A Video Diary: Learning About Chinese Laser Cutting Technology 05

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 tutorials on how to use a laser cutter 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!!!

Russ Sadler - LaserUser Legend Tutorial on how to use a laser cutter
Russ Sadler – LaserUser Legend Tutorial on how to use a laser cutter

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

RDWorks Learning Lab 201 ~

201  The science behind laser Cutting

201  The science behind laser Cutting
  • Any first-time buyer of a laser machine EXPECTS it to cut and without any scientific know how or prior experience they fiddle with a few speed and power parameters, throw a piece of material onto the table , press the start button and a miracle happens.
  • That cutting action is like no other. I demonstrate some mechanical cutting to demonstrate what it is NOT
  • I know of many people that are happy to stay an ignorant expert laser user. However, understanding the very basic science behind damaging material with your laser (cutting or engraving) is one of the first building blocks that helps you to understand how this whole laser technology works.
  • The laser beam is NOT that pink glow you see within the tube. If it was then it would be pink at the front of the machine as well. No, without going into the physics, that pink beam is the “engine” that creates the INVISIBLE l beam of laser light that we use for cutting and engraving.
  • This beam exits the tube and bounces around the machine off mirrors to eventually arrive at a lens that concentrates (amplifies) the light INTENSITY. and reduces the beam to a very small focus point.
  • Now to the science of light (the electromagnetic spectrum), the basic building blocks of ALL materials (atoms and molecules.). the molecular vibration definition of temperature and the coherent nature of a laser beam and how it just happens to be at a wavelength that excites a huge range of molecules. Tutorials on how to use a laser cutter.
  • When the beam of light hits a solid or liquid it encounters SURFACE molecules. The light can only stimulate what it hits. IT does not penetrate into the surface. It stimulates just the surface molecules to heat up and self-destruct (chemically convert to other molecules) whereupon new exposed SURFACE molecules can be stimulated.
  • This light damage is a layer-by-layer erosion process and not something instant. It may appear instant because the more intense the light the faster the erosion will happen.
  • Chemical material damage is one form of erosion but there is another non-chemical erosion . You will be familiar with the solid(ice) liquid(water)and vapour (steam) states of H2O. These changes of state require more and more heat (molecular stimulation) to happen. Acrylic changes state in the same way, at room temperature it is solid. At 160c it becomes liquid and at 200C it becomes acrylic vapour……no chemistry involved. However, heat the vapour and it will change its chemistry and catch fire.
  • A demonstration of the non-uniform light intensity within the laser beam and description of the concept of EXPOSURE time
  • Six flash cards that sum up how a laser beam damages material.
  • A demonstration of how the supposed diverging laser beam below the focal point seems to defy the laws of physics Why no expanding cut?
  • At this point I describe how and why I imagine the beam is cutting below the focal point.
  • A demonstration of a high intensity core to the beam when it is defocused yet lens theory says there should be no power there.
  • Tutorials on how to use a laser cutter

202  More laser Cutting Investigations.

202  More laser Cutting Investigations.
  • A recap on the previous session
  • Another look at the remarkable results from my compound lens tests where despite the focal length of the bottom lens and the spacing from the top 7.5″ pre-focus lens nearly all the cutting speeds were the same at 17 or 18 mm/s.
  • Therefore we must conclude from this that the light INTENSITY through each of these many different lens types must be the same to produce the same amount of damage. How is this possible?
  • Is it to do with the difference between a normal parallel beam hitting the lens or is it caused by the converging pre-focussing lens?
  • Quick mode burn test followed by a comparative burn with a 190mm Fl lens but set 110mm above its focal point to simulate its use in the compound lens tests.
  • This clearly demonstrates that reducing the footprint of a beam dramatically increases its intensity and damage capability.
  • I wondered if I took two matching lenses placed flat sides to each other and with a special spacing between, could I make a parallel input beam exit as a smaller parallel output. Theory says yes but in practice it failed.
  • I carry out a series of cutting tests to see if I can find any useful patterns that may guide my thinking.
  • Just going round in circles, I conclude I must be trying to look at lenses in the wrong way. Just measuring their cutting capability sounds logical but is very one dimensional. Tutorials on how to use a laser cutter
  • I write a new lens test program based on DOTS and DOT MODE. The aim is to standardize the cutting parameters for lenses. I use the same power for every test and a series of fixed exposure times. Measuring the depths of cut for each exposure time will produce a cutting profile for each lens.
  • With the focus set to the top surface of a special test block I run a test on a 4″ lens. The data in this format is not easily understandable so the penetrations were plotted graphically.
  • When we examine the graph, it becomes obvious that I only need to see a small part of the graph to represent the performance at REAL cutting speeds.
  • The same 4″ lens is used to cut a 25mm square and then measure the block and the hole to calculate the cut width,
  • A 4″ graph is used to find out how long it takes to pierce 10mm deep. The kerf width is used to build a series of touching holes (kerf diameter) to fit into 1mm.
  • This allows me to predict a cutting speed for 10mm acrylic with this lens. The speed is about 5mm/s. In practice 5mm /s was easy and it just about made a cut at 6mm/s. This may prove to be a good cutting speed predictor (for my machine only).
  • I run a whole series of similar tests on all my lenses and then examine the graphical results.
  • I then chose the best performing 1.5″ lens and added the 7.5″ lens above it to see how the combination performed the same test. This clearly shows no difference
  • A similar no benefit result for compound lenses also existed for the 2″,2.5 and 4″ lenses.
  • I then use the graphs to see which lens focal length I should use to cut 10mm thick acrylic for example. Now comes an interesting observation The longer the focal length the quicker it will cut.
  • This kills the myth that you need more power to use a 4″ lens.
  • We have finally proved no benefit for having a compound lens.
  • Tutorials on how to use a laser cutter

203 The Russ Theory of Laser Lenses Part 1

203 The Russ Theory of Laser Lenses Part 1
  •  Having found a reliable way to characterize the performance of each lens by using acrylic, I would not expect to see the same performance figures in other materials. Other materials such as plywood and MDF are not transparent so the same test regime would not work
  • Or would it? With a little lateral thinking I have devised a slightly less accurate version of the same test that will allow lens characterization for different opaque materials.
  • I select the best performing lens from each focal length and test it with wood so that I can get material related relative performance data.
  • There are a few surprises when we compare the performance graphs for wood and acrylic
  • Using the best performing cutting lens (a 2.5″ GaAs) I then attempt to use these charts to predict the cutting speed for various thickness of materials. I devise a fairly crude method for converting the chart data into cutting speed.
  • Then I cut 3mm Baltic birch ply and then 9mm ply to test/refine my formula.
  • I then make a quantum leap to 26mm thick oak (maybe elm). I use my formula to predict a cutting speed of 3mm/s WHAT!!!!!…… with only 65 watts and a 2.5″ lens. That’s insanity on steroids!
  • Don’t fall off your chair when you see the prediction happen in front of your eyes.
  • Much more important…. look at the straightness and squareness of the cut. That poses some serious questions about how is this possible?
  • I then examine under a powerful microscope, two extremes of my “pierce tubes” from long and short focus lenses and discuss why and how the different burn patterns could be formed.
  • Finally I hint that I have now worked out exactly how lenses do the things I have demonstrated. I plan to keep it a secret until the next session. I have a wife that tells me “I knew that anyway” when she is struggling with something, and I help her out. With that lifelong experience, I challenge those that think they already know the answer to speak out now before I tell them in the next session………just because it appeals to my sense of fun.
  • Tutorials on how to use a laser cutter

204  Laser Beam Safety

204  Laser Beam Safety
  • This is an unplanned session interrupting my research into how lenses cut. I have had run of questions about expensive safety glasses.
  • Safety glasses salesmen play on your fear of the word LASER and how such dangerous equipment will easily make you blind.
  • I cannot give you any advice as to how to best spend your money. Instead, I plan to show and demonstrate all the dangers of this machine and assess the risk factor of each. At the end, I hope you will be able to make a sensible risk-assessed decision for yourself.
  • A brief description of the INVISIBLE laser beam and how it bounces around the machine off 3 mirrors and is finally amplified through a special lens.
  • Lasers are classified in 4 groups. 1 being safe and 4 being very dangerous. I demonstrate what a class 4 laser can do
  • Some science follows. the laser beam is a beam of invisible LIGHT it is NOT a beam of HEAT.
  • You all know what sound waves are and look like, well, light is the same sort of wave energy but instead of what we hear being at about 15thousand cycles per second, the frequency of our invisible laser light is about 28 thousand billion cycles per second (unimaginable.!!!) Tutorials on how to use a laser cutter
  • I try to make these numbers into something tangible with a simple table, jelly, and cake analogy. This helps to explain the concept of how waves of energy can shake different materials in different ways depending on the internal structure of the material.
  • The next bit of science they don’t teach at school is the fact that all atoms and molecules are vibrating, and the rate of vibration defines the molecules temperature. Make a molecule vibrate faster and it gets hotter.
  • It just so happens that the 28 terahertz frequency of our laser light is just about the right frequency to excite most material molecules, causing them to vibrate faster and thus get hotter.
  •  The lens makes the laser beam hundreds of times more intense. Thus, at the focal point that intense light causes damage almost instantly
  • I use water to demonstrate how concentrated light energy can create steam as it stimulates water molecules to get hot. Water looks transparent to our eyes but to the laser beam it is totally opaque. It is therefore only the SIURFACE molecules that are being stimulated and instantly tun to stem. There is little or no heating of the water mass itself.
  • You also think of glass and the plastic lens of my glasses as being transparent. To us yes but they are solid opaque materials to our laser beam.
  • Co2 laser light has a relatively long wavelength of 10.6 microns. The light only sees 3 things in its universe 1) metals. All of which reflect the light (used for mirrors). 2) A very small group of salt-like materials that are transparent to the light (we use these for lenses) and 3) EVERYTHING ELSE.. whose molecules will be excited (heated) when the 10.6-micron wavelength light hits it.
  • The beam that travels around the machine is not dangerous unless you put yourself directly in its path. If a bullet misses you by half a millimetre, it’s not dangerous. It only damages you if it hits you. There are no sideways rays that “leak” from that invisible beam NOTHING will jump out and bite you.
  • The only stupid thing to do is place metal in the path of the beam because the be could be reflected at YOU
  • I demonstrate that glass and polycarbonate spectacle lenses 100% absorb the laser light because they are group 3 materials. Thus, simple industrial safety glasses costing $2 will afford your eyes 100% protection against being hit by a laser beam.
  • I then demonstrate cutting/engraving organic materials (wood, MDF, leather etc). The very bright intense light you see is a much greater danger to your eyes. It is just like looking at a mini arc welder. It contains high levels of UV light which can damage human cells (including eyes) and its intensity is a bit like looking at the sun
  • I speak of the relative risks for each of the subject discussed
  • Don’t fear this laser technology. Understand it and respect it.
  • Tutorial how to use a laser cutter.

205  The Russ Theory of how Lasers Lenses Cut Part 2

205  The Russ Theory of how Lasers Lenses Cut Part 2
  • My recent failure to find a long focus lens to improve cutting efficiency led me to look differently at how I could characterize lenses.
  • The method I devised revealed some great patterns when displayed in a graphical form
  • We go back and review all the basic lens theory that I had been indoctrinated with. I point out some major problems with that theory that I discovered when I tested the cutting performance of a variety of lenses
  • I look at the properties of a Gaussian distribution and how it is used to describe the light intensity within a laser beam and how power and intensity are separately described by the same graph.
  • Amplifying the beam through a lens does not increase the POWER it only increases the INTENSITY of the light.
  • Analysing how the beam intensifies according to spot size theory, again produced this crazy result that was opposite to my observations.
  • There was another problem that didn’t make sense. Just how was it possible to cut the correct size holes through thick material. You set the focal point onto the material surface but what happens below that focal point is beam DIVERGRENCE and LOSS of energy density. This is well described by conventional lens theory. So how is what we witness possible?
  • I quickly go through a huge, documented data set from my previous cutting tests to illustrate that whatever the focal length, cutting through 10mm material produced PARALLEL sided cuts.
  • I show more of my puzzling tests with straight “worm holes” in acrylic below the focal point
  • Are those holes the result of “total internal reflection” of laser light? No.
  • I try to “see” the shape of the damage patterns below the focal point by making test burns in clear acrylic for different lenses
  • I then compare the graphical data that characterizes various lens focal lengths and it suddenly begins to show a pattern that I first suspected 2 years ago. The cutting depth INCREASES with the focal length for a CONSTANT power input
  • This explodes several myths and “facts”. You do not need high power to use a 4″ lens. You cut with INTENSITY and not POWER, so the spot size/power density idea is incorrect.
  • I then summarise a revised list of truths that form the basis of my theory.
  • I present diagrams of lenses and discus the various ray patterns and how refraction affects the path of the rays.
  • We then concentrate our attention to what happens to rays JUST a fraction away from the lens axis. It seems that the geometry of the spherical surface is so close to being NORMAL to the ray path that only the merest amount of refraction will occur. That means that the focal point of these near-axial rays will focus way beyond the nominal focal point of the lens.
  • This PROJECTING focal point/s provides a carrying (and focussing) path for that central Gaussian intensity.
  • The double refraction path of a plano-convex lens when used flat down produces a narrower range of focus scatter. Used flat side up that focus scatter is much greater because there is only one refraction occurring.
  • This points to the fact that a plano convex lens will produce more efficient cutting if used flat side up……. this is against all conventional wisdom. However, examining my lens cutting data confirms that flat side up produces deeper cutting for ALL focal lengths.
  • HOWEVER. …….All these results and conclusions are caveated by one special condition. If your raw laser beam is non-Gaussian then you will not be able to achieve efficient cutting.
  • Tutorials on how to use a laser cutter

206  Experiments to Test The Lens Cutting Theory

206  Experiments to Test The Lens Cutting Theory
  • Some people did not fully comprehend my theory of how lenses cut so I recap with a revised diagram
  • I re-run the test of cutting through 26mm hardwood with a 2.5″ GaAs lens at 3mm/s
  • I then change the setup by removing the hardwood but leaving everything else set the same but this time burning a track on a piece of so that its surface mimics the BOTTOM surface of the hard wood We are trying to see what the beam is like at that point
  • By changing the speed, we can filter out the lower power from the outer part of the thick beam
  • I then demonstrate that a 4″ lens will cut through the 26mm hardwood but at 2mm/s i.e., 33% less speed….but why.
  • I examine the reflections off the curved surfaces of various lenses to assess the degree of curvature. The flatter the lens surfaces the greater the “projected” focus (according to my theory) and it illustrates why the 2.5″GaAS cuts better than the 4″ ZnSe.
  • I take a less than perfect lens and test it with my penetration test. We then begin brutally modifying it in stages. I test at each stage to assess the performance change. Eventually I drill right through the axis and destroy the cutting ability
  • I finally test this non-cutting lens to see if it will still focus and engrave.
  • Important safety warning about working with zinc selenide.
  • Tutorials on how to use a laser cutter

207  The Importance of Beam Intensity

207  The Importance of Beam Intensity
  • You have only one machine and 1 tube’s worth of experience. Most of you will not have power tested your tube or even be aware that most of the Chinese laser tube market is dishonest.
  • What is a laser beam supposed to look like and how to test what you have?
  • I can guarantee that your eBay or Amazon Marketplace will be fitted with a B grade or almost junk tube. Many of those tubes will be labelled K H Laser and that will be an absolute guarantee of a factory reject that has been relabelled
  • The premier grade Reci tube named in an advert is not always what it seems and because of their high cost I spend some time pointing out that the market is flooded with B grade Reci tubes and how you can recognize them.
  • Can I cut twice as fast if I double the power of my tube? No, and I explain why the beam DIAMTER is an important factor.
  • How is beam diameter defined? here is a brief explanation
  • And why beam diameter is an important element in determining INTENSITY
  • We look at two mode burns from the same tube just a few moments apart. Why are they so different?
  • What is BEAM DIVERGENCE? It is a little discussed feature of all laser beams. It is typically about 3mm/m beam growth for all glass tubes. That means the beam is one diameter at the back corner of the machine and a much bigger diameter at the diagonally opposite front corner.
  • Remember, the power remains the same, but the beam diameter grows thus meaning that the INTENSITY drops and cutting ability is seriously affected.
  • This session has been about the raw beam before it passes through the lens. If the intensity is low to start with, amplifying it through a lens will improve it… but not very much. As the saying goes “rubbish in= rubbish out”
  • Tutorials on how to use a laser cutter

208  Can I Remove the focal point?

208  Can I Remove the focal point?
  • My theory of lenses is based on reverse engineering. I try to theorise what happens in a lens to cause what I observe.
  • My observations lead me to believe that a lens has two distinct characteristics. One is an engraving capability and the other a cutting property.
  •  We have been educated to understand that lenses focus light to a single point. Set that focal point onto the surface of material and it will do damage i.e., engrave. . But if that is where the light energy is focused how is it possible to cut deep narrow parallel slots?
  • The best example of something being wrong with this idea is my demonstration of cutting 26mm thick hardwood with a 2.5″ lens. Am I contravening the laws of physics? I doubt it
  • From all my lens work so far it has become very evident that beam intensity is a crucial factor in the cutting process. I look at why it is possible to cut above expectations if you only have a low power tube.
  • In a recent session I was brutal with a lens and drilled a hole through its axis. I did this to prove my theory that cutting was a function of something happening very close to the lens axis. That hole destroyed the lens’s cutting capability
  •  That hole did not affect the engraving capability, so that seems to prove my point about two very separate capabilities.
  • In this session I will try the opposite experiment i.e. I will try to leave the lens cutting capability but remove the engraving property.
  • I do a couple of control tests on the lens before I start modifying it i.e. a focus test and depth penetration test
  • We then proceed to modify the lens in stages and document the performance after each change.
  • I complete the lens modification and test and graphically present the results
  • I have ground away the outer parts of the lens in stages until there was only a 3mm central disc lens surface remaining. This was able to cut but unable to engrave because I could no longer find a focus point at or near 38mm.
  • I think this reliably proves my two separate functions idea, but I will carry out further detailed experiments in future sessions to examine the functions more closely.
  • Tutorials on how to use a laser cutter

209     Cutting With a Projected Focus – Final Proof

209     Cutting With a Projected Focus – Final Proof

During the past few sessions I have been trying to prove that there is something other than the traditional focal point that is responsible for the the cutting behaviour that all lenses exhibit. The commonly held view to date that the increased focal range that happens as the focal length increases is somehow responsible for that cutting depth increase.

This is transparently illogical when you see me cutting 26mm deep hardwood with a 2.5″ lens. That lens has a focal depth of less than 2mm!!!!.

I have developed a theory based on observation and reverse engineering that explains what ACTUALLY happens as the laser beam passes through a lens and after several sessions of experiments and tests I have demonstrated the credibility of that theory.

This session finally demonstrates that removing the central axis of a lens has no impact on its engraving properties. I also prove that removing those engraving properties still leaves a lens with cutting ability and that cutting ability comes from a second thin axial beam that focuses at some point beyond the normal focal point. It is this “leakage” path that allows a thin focused beam of intense light to damage material BELOW the focal point.

  • Review of the previous session and the belief there are strange things going on with lenses
  • Reverse engineering from workplace results to determine what must be happening within the lens.
  • Using the Compound Engraving Lens to assist in the evaluation
  • Setting the compound lens focus and carrying out penetration tests
  • Discussion about default settings in RDWorks
  • Comparing a good 38.1mm lens results against a 38.1mm lens that has a hole drilled through the centre
  • Discovery that using the compound lens with two “holed” lenses makes little difference to the results obtained with whole lenses.
  • Discussing the method of making good dots / dashes (sausages)
  • The process of printing sausage shaped dots
  • Examining the results under a microscope
  • Printing the fox image with the compound lens using 4 options of 2 x whole, holed and whole, whole and holed, 2 x holed and comparing results.
  • Normal focal point versus projecting focal point
  • Investigating the projecting focal point
  • Looking at the 300ms mode burns
  • Tutorials on how to use a laser cutter

210   Lets Focus on Focus – Again!

210     Lets Focus on Focus – Again!

The dictionary describes a focal point as that place where parallel rays of light passing through a lens are refracted to converge on a single point. That may apply to visible light for cameras and telescopes where light sources are uniform and lenses are high precision and usually multiples, but in the world of Chinese lasers things are a long way from that dictionary definition.

The use of a single lens and then a choice of just two forms, plano convex and meniscus, is the first disadvantage. The simple spherical geometry of these lens forms will never achieve that dictionary perfection. The longer the focal length of the lens, the greater the imperfection. The single feature that ALL lasers beams posses is a non-uniform intensity profile.

The perfect laser beam will conform to a Gaussian intensity distribution. ( a bell shape graph) where the central light intensity is many times greater than the outer regions of the beam. Combine the focussing weakness of spherical lens geometry with the non uniform intensity within the laser beam and we no longer have that idealized model of focus that we are all taught.

We set the focal point for a lens to that distance where we create the smallest burn spot or the thinnest drawn line. This is not setting the LIGHT focal point but that point where the the light INTENSITY is sufficient to damage the material we are marking/cutting . I clearly demonstrate that the traditional model of focus is of very limited value in our weird world of lasers.

  • Review of previous lens findings
  • The two distinct characteristics of a lens
  • Analysing what the correct focus point of a lens is.
  • Lens placed curved side up, gives a smaller spot size
  • Where is the focal point as specified by the manufacturer?
  • Flipping the lens so that it is curved side down, lengthens the focal position.
  • Why we get a range of focal distances when we change the speed – Dynamic Focus
  • 2″ + 2.5″ Gallium Arsenide (GaAs) lenses considered the best for laser cutting
  • Theoretical minimum spot size
  • Using Manual Set+ and Laser Set+ on the keypad
  • The effect of exposure time on spot size
  • The effect of power on spot size
  • Evaluating the results
  • 20ms, 50ms & 100ms burn durations
  • Hole size vs burn size vs scorch size evaluation
  • Running dynamic focus tests at 80mm/s and 99% power
    • Running the same dynamic focus tests at 400mm/s changes the focal position by 1mm (shorter)
    • Flipping the lens, changes focal position by about 1mm
  • There is no light focus, but there are numerous power focal levels
  • Power filtering by using exposure time.
  • Tutorials on how to use a laser cutter

211   Understanding Black Etching Ceramics – Part 1

211     Understanding Black Etching Ceramics – Part 1

The popularity of the 450nm blue diode laser has created a lot of interest in etching images onto ceramic tiles. There may be similarities between the physics/chemistry of this new technique and the Laser Tiles that I tested about 3 years ago, but I was never able to decode the vital facts that underpinned the Laser Tile magic.

With several failed emulation attempts in my history book , I lost interest about a year ago. However, my new enthusiasm for this subject has been prompted by people wanting to add a CO2 laser machine to their hobby inventory after starting small with a blue diode laser.

I keep being questioned about whether the CO2 laser can perform this same black etching onto ceramics. The 450nm wavelength light has significantly different capabilities to the 10,600nm CO2 wavelength, so there is no simple yes/no answer I can give. I have already demonstrated failure, but now there are a few more clues that I can examine from the successful diode laser method.

Anyone familiar with my learning journey will realize that I will not be interested in a tedious hunt for parameters that may or may not be there. I need to understand the mechanism that allows the blue diode to be successful at this task. Only when I possess that knowledge will I be able to answer the question.

Tutorials on how to use a laser cutter

212   Understanding Black Etching Ceramics – Part 2

212     Understanding Black Etching Ceramics – Part 2

In the previous session I discovered how white titanium dioxide powder becomes black solid. In this session I attempt to discover if it is possible to make precision black dots from this process.

If you understand the fundamental principles of photo replication with a laser engraver, then crisp black dots on white ceramics promises the possibility of a new era of precision in CO2 glass tube laser engraving. It may also mean no special photo preparation software will be needed.

Tutorials on how to use a laser cutter

213   How Lenses Cut – More Experiments

213     How Lenses Cut – More Experiments

The facts so far in this saga point to one or more focal points below the nominal focal point. This appears to be the reason that lenses can cut material. However, there are some obvious facts that indicate that my interpretation of the evidence is either incorrect or maybe only part of the total picture.

This video analyses the experimental data is a detailed way that casts a wider light on this subject of how lenses cut. Tutorials on how to use a laser cutter.

214   Setting Z to a new Zero Position

214     Setting Z to a new Zero Position

With the luxury of a stepper controlled Z axis, I have always wanted to be able to quickly set the table to a different position and to set that position as Z=0 . There are a few ways to achieve this on a standard machine but all are rather tedious. In this session; I show how to modify your machine to make setting Z=0 instant and at any table level.

Tutorials on how to use a laser cutter

215   At Last! I Understand How Lenses Cut

215     At Last! I Understand How Lenses Cut

I have struggled for 2 years to understand why conventional lens theory does not match the observable experimental laser cutting data. This session uses my new set of gallium arsenide lenses to create data sets from a mix of new and old experiments.

Reverse engineering the ray paths and integrating my knowledge of how and why mode burns produce their erosion shapes, has allowed me to create scale CAD drawings for each of my 4 lens focal lengths. The end result is that my theory about projecting focal points below the normal focal point proved to be correct … BUT is only a contributing and limiting factor for the cutting action that we observe.

Damage to materials with light energy is totally dependent upon light INTENSITY ( some call it energy density) which my new model includes. However, the conventional lens theory models that you will encounter make no mention of this fact as you will see in the links that follow.

Here are links to credible sources that try explain how and why to use different focal length lenses but all are basing their messaging on standard white light visible optics lens theory (ray tracing).

American Photonics https://www.youtube.com/watch?v=ykZSc…

Trotec https://www.youtube.com/watch?v=K_dKU…

Universal https://www.youtube.com/watch?v=ykZSc…

Epilog http://support.epiloglaser.com/articl…

Tutorials on how to use a laser cutter

216   The Focus Fallacy

216     The Focus Fallacy

When you buy a lens you have to believe the manufacturer when he defines its focal length. We can only buy two lens material types for our machines. Zinc selenide and gallium arsenide.

It is possible to crudely verify the focal length of a ZnSe lens because you can see through it. However it will only be in the ball park with normal light because the real focal length is different at at our invisible laser wavelength and that will be how the lens was designed.

No that is not the fallacy.

There are many videos on Youtube showing you ways to find the focus . Very few people realise that they are not finding the lens’s fixed focal point but something else.

This session proves that the manufacturer’s focal point is nothing more than an imaginary value as far as our technology is concerned because we can change parameters and influence its position.

Tutorials on how to use a laser cutter

217   Do laser lenses meet specification?

217     Do laser lenses meet specification?

My recent understanding of the mechanism by which laser beams cut, has had knock on effects that help solve other issues that I have been struggling with. In particular I have never been able to get even close to the spot sizes claimed for various focal length lenses.

I have known for many years that the idea of a fixed focal point for our laser machine lenses was a myth but never understood why. It is easily proven that changing speed or power can affect the “focal point”, thus proving it must be something other than a light ray focal point which is fixed when the lens is designed.

With my new found knowledge of the cutting mechanism, I now understand why the spot size and other claimed lens properties are so exaggerated and impossible to achieve. A normal light beam carrying image information can be manipulated and tamed by one or more lenses, however, although a laser beam obeys the same laws of physics, the peculiar non-uniform INTENSITY within the beam exploits weaknesses inherent within the spherical lens design.

Tutorials on how to use a laser cutter

218   Old Light through new windows

218     Old Light through new windows

This is a short video to introduce a new condensed series of videos for newcomers to the laser community. The videos are not machine or software specific but are aimed at teaching the science basics, the machine basics and the fundamental principles behind the many processes that are possible with this technology.

I am sure there will be material in here for experts as well as beginners. Tutorials on how to use a laser cutter.

219   Lenses and laser beams laugh at lens theory

219     Lenses and laser beams laugh at lens theory

This is the final session of my mission to understand how laser beams and lenses act together to circumnavigate the well established rules of lens theory.

It was obvious 3 years ago that something illogical was occurring because so many of my tests and experiments were unexplainable by the disciples of lens theory. With only two grey cells, a cheap Chinese laser machine and a plethora of optical ignorance, I was obviously well qualified to solve a problem that everyone else seemed to be ignoring for the past 60 years.

I could clearly demonstrate that there was some sort of secret love affair between lenses and laser beams that was allowing them flout the norms of conventional geometric optics. One of my early engineering mentors taught me that ignorance and intelligence are vital problem solving tools and that reverse engineering a problem can often lead you slowly back to the source.

After 3 years of nibbling away at the problem, my perseverance has now been rewarded by a recent lightbulb moment that enabled me to visualize the mechanism by which the unique properties of a laser beam allow it to have its own secret relationship with lenses.

This video attempts to share that secret by piecing together a series of demonstrable concepts that build to help YOU visualize the final mechanism. No laws of physics are broken but the optics industry seems to have ignored these weird properties that are beyond the scope of conventional lens design.

Tutorials on how to use a laser cutter


220   The Cloudray Russ Spec Prototype

220   The Cloudray Russ Spec Prototype

After many months of waiting, despite Covid 19 slowing things to zero at times, Cloudray have delivered on their wish to manufacture a small format, well specified laser cutting and engraving machine.

With just a couple of videos and some sample parts I sent them to upgrade a basic machine, the team at Cloudray have succeeded in replicating my much-modified China blue machine. As you will see from the video they succeeded….plus some.

This is a pre production prototype that was sent for me to critique, so, as you would expect from me, this is an honest review of their success so far.

Tutorials on how to use a laser cutter

222 Beam Combiners: A New Approach

222 Beam Combiners: A New Approach

I looked at the performance of beam combiners more than 4 years ago and decided then that it was impossible to set them with any precision. Of course I have managed for 6 years without one and at the last review, I power tested before and after to find a 5% power loss. However, this was a heavy premium to pay for an unpredictable indication of where the beam would hit your work.

Cloudray are most insistent that a beam combiner is the only way to provide a “red dot” for the lightweight head on the Russ Spec machine they have produced. I found myself with a dilemma… agree to shipping a high spec high quality machine with a piece of known substandard kit or design a replacement that would do the job properly.

I accepted the latter challenge and this video is an an analysis of the task to be performed and then testing the design that I created.

Tutorials on how to use a laser cutter

223 Air Assist Why, How and When

223 Air Assist Why, How and When

There are many myths and misunderstandings associated with air assist.

Does more air pressure mean a deeper, faster or cleaner cut?

Efficient cutting requires a “sharp” laser beam intensity profile. A “blunt” beam will still cut but much slower and with more collateral damage such as scorched top corners and dark/burnt edges. I cannot test for those conditions because I have sharp beams on my machines.

Because of my advantage, it is possible that I will not see the gains that others claim from more powerful compressors. This was supposed to be more of a demonstration session to share my experience but as I was demonstrating I saw new possibilities for improving the engraving air assist.

Oh dear, I feel another design project awaits with these Tutorials on how to use a laser cutter.

224 Blue Dream Begins it’s Test Work

224 Blue Dream Begins it’s Test work

Although my Russ Spec machine arrived several weeks ago, updates and modifications have prevented my from using the machine in anger to see how it compared with the original China blue that it was emulating. In reality it is a better quality machine but the anticipated performance needed to be verified. Only a few key tests were required to assess performance, so this is a mixed bag of testing and using the machine to explore the properties of Borax as an engraving enhancer. At the same time it was an opportunity to test my new design of engraving air assist.

225 Is a Beam Expander useful

225 Is a Beam Expander useful

All laser beams have divergent properties and that causes the peak INTENSITY of the beam to degrade with distance. INTENSITY is a vital requirement for efficient cutting. Thus a diverging beam reduces its ability to cut the more it diverges. If you can optically correct the divergence then you have a beam with constant cutting properties.. Sadly, lens theory tells us that you have to EXPAND the beam diameter to control its parallelism. That increased (blunter) beam is fine for engraving but degrades cutting ability. In this session, my optical engineering naivety allows me to ignore the theory and see if there is a practical way to collimate the beam with no loss of cutting ability.

226 Can my Beam Collimator Work

226 Can my Beam Collimator Work

After some crude experiments with lenses in the previous session, I settled on a promising configuration that seemed to allow me to control beam divergence. The main goal for me was to try and control the 7 mrad beam divergence on my RF machine. With a claimed beam diameter of 2mm and 30 watts of power, this machine could turn into a CUTTING monster if only I could keep that 2mm beam parallel and retain its Gaussian intensity profile over the table area. I modified a redundant X3 beam expander to perform proper evaluation of my test configuration. My acquired knowledge of how laser beams have no respect for lens theory meant I was entering uncharted territory. Pre-testing established it was possible to control beam divergence but could I retain Gaussian intensity?

Tutorials on how to use a laser cutter

227 Cutting 40mm Polyethylene Foam

227 Cutting 40mm Polyethylene Foam

About 3 years ago I used DOT mode to cut shapes in polyethylene foam packing material. It was not entirely successful because the bottom of the cut opened up with a significant taper. My previous attempts were based on the traditional approach of experimenting with parameters to try and find values that minimised the taper. During that intervening period I have come to understand fully the relationship between the laser beam, the lens and the way light interacts with materials. I no longer randomly hunt for successful cutting parameters but start off by trying to understand the properties of the material. From there I try to zoom in on lens and beam configurations that are sympathetic to the needs of the material. This is a fairly quick revisit to cutting PE, to see if my new knowledge can help decode the cutting mechanism that causes PE to cut in such an uncontrolled manner.

228 Search for a Beam Collimator Part 1

228 Search for a Beam Collimator Part 1

With advice from a guy commenting on my recent failed attempt to create my own X1 beam expander/collimator, I have been persuaded to revisit the X2 beam combiner I currently use on the RF Tangerine Tiger machine. He provided suggestions that had been successful for him, on how I may be able to improve the performance of that X2 device. Followers of my journey will know of my mistrust of lens theory when it comes to mixing laser beams and lenses. This is yet another example of how lens theory may work perfectly for imaging but does not work for damaging. This is an exercise in lens juggling and disdain for conventional optics. However, in parallel with this personal effort, I have challenged several global optics companies selling beam expanders, with this problem. Much as expected the silence has been deafening.

229 Search for a Beam Collimator Part 2

229 Search for a Beam Collimator Part 2

I am attempting to upgrade my 30watt RF machine into a 60 watt cutting machine without spending any money. A Coherent 60 watt equivalent would cost about £6000 . My knowledge of laser beams and how they work has allowed me to look at this 30 watt RF unit with a fresh pair of eyes. I have a 70 watt glass tube machine that has a beam diameter of about 8mm and it is a super all-purpose machine with great cutting ability. When I look at this RF unit the beam exits the source as a 4mm beam,. which means the beam has an incredibly high light INTENSITY. Intensity =rate of material damage. The greater the intensity the faster material damage will occur. The beam intensity of this 30 watt tube is greater than my 70 watt tube purely because of the beam diameter. It therefore has the potential to cut better than my 70 wat tube IF I can find a way to keep the beam at 3mm diameter throughout the work area without losing that INTENSITY. Experts tell me that failure is a certainty.

Tutorials on how to use a laser cutter

230 Cutting 40mm Polyethylene Foam

230 Cutting 40mm Polyethylene Foam

My quest is to find ways to improve the cutting performance of this 30 watt RF machine Now that I have finalized the beam profiling I imagine will work, testing lenses can begin to see how they react to the ultra small beam I have produced. Optical theorists tell me that my approach will not produce the rewards I dream of. Right or wrong. I must pursue the research I have started to find out for myself if theory has nailed everything down. Are there treasures to be found?

231 Search for a Beam Conditioner part 4

231 Search for a Beam Conditioner part 4

Although I have managed to condition the output laser beam so that its original diameter and intensity are projected into the work area, the amazing cutting potential have not been realized. I accidentally discovered that it does fantastic things for engraving provided i use a compound lens but that was not my objective. This session is all about trying to decode why that super high intensity is not being amplified as it passes through a lens. Tutorials on how to use a laser cutter

232 Beam Expansion Means Degraded Cutting

232 Beam Expansion Means Degraded Cutting

Demonstration trumps any theoretical argument. I have long been fascinated by the supposed “magic” of RF laser technology. The prohibitive cost of those masterpieces of engineering can only be justified by industry or a small business. About a year ago I decided to build my own budget version by modifying a cheap Chinese glass tube machine with a 30 watt RF laser source. It did not take long to find that there was no “magic” to this complex technology after all. I tested and experimented for a few months before consigning the machine to a corner of the workshop where it remained unused for almost a year. With just 30 watts it was very poor at cutting and although the machine was capable of engraving at 1500mm/s, the 30 watt power limit meant that 500mm/s was the real ceiling. In the meantime, research with lenses and my glass tube machines allowed me to discover the importance of light INTENSITY for cutting. Purists will claim light is something you see and energy density is a more correct term….sorry, not for me. I gravitated back to the RF laser source when I realized it possessed an incredibly high INTENSITY small diameter beam. However an RF laser beam diverges at about 7mm/m and as the beam diameter grows its intensity decreases. To make the beam diameter uniform across the whole work area and optical device called a beam expander does exactly what it says . It takes the diverging small high intensity beam, and increases it to a larger diameter that can be optically tuned to virtually parallel. Sadly, this increase (as mentioned previously) is at the expense of light INTENSITY. Less intensity is still fine for engraving but crucifies cutting potential. Once that INTENSITY has gone it cannot be recovered. Putting the remaining intensity through a lens will amplify it BUT you cannot amplify what’s not there. Thus any RF source with a beam expander (and that means all those expensive machines!!) will be very inefficient at CUTTING. The fix is easy………. throw more watts at the problem ( if you have LOTS more $)

233 More Small Beam Experiments

233 More Small Beam Experiments

I freely admit to being a mechanical engineer that has no right to be dabbling in the well researched 3000 year old science of lenses. I keep being told by those well versed in this subject that the smallest focal diameter will be achieved when I use the maximum diameter of lens available. In my case that means expanding a naked 3 mm 30 watt output beam by at least a factor of 4. I can fully understand how and why this works just fine for creating a concentrated focal spot for engraving but my experimental work and vandalism of lenses indicates that an engraving focus is not a cutting focus. Thus I am fascinated by the very small very high intensity beam I have managed to project into the central area of my worktable. Previous quick exploratory tests indicate that there is a very weird relationship between this very small beam and lenses. In this session I try to examine that relationship in more detail with several comparative experiments. Tutorials on how to use a laser cutter

234 Small Beam Glimmer of Hope

234 Small Beam Glimmer of Hope

Despite advice to the contrary. I am not yet giving up on my quest to make my 30 watt RF laser perform the same cutting tasks as my 70 watt glass tube machine. At this point, I appear to be proving the sceptics right but this session is one where I take stock of the data I already have and examine some of the “interesting” observations. This leads me to a investigate a totally illogical set of new conditions that shows promising results.

235 Small Beam and Long Focus Lens Incompatible

235 Small Beam and Long Focus Lens Incompatible

I started off this project trying to create a small high intensity raw beam onto my work area. For 80% of the work area I succeeded but then discovered an unexpected problem. Lenses could not focus this small intense beam. So this project has now developed into one of investigating just what it is that prevents lenses from amplifying my very small unusual beam of energy.

236 Powder Coating with your Laser

236 Powder Coating with your Laser

I have been sent video links of people using plastic powder coating materials to colour fill deep cut wood engravings. Hmmm . Their results look OK from a distance and yes the idea is perfectly logical. Add heat to plastic and it melts (provided you are not too enthusiastic). Having been a user of the powder coating process for many years, I understand how it is designed to work…..and wood is not on that list of suitable materials. This is an investigation to see if the process is really viable and what parameters, if any, should we be using. Could it be extended to other materials?

237 Black Marking Stainless Steel

237 Black Marking Stainless Steel

It must be 5 years since i looked at this subject the first time. During that time there have been just one new marking ink and Cermark and Thermark are now integrated to one product. All these products are expensive (and good) but the cheaper alternative has always been spray-on Molybdenum Disulphide. Some claim it is far inferior and it is possible that the perimeter range for these alternative products may be narrower. This session investigates the chemistry underpinning this technology and tests novel products that posses the suspected chemistry for success. To make things fair and comparative I use the same lens, power and speed settings throughout.

238 The ULTIMATE A to Z tutorial of beam setting

238 The ULTIMATE A to Z tutorial of beam setting

I recall the uncertainty I felt the first time I removed a mirror 7 years ago. Would the machine ever work correctly again?. Over an 18 month period I kept purposely upsetting my beam alignment in an attempt to understand the logic behind setting the beam perfectly and soon discovered that Chinese machine designers either didn’t understand the process or purposely made it difficult for “non-professionals”. I suspect my first assumption is correct and naïve machine design is responsible for the MANY different beam alignment strategies people have proposed to overcome the mess Chinese designers have created. This session deconstructs beam alignment and machine design. I have modified my machines to make beam setting simple with a series of logical and progressive actions that guarantee setting perfection. I have tackled this subject several times over the years but never in such all -encompassing detail. As a young design engineer I was taught that “you must understand the problem before trying to design a solution”. It seems that very few people really understand what they are trying to achieve with beam alignment beyond making sure the beam passes through the nozzle.

239 RF laser CAN do high speed photo REPLICATION

239 RF laser CAN do high speed photo REPLICATION

After a break for other projects I am back investigating the properties of a super high intensity small diameter 30 watt RF CO2 beam A long time ago i had established that setting my cheap Chinese 5030 RF machine to run at 1400 mm/s was a waste of time because the 30 watts of power was unable to support normal engraving at more than 500mm/s and photo replication was near impossible, even at 200mm/s. By removing the commercial X2 beam expander and replacing it with my on beam “conditioner”, allowed me to project the 3mm beam exiting the tube tube through to the middle of the work table My initial experiments with lenses showed an unexpected inability of lenses to focus this small high intensity beam to make it a CUTTING monster. However, the geometry of very short focal length lenses showed hints of focussing ability Putting the CUTTING dream aside I have done some more experiments with various compound lens configurations to see if I can exploit this high intensity beam in a different way …..for high speed photo replication.


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