beam on entry to cutting the 10mm thick poplar plywood sample. Then a second burn on the card with the table lowered by 10mm. This demonstrates the shape of the beam at exit of the plywood,
- When measured, the card shows an entry burn of about 1mm and an exit burn of about 5,5mm.
- So how will this same 1,5” lens perform on 10mm acrylic?
- The 4mm/s sample was selected and the crosscut profile ground away’
- We now look at the entry profile of the plywood sample and it measures 0.5mm wide.
- A measurement of the cut exit is 0,4mm wide
- The whole cut profile shows a slight barrelling.
- Now a look at the acrylic cut profile shows it to be almost parallel and 0.4mm wide,
- Examining the results in picture form clearly shows the puzzling aspect of cutting and lenses
- Conventional wisdom would suggest that an increasing beam profile below the focal point will result in a tapered cut i.e., the cut edge will never be square,
- Trotec peddle this myth as though it was scientific fact and that THEY know the way to overcome it is with a longer focal length lens. Hmm
- Does this mean we can do much better cuts with our cheap Chinese lenses?
- How to use a laser cutter videos
167 Auto Focus Frustration
- A little Russ rant about the uselessness of the autofocus system.
- BUT…now I have changed my lens test procedure to include another feature that is the subject of MUCH debate. Will I get faster/deeper cuts if I drop the focus into the material?
- I can now use the autofocus to automate this test procedure.
- Hmmm. Problems, problems, and more problems.
- A quick run through setting the autofocus pen (switch) and set the switch to leave the nozzle on the work surface
- Upon initiating the autofocus cycle the table drops by about 3mm below the nozzle. Why?
- A look into the vendor settings to see a feature called HOME OFFSET on the Z axis is set to 3mm. Change this to zero and then do a machine reset
- You would expect the nozzle to now sit on the work surface….NO!!! Why not?
- The switch has 3 positions. If you set the sensor(switch) up incorrectly you will damage the switch
- So how do I set the nozzle to my required 7.5mm perfect focus distance?
- Back to the vendor settings and in the Z HOME OFFSET and set the 7.5-1.5=6mm
- Run the autofocus again and now the focus is perfect.
- Under non-demonstration mode that would take about 5 minutes to reset the switch for a new/different lens.
- Now we start to program for the simple task of raising the table 3mm between layers,
- There now follows a long and confusing set of steps as I try to decode the Chinglish instructions for making the table move between layers,
- Eventually it becomes clear and simple, and we see a demonstration of the function in action.
- How to use a laser cutter videos
168 Bridges
- A solid table means raising your work to get good airflow beneath the material. In doing so there are two possible problems you create
- Any pieces that fall down start blocking the airflow and secondly those pieces may fall out of line with the cut profile and land in a position to be damaged by an adjacent cut.
- Bridges solve this issue.
- Bridges allow you to raise your work well above the zone where reflection from the metal table damages the rear of your work.
- Although I have engraved simple outline letters on the acrylic job, I have left the protective film on. This acts as a mask when I want to paint fill the letters.
- We take a quick look into RDWorks to see where and how you can add bridges to your objects.
- Removing the film and tidying up the filled letters.
- Finally, a bit of housekeeping. Cleaning the condensed acrylic vapour from the table with acetone.
- How to use a laser cutter videos
169 Auto Focus Practical Alternative
- Confirmation that I am not a fan of the auto focus systems on these machines.
- I plan to show how you can use your Z stepper system to get auto focus capability without using the vulnerable auto focus switch.
- In the USER tab set the AUTO HOME for Z ON.
- This only works if you have a top sensing micro switch.
- When you press RESET the Z table now resets to its TOP position and sets the keyboard display to ZERO.
- There is a risk of wiping out if you leave something on the table. You can overcome this you must set your RETURN POSITION to absolute.
- Demonstration of the machine being confused about the work ORIGIN point depending on running from machine memory or live from the PC.
- Choosing to use Absolute or Anchor Point positioning in RDWorks solves this confusion.
- Demonstration of variation in focal distance as the lens orientation changes.
- To find the best focus set the speed for the application you plan to run and with a straight line find the thinnest drawn line.
- Check the settings in Vendor Settings (RD8888) and set the HOME OFFSET to 0
- Changing the speed appears to change the focus…. Hmmm
- Setting and using a program with varying Z positions.
- Never assume that the machine vendor has calibrated the Z-axis. Check it for yourself and set the calibration as described.
- How to use a laser cutter videos
170 Let’s Focus on Lenses Part 4 (First results)
- Despite. lots of hunting, I came across zero research work on how lenses cut no-metallic material. That means I must find the answers myself.
- Thanks to Cloudray for supplying many different lens materials, focal lengths and lens shapes that have enabled this comparative work to take place.
- Stepping through the methodology I use for my tests
- The key setting is focus for each lens. As we have seen before, the focus must be set for the speed of testing.
- Demonstration of my program to quickly find the correct focus.
- Running one of my standard tests.
- Analysis of the test results.
- After many hours of testing, and result logging I have collected all my results into a PDF file.
- My goal is to find out exactly what happens to a material when the laser beam strikes it . I already know that standard lens theory is meaningless in answering this question.
- Quick discussion of the 3 materials I chose to test, Plywood, acrylic and MDF.
- There are many myths and “old wives’ tales” that need to be examined
- A look at the summary page of the cutting results for all lenses and materials.
- Using the test data summary to confirm or debunk the myths.
- My favourite cutting lens is a 2″ focal length gallium arsenide used flat face down. Using Practical results, I show just how wrong I have been!!!!
- The big question that is evident in all the pictures remains…. WHY if a lens causes the beam to DEFOCUS after the focal point, do we get DEEP and PARALLEL cuts?????
- How to use a laser cutter videos
171 Lenses Part 5. Why are cuts Parallel?
- After much time and effort carrying out energy density profiling all the test lenses, I’m not sure that they help answer the “why parallel cuts ” question.
- We can clearly see from tests that we get parallel sided cuts in 10mm thick MDF with both 1.5″ and 4″ focal length lenses regardless of lens shape or lens orientation, that is contrary to all we have been taught about lenses.
- Oh, dear some of my infantile attempts at drawing!! I try to explain my theory of how it is possible to get a parallel cut.
- I use some 10mm thick extruded acrylic to try and examine my theory.
- Using a fixed power but pulse lengths from 1 to 10ms we can begin to see the “mode burn” of a focused beam as it penetrates the acrylic.
- Carrying on beyond 10ms produces interesting results.
- The proposal that vapour is being reheated and scourging the side walls as it exits is tested with a sandwich of thin acrylic sheets and air gaps to vent any trapped vapour.
- During a short holiday in Greece , I had lots of time to think about this problem. The sun, salty air, wine and too much food seemed to supercharge my two remaining grey cells into connecting all the data dots I had created into a crystal-clear image of what was happening.
- How to use a laser cutter videos
172 At LAST!!! How Lenses Work.
- I cannot begin to bullet point this session because it contains so much data. You are going to have to watch it (if you can stay awake).
173 Dead RDC6442 control panel
- After 4 years the display screen has stopped working
- Remove some clamps to remove the panel
- Various suggested fixes from the internet all fail.
- Had to buy a new display box and yes that fixed the problem and I now have my machine back
- During the intervening 2 weeks I was without a display panel I was forced to control the machine from my PC…. a new experience for me.
- The TEST tab is limited and different way to manually move the head around the work area.
- We have a quick demonstration of these features
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174 Should I use an inert assist gas?
- This is a VERY short session!
- I have often been asked if an inert assist gas will cure the charred edges that happen when we cut an organic material such as wood, leather, or card.
- The atmosphere we breath is 80% inert anyway (nitrogen) but about 20% is highly reactive oxygen which is required for the chemical action of burning (oxidation)
- I have borrowed a bottle of argon gas (very inert) from a welder friend.
- I carry out a test cut with normal air assist on a piece of 10mm poplar plywood. The result is a light brown, but char free cut at 8mm/s with my 60-watt tube.
- I now change to argon assist gas and repeat the test exactly. having set the argon pressure to about 4psi to match the normal air assist pressure
- Two surprises arise from this test.
- A) there appears to be no reduced cutting efficiency because we have hopefully excluded oxygen
- B) There is ZERO difference in the cut edge colour.
- Thus, I ask why would I use an expensive assist gas when normal FREE air will achieve the same result?
- Hopefully this ends the speculation about the benefits of using and inert assist gas.
- How to use a laser cutter videos
175 C Series Head adjustable bracket
- This session begins with an unfocused beam MODE BURN. The purpose is to show an imperfection with my beam. The central “sharp” light intensity is missing.
- This makes it difficult for me to get crisp dots and detail in my photo engraving. A change of tube is required.
- Changing the tube is not a difficult task but setting the beam perfectly is difficult with the existing head because it has no Z axis adjustment.
- I now rip the head off the machine.
- Introduction to my stainless steel fully adjustable head mounting bracket
- The new bracket has been designed to completely copy the previous non-adjustable bracket
- Rebuild the head bracket so that you can see the assembly procedure
- You will see how the head is now easily adjustable in Z and Y
- We have not messed with the X or Y-axis so it should just be a simple matter to move the head so that the beam lands on the mirror 3 sweet spot.
- On turning the machine on the Z axis jams as it tries to home. The culprit is soon identified as a small piece of acrylic waste that found its way into a lead screw thread.
- We now step through the procedure for setting Z perfectly.
- Adjust the head in Z and Y to get the beam approximately on target centre
- With the power set to 15% (approx. what is used for photo engraving) it is obvious that the power at the centre of the beam is missing.
- This centring procedure does not have to be spot on because it is going to be readjusted at a later stage.
- The next procedure shows how to set the Z axis perpendicular to the table.
- The next procedure uses a special fixture to hold a target on the AXIS of the lens tube. A critical setting will now take place and that is to adjust the head position in Z and Y so that the beam reflects off mirror three right onto the centre of the target.
- When you have achieved this, you can be sure that the beam is passing through the AXIS of the lens
- So that’s the beam reset
- We now look at a different pin table support system. A series of fully independent pins.
- we now make new targets for the Z alignment fixture that will be required when we replace the tube.
- This adjustable bracket is not something I wish to manufacture so I am giving the design to Cloudray to manufacture and sell at Chinese prices.
- See Cloudray C Series CO2 Adjustable Laser Head Bracket
- This is designed to suit the 15mm bearing rail system. Be warned, many machines have a 12mm rail system and at this stage cannot be used with such machines.
- How to use a laser cutter videos
176 A New Tube for the Lightblade.
- I cannot no longer do the same quality of photo engraving on this machine that I can do on my old China Blue machine.
- We do mode burns on both machines to demonstrate the problem I have.
- I demonstrate that as a CUTTING tube it performs well but for engraving it lacks detail.
- For most people it seems insane to change what looks like a perfectly good tube. My needs and standards are well honed and tell me that this tube needs replacing.
- We look at the new Cloudray CR70 tube and discuss it SPT pedigree.
- We check that the tube will fit existing clamps and that the 60-watt power supply will work with a 70-watt tube. Ideally, I should buy an 80-watt power supply.
- We rip out the old tube and install the new tube, showing you how to make the soldered high voltage cable joint.
- We look at how to clean molybdenum mirrors in extreme ways.
- Using my card targets we set the beam spot onto the centre of mirror 1
- We then go through the procedure for setting mirrors 1 and 2 to set the beam true to the Y and X axes.
- The more observant will note that my prototype bracket design, clashed with the belt path. Panic not. it has been fixed.
- We now step through the same Z setting procedure that we covered in video #175
- In addition, we also check beam alignment through the nozzle and make minor adjustments to mirror 3
- We check the performance characteristic of the new tube against the tube we removed. It delivers MUCH more than promised. This is a 70-watt tube delivering 85 watts!! That is typical for SPT. They are the only company I know of that UNDERSPECIFY their tubes.
- We then compare mode burns and see an amazing improvement
- We then do a known photo engraving test to verify that we have detail back in the results.
- How to use a laser cutter videos
177 Christmas Special 2019.
- After celebrating with stollen and red wine, should I be using this very dangerous laser machine????
- First, we are going to make some Xmas decorations called Plop Plops.
- Next, we start on another project for that time after dinner on Xmas day.
- We are using bridges that we learnt about in an earlier session
- We make more interesting pieces but still no clue about the final item!!
- Finally, we can see that it’s a 4x4x4 3D tic tac toe.
- We then make a nice box to pack it away.
- Finally, we overcook the turkey!!
- How to use a laser cutter videos
178 Another New Venture
- I have been loaned a fiber laser machine for about a year to “play with”
- Lotus Laser sounds Chinese but, they are very British and are only a few miles away from where I live.
- These are not Chinese imports, but UK designed and manufactured bespoke machines.
- This machine is a rare and expensive breed of equipment called a MOPA fiber laser.
- I know NOTHING about the technology so why do I have the luxury of borrowing this machine
- Starting from nothing means I may learn many things about this machine that Lotus Laser do not have time to discover for themselves
- I will not let this new venture interfere with my RDWorks series so I will call it a new name so those with no interest can pass it by.
- How to use a laser cutter videos
179 Fitting the Cloudray C Series Adjustable head
- I have received the prototype head bracket from Cloudray for approval before they go into production with it
- To make sure that it all works perfectly I rip off MY original prototype and refit the new design.
- All worked perfectly
- We then went through the Z setting procedure we have seen in previous sessions
- So now the product is available for sale at Cloudray C Series CO2 Adjustable Laser Head Bracket.
180 Axis switch not working
- The Hall Effect proximity switches that are used to set the 0,0 position when you first turn on the machine can cause some puzzling machine effects when they fail.
- We step through the controller start procedure to see how these sensors are used to set the machine’s work area.
- How to check if your sensors are working.
- Description of how the switch procedure operates
- Demonstration of how the switch is used to set the axis zero point.
- So, what goes wrong with these switches?
- It will almost certainly be an X axis switch that fails because the copper wires are not good at flexing and this cable flexes continuously.
- We talk about how where and why the cable will flex to destruction and how intermittent connections of the break can fool a lot of people to look elsewhere for a problem.
- Description of where and what to buy to replace the switch
- A little trick that allows you to use your machine whilst awaiting a replacement switch
- How to use a laser cutter videos
181 Redsail Clone Upgraded Head
- My Lightblade machine is a Redsail clone. This is not a derogatory term but a description of a basic machine design where gantry is kept square to the Y rails by two synchronized toothed drive belts
- The Lightblade is built like a tank and has 15mm linear bearing rails. Most red and black machines have 12mm rails
- The mounting bracket I designed for this machine is now available from Cloudray
- However, it is designed for the 15mm bearing system, but I have designed an adaptor plate which allows this head bracket to be used with 12 mm bearings.
- Cloudray is changing the design of their C series lens tubes to presumably make them cheaper. They will be plain 24mm diameter in future.
- This prompted me to consider a completely different strategy for the head design based around using the amazing lens and nozzle flexibility of the C series lens tube.
- Instead of the existing very heavy head I have designed a minimalist piece of aluminium origami that weighs less than half of nothing!!!
- It employs many novel design features to improve stability and lens tube location accuracy. A very simple “butterfly ” clamp locks the tube solidly into a vee block location. This allows quick and easy adjustment and removal of the lens tube.
- I now demonstrate how the head is manufactured in a few simple stages.
- The whole point of making a lightweight head is to improve the speed performance of the machine.
- Shorter cycle times (mainly for engraving) are slightly dependant of linear speed but much more influenced by acceleration. We only have a certain fixed power available from the stepper motor so the lover the moving mass the greater we can accelerate it with the available power.
- There is a brief explanation of how Newton’s second law of motion is relevant to this acceleration problem.
- There now follows a series of tests with the existing head and machine settings to demonstrate the increasing overrun as speed increases
- 350 grams is the weight of the original head and 101 grams for the new design.
- The new head requires the bracket to be modified and the lit contains a drill jig to add hole to existing brackets. NOTE New brackets from Cloudray now have these holes
- I show the new head being fitted to the machine and the detailed setting procedure for the Z axis
- At 500mm/s the overrun was 22mm. Without changing any parameters, the overrun with the lightweight head becomes 17mm
- The acceleration limit specified in the Vendor Setting is 10,000mm/s/s .I cautiously raise this to 15,000mm/s/s and them go to the USER settings and find the acceleration is set to 8,000mm/s/s.. I set it to 15,000mm/s/s.
- Testing at 500mm/s shows the overrun has now decreased to 13mm
- I raise the vendor setting again and set the acceleration to 20,000mm/s/s. This results in an 11mm overrun.
- I now examine what happens when I raise the speed to 1000mm/s. I find we are running twice as fast, but the overrun is now at 30mm
- Without hunting for optimum parameters, we test at 400mm/s and get about 6mm overrun. indicating the running slower with high acceleration factor creates a shorter cycle time.
- Will this high speed /acceleration result in ringing of the new head bracket in the Y direction? No. My little dot test program proves all is stable and stiff.
- Review of Newton’s law showed that we could force the acceleration from 20,000mm/s/s to 30,000mm/s/s and not be loading the motor more than the original head.
- That 30mm overrun at 1000mm/s has now reduced to 23mm but the cycle time is 14 seconds
- Drop the speed to 500mm/s and the cycle time becomes 14 seconds —no different
- Run at 600mm/s and the cycle time becomes 13 seconds and at 700mm/s the result is 12 seconds
- So somewhere between 500 and 1000mm/s there is an optimum speed that produces the fastest overall cycle time.
- We then review something obvious. That same 12 second portrait pattern is rotated to landscape resulting in a cycle time of 10 seconds!!!!
- How to use a laser cutter videos
182 Oh No! Not another new head
- Having designed and fitted a lightweight head to the Lightblade machine it seemed a “no brainer” to find a way to make it fit the China blue machine also
- We look at the problems. Big Y axis alignment issue and, despite the rigid mounting opportunity straight onto the X axis bearing, there will only be Z adjustment on the head.
- This forces me to review the design of the #2 mirror mount and design something different that has precision Y adjustment to compensate for loss of Y adjustment on the head itself,
- I manufacture and fit an acrylic no2 mirror mount
- I eventually get the new head fitted and the beam aligned in the Z axis ready to use.
- With existing parameters at 500mm/s and an acceleration of 3,000mm/s/s there is huge over travel of 37mm
- Changing the acceleration to 30,000mm/s/s reduces the overrun to 5mm!!
- Run a test pattern to check for loss of steps….none.
- How to use a laser cutter videos
183 New head results.
- Having previously run photo engraving at 200mm/s. I am now able to run at 400mm/s with no loss of quality.. The overrun is only 2 or 3mm and the cycle time has reduced to less than 50% .
- This is a tube that is now nearly 5 years old, and this is just a quick footnote to verify a 120% successful head transplant
- We look at all the parts of the kit that will be supplied and sum up how they fit.
184 Lightweight head news
- Just a quick session to inform that Cloudray will not be making this new lightweight head people because with no news back from China, the demand for it is increasing. I am therefore forced to make and sell a small batch myself. (Not a responsibility I wished to take on……..BUT)
- We look at all the parts of the kit that will be supplied and sum up how they fit.
185 Lightweight head update
- My small batch of lightweight heads was quickly overwhelmed by demand.
- A lot of demand was from people wanting to fit the head to 12mm bearings, especially front mounted bearings.
- The head kit now includes a 12mm top bearing to 15mm mounting adaptor. that allows you to use the Cloudray bracket..
- I step through how the kit fits all types of machines
- The description text under the video lists all the necessary parts required for a total upgrade
- How to use a laser cutter videos
186 The 4th corner Puzzle and Red pointer Lies
- A common problem that many encounter is they can accurately align their ,X and Y and X axes so that the scorch marks are perfect at left back, left front and right front . However, when the move the head to the right rear the scorch mark is SIGNIFICANTLY in error. WHY?
- Many silly explanations have been suggested as to the cause of the problem. They are all fantasy and hope.
- First let’s look at the main laser tube. Despite knowing lots of external dimensional data, I have never been able to perfectly know where the axis of the laser beam is.
- My latest and greatest red dot pointer was yet another “nearly ok” device that was not a good enough replication of the beam path to dynamically set the mirrors . However, it has other uses.
- One use is to discount the idea that the level of the machine is the cause.
- Manhandle the machine and violently lift a corner to prove it had ZERO effect
- The real problem is at mirror 2. The flimsy mirror #2 mounting bracket distorts between the front and rear positions causing the beam to reflect at different angles.
- We create a scorch mark at mirror 3 in the front right position and set the red dot pointer onto that scorch mark.. The red LED beam seems to indicate that mirror 2 is distorting between the back and front position because it is obviously moving.
- However, when we check with scorch marks there is no difference i.e., the red beam is not truthful……in fact misleading.
- I then discuss a common question that has arisen several times. “Can I set the beam from the nozzle backwards?” My belief is “No” and I explain why
- How to use a laser cutter videos
187 Through the lens red dot disappointment
- After the pervious examination of how you cannot make a trustworthy red dot pointer I use diagrams to explain how the slightest amount of axial misalignment robs the red beam if its usefulness for beam alignment.
- Any beam combining system suffers the same problem and must be considered unreliable.
- There is an SPT tube that has a patented integrated red beam combiner that is factory set to the beam.
- Discussion about “though the lens” red dot pointers.
- I have dreamed up my own version of a through the lens pointing system. using steerable red LEDS
- Once designed I then go through the principle of the system I have designed, and it looks like I have designed something that is certain to fail.
- I go ahead and make it anyway
- I totally fail to align it and had to admit that it was the successful failure that I predicted.. It demonstrated clearly that being off axis to the laser beam is always going to end this way.
- How to use a laser cutter videos
188 The 4-inch lens Part 1
- The 4″ lens was something I mounted at the top of my lens tube in conjunction with other low mounted lenses when I was looking for ways to create the smallest dot.
- I am revisiting this 4″ compound idea again after being stimulated by some experiments done by another correspondent, where he was trying to increase the focal range of lenses i.e., less sensitive to going out of focus by the same 4″ compound lens approach..
- Knowing more now about some of the rarely mentioned idiosyncrasies of lenses it made me consider the exact opposite reason to play with long distance compound lenses.. Does CONVERGING the beam through a 4 ” lens onto a 2″ or 2.5″ focal length lens improve its cutting capability?
- Cloudray have sent me several different types of 4″ lens and two 7,5″ focal length lenses YES 7.5″”!!!!
- This is just a quick pathfinder experiment to see if there is any value in pursuing this direction.
- I set up a compound lens configuration and use my focus program to determine the best focus.
- I run a test on 10mm plywood. 10mm acrylic and 9.5mm MDF to compare with previous test data
- There was a 29% improvement with plywood, no improvement with acrylic and 37% improvement on MDF
- What was the magic lens combination? A 7.5″ lens at the top of the tube and a 2.5″ lens at the bottom.
- The net effect of the combination was to SHORTEN the 2.5″ focal length to 44mm from the nominal 63.5mm.
- Was this just a lucky guess or are there better results to be had with other combinations?
- How to use a laser cutter videos
189 Creating the Russ Spec machine part 1
- My China blue machine is in essence a reasonably sound mechanical device. It was cheap for a reason and that revolves around them being fitted with B grade tubes and HV power supplies.
- I claim this is the beginning of the end of my learning journey with this machine because I have made a few significant (but not expensive) design changes to improve usability and performance.
- My final project performance has greatly interested Cloudray, and they are very keen to build and sell Russ Spec machines.
- This video is all about ripping the machine apart, yet again, to replace my acrylic engineering with proper metal parts that Cloudray can manufacture and include on the new machine.
- We start off with a metal adjustable #2 mirror holder that is integrated into a special flexible rack and pinion bracket.
- There is a discussion of the curtains problem and why turning the timing belt inside out solves the problem
- A big chunk of time is spent on modifying the machine to fit the new bracket
- The beam is then reset using the new adjustable #2 mirror adjuster
- With the machine back in working order I use my standard “Foxy” image at 400mm/s as opposed to 200mm/s
- I try running at 800mm/s. Result is a bit fuzzy because I failed to calibrate the scanning offset for 800mm/s and the focus to suit this speed.
- I try running at 1000mm/s with full power and the result , once focused correctly is giving 90% quality image at 12min 43 sec.
- A close-up of the flexible rack and pinion working well.
- Finding that for some reason, 800mm/s produces worse results in 12min 12 sec. about 70%.
- Finally, we test normal engraving at 1000mm/s Pretty good result. on my beer mat card.
- How to use a laser cutter videos
190 Creating the Russ Spec machine part 2
- As part of the Russ Spec machine, we are building a unique one-piece tube mount that integrates a #1 mirror .
- The unit is a very simple laser cut 1.5mm stainless parts that weld together and then assemble into a FIXED position tube holder
- A quick discussion of the design philosophy
- I remove the one-piece acrylic tube holder from the machine and fit the new holder
- We start to reset the beam and demonstrate why this tube mount is used as a simple setting aid for beam alignment.
- Having gone through beam setting yet again I then look at other features I want to see included on the machine
- Ultimate air assist
- Motorized table adjustment
- A tip on how to create your own motorized table for free if you have a manually adjusted table.
- I also have a DELAY OFF timer that switches off the extract fan a few seconds after the end of a program.
- I now unveil the MK2 lightweight head that I will be sending to Cloudray that utilizes the standard 25mm diameter mirror. There are a few changes that I discuss.
- I show how the Mk2 head is manufactured and assembled
- Everything I am designing is attempting to suit 12 or 15mm bearing machines.
- I show hoe simple Z axis adjustment can be.
- I then show an alternative (and preferred) mounting for the front mounted bearing system.
- I try to run fast with high acceleration and fail but I balance speed and acceleration and speed to get optimum performance.
- I need to write a full specification for my dream machine.
- I show how you can assess the performance of your HV power supply
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191 Creating the Russ Spec machine part 3
- I have had second thoughts about how I could make the “airflow management” safe.
- I design and fit a simple steel air inlet duct that allows ducted air in whilst the lid is closed.
- One final wish is to have a side access panel.
192 New parts now available and detailed explanation of beam setting.
- I have designed many parts for my two 300x500mm machines. Over time my designs have evolved and there is a complex set of part combination that could be used.
- I try to unravel that evolutionary story by combining it with a detailed description of beam setting because simplifying that procedure has been one of the main drivers for some of the designs
- A second driver has been to make the machine run faster. However, as I have demonstrated in earlier sessions. short engraving cycle times rely more on rapid acceleration than linear speed in many circumstances.
- I step through the alignment procedure explaining the need to separate beam alignment from the position of the beam on the mirror/ Both are important, but you cannot combine them into one setting goal … they must be set separately..
- After discussing all the various parts I have designed, particularly those that I will be sending to China for the Russ Spec machine, I demonstrate how vital Z beam alignment is
- I show how off angle cuts result from poor Z axis alignment with a practical demonstration..
- I go through the design philosophy and reasons for developing the “flexible rack and pinion” belt drive system
- I finally declare that as I was making parts for my two machines and for Cloudray, I had made a few extras for those that were interested.
- I created an explanatory document with prices in and was also supplying a data pack which included all the dxf files for the parts in case peoples wish to modify or make their own parts.
- How to use a laser cutter videos
193 Beam setting footnote
- I had second thoughts about the offset beam issue (puzzle) that was discussed at the end of the previous video
- I have arranged a crude light bench to demonstrate exactly what is going on when you offset a laser beam
- The answer is simple when you see it demonstrated like this.
- It clearly explains why the offset beam causes off angle cut edges. on thick material.
194 I seem to have lost my FOCUS
- It’s coming up to Christmas at the end of a depressing Covid year, but I am happy to be looking at one of my favourite subjects …..FOCUS
- I keep coming back to lenses because how they work in laser it is a very mysterious subject surrounded by “facts” and myths
- Perfect focus is for visible light cameras and telescope technology. Focusing to a point will be great for engraving …. but for cutting?
- I have spent lots of sessions in my video series I’m trying to understand how lenses work. I know that there are hundreds of years of lens theory development, but I can find no data or research on how lenses achieve the cutting function when teamed up with a laser beam.
- A 2.5″ ZnSe lens is used to carry out my auto focus finding test. at both cutting and engraving speeds
- This demonstrates that the “focal point” appears to be changing with speed.
- Now for one of my illogical and stupid tests. at 12mm below the focal point.
- We get exactly what is predicted by lens theory …. a very thick out of focus line
- However, increase the speed and suddenly, we see that this thick line now becomes a thin line.
- This seems to indicate that despite being grossly out if focus, there is still a focused beam of energy present 12mm below the supposed focus point.
- This is the start of my Russ theory of how lenses cut .
- I present diagrams to illustrate how my “rogue” beam right through the central axis of the lens can cause damage way below the nominal focal point.
- The higher speed filters out the lower power part of the beam (insufficient exposure time to damage the material) but leaves behind an intense central spike of power that does have sufficient exposure time to leave its mark.
- I think I prove there is no single focal point when we use a lens with a Gaussian intensity laser beam.
- I start to dream about the possibility of a long focus compound lens and explain how I might go about improving cutting performance by reducing the beam diameter onto the final lens with a pre-focusing optic.
- How to use a laser cutter videos
195 Honeycomb— A Disaster Looming?
- I am not a lover of the much-used honeycomb table. I have seen too many machine fires caused whilst cutting acrylic.
- Here is a view from inside my machine to watch what happens UNDERNEATH the honeycomb while I cut some acrylic.
- Do not be over alarmed and paranoid about using honeycomb. This is a sober reminder why you should NEVER walk away from your machine whist cutting acrylic.
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196 Long Compound Lens Part 1
- I am a very sceptical and inquisitive person who yearns to understand exactly how things work. At present I do not believe the well tried and tested lens theory explains how our laser lenses cut.
- As prelude to trying to design/discover and suitable lens combination for a long focus compound lens I need to sum up the bits of science required.
- I go through various problems with lens theory that do not accord with physical observations.
- I explain the basic physics of light and the principle of refraction which is the mechanism by which lenses work.
- A reminder of how light waves stimulate molecules to a self-destruct temperature, and it is the INTENSITY of that light which is responsible for the RATE of material damage
- Thus, if we can make a Gaussian intensity beam smaller in diameter, we can increase its INTENSITY. More intensity= faster damage potential.
- Diagrams to show that the projecting focal point/s I am proposing, increase with the lens focal length.
- The reason being to do with the geometry of the lens. Longer focal length lenses are “flatter”
- This is the reasoning behind adding an upper optic to the lens tube to pre-focus the beam to a smaller footprint as it hits the second lens.
- How to use a laser cutter videos
197 Long Compound lens Part 2
- I start off by manufacturing a more sophisticated focus measuring jig
- Using the jig tells me that there seems to be a small discrepancy between the stated focal points and those which I observe.
- We look again at refraction and a property called the refractive index of zinc selenide. That index changes with the wavelength of light
- This results in a shorter focal length (by several mm) when we observe the lens with normal visible white light wavelengths as opposed to the invisible 10.6-micron wavelength light that the machine uses. The machine sees the correct focal length because that is how the lens was designed.
- I check that I am using a 4″ focal length lens by using my jig and then accurately determine the focal point distance beyond the nozzle.
- I set the machine power to about 35watts to replicate a result I discovered on my Tangerine Tiger.
- Using a 25mm square block of acrylic I determine that it takes about half a second to pierce an almost parallel hole right through the 25mm thickness. HOW and WHY?
- Hmmm…. now a silly thought. If I can pierce through that 25mm in half a second, then if I set the speed to 1mm/s I should be able to cut the block in half. Yes, cut through 25mm thick acrylic with 35 watts using a 4″ lens. Sounds impossible but the facts say different.
- Yes, it works. The two halves stick together a bit because of the liquid phase of acrylic flows solidifies in sections of the cut. But it REALLY did cut through.
- I now change the lens to the 7.5″ focal length and carry out the acrylic block test again.
- The results are still staggering
- My first compound lens test was going to be a 4″ lens with a 7.5 pre-focusing lens on top. However, my concern at exceeding the 4″PVD lens energy density limitation made me swap the combination to 4″ lens on top.
- I try to locate the focal point of this combination and WOW, it is no longer 7.5″ but is now less than 2″!!!
- Using my acrylic block test with a half second pulse showed this combination is maybe 30% LESS destructive than either the 7.5″ or 4” lenses on their own.
- STOP! There is something about this result that seems to make no sense.
- There now follows lots of diagrams to illustrate the problem I didn’t foresee. The converging beam of the first lens is pre-focusing and reducing the footprint onto the second lens but because the rays are converging, they are significantly shortening the focal length of the second lens.
- This shorter focal length is DECREASING the cutting ability of the compound when compared to the individual lenses.
- I start REAL cutting tests with 10mm thick poplar plywood as my reference material. I use cutting speed to pierce through at the measure of success.
- Comparing the performance with my previous cutting tests seems rather promising 50 to 100% increase …….very exciting.
- These quick exploratory tests need to be verified and lots more lens combinations explored.
- How to use a laser cutter videos
198 Compound Lens Progress Update
- In the warm office again rather than the freezing workshop.
- Hoping to shortcut a lot of lens combination testing with actual materials, I have designed a simple lens testing fixture that allows me to try different lens combinations at various spacing to determine if there are any obvious pairings that I should carry out real tests on.
- I quickly obtain many promising combinations.
199 Long Compound Lens Part 3
- I move to the workshop to try testing some of the combinations that looked promising during my bench testing of lenses in the last session.
- I test the real focal point of the 7.5″ lens and estimate it to be closer to 9″ and it has a “spot size of about 1.4mm.
- I flip the lens to flat side up and it looks to produce a smaller spot closer to 1mm. but still at 9″.
- I test the 7.5″ lens on real wood, and it performs badly.
- Back to the lens test fixture and I find that the focus happens to be about 7.5″ as expected. Remember back a couple of sessions when I explained about the visible light focal length being shorter than the 10.6 micro focal point? Well, that is what has happened here
- Does this invalidate all the bench tests?
- Looking back at my previous test data, we have a cutting speed target of 14mm/s to beat before we can say we are finding a useful combination
- I receive a delivery of nozzles and lenses from Cloudray just in time to begin testing.
- I abandon my bench test data!!
- I establish a method for testing combinations. First find the focus and then test the cutting speed.
- Lots of random lens swaps tested to gain steady progress.
- How to use a laser cutter videos
200 Long Compound Lens Conclusion
- I have done quite a bit of testing off camera because it’s only the results that are of interest.
- One interesting combination happened to NOT be a long compound lens but a possible alternative for the SHORT compound lens.
- I demonstrate it on my “foxy” picture.
- As I carry on testing in the background my examination of previous test work set minimum goal of 14mm/s . Success means improving that speed.
- Lots of testing with various lens combinations has thrown up an interesting point. I seem to be hitting a speed limit of 16mm/s.
- I did eventually get to 17mm/s but with many combinations (strange?)
- Back to my previous test data to verify that I can repeat the best 14mm/s result with a 2.5″GaAs lens………. because between this testing and the previous test data I have changed my tube. There is little difference in the power, but I need to verify that the previous data still has credibility.
- Testing that 2.5GaAs lens seems to verify consistency. BUT on inspecting the lens I find that the anti-reflective coating looks to be damaged.
- This can only be excess energy density being fired at the lens by relatively short (probably 4”) lenses.
- I find similar damage to a 7.5″ l-ns that was used as a lower lens, Bad news. This means I am really limited to just using a 7.5″ lens as my pre-focus lens
- After lots more background testing, I pull the results together for review against my previous test data and I appear to have made some significant improvements.
- Improvements? The amount of gain depends on how you interpret the data.
- HOWEVER. I had to stop and run all my old tests again because it appears that my new tube is better than the old one and gives better “normal” cutting results.
- I then compare compound results with matching single lens data to see if a 7.5″ pre-focusing lens is improving the performance.
- For certain lenses and focal lengths there are improvements, but the goal is to achieve a combination that gives the fastest cutting performance.
- When I examine all the data for compound lenses a very strange pattern emerges. Regardless of the secondary lens (type, FL, or material) there is remarkable number of results for 17 and 18mm/s. This should not be possible.
- Are there any single lenses that can produce17 or 18mm/s so that we do not need to use a compound combinati0on. The answer was yes.
- This constant cutting speed puzzle caused me to search for reasons why such an oddity was possible. . It forced me to look at the mode burn differences between my old and new tubes.
- They were almost the same power, but the mode burns were significantly different and began to hint at the importance of light INTENSITY (not power) for efficient cutting.
- After everything I have discovered about lens combinations, I must admit that I am hunting for something that cannot exist.
- A failure? Maybe, but every failure has its own teaching. I need to concentrate on understanding he mechanism by which lenses cut. If I can succeed in that, I may be able to decode the puzzles I have seen during these sessions.
- How to use a laser cutter videos
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