20 – 20W MOPA Fiber Laser: Photo Engraving on Slate (58:26)

0:01 welcome to another fiber laser learning lab no i’m not in the wrong place

0:07 and you’re right this is not a fiber laser machine but today um we’re going to do a little

0:15 bit of an investigation because i had a problem just recently as i mentioned in my other series my

0:21 stepdaughter is busy building a small business um with this with this

0:26 particular machine and uh she’s been engraving some slate

0:32 and i thought hang on the fiber laser does slate very very quickly this machine does it

0:39 moderately quickly now that i’ve pimped it up but surely we must be able to do a much

0:45much quicker job on the fiber laser machine i’m lost for words really because

0:51the fiber laser machine has got a spot size of about 0.06 or better

0:58this has got a spot size of about 0.1 so technically

1:04i should be able to run this slate on that machine over there much faster

1:10and with better quality i’ve been doing a little bit of fiddling behind the scenes fish very quickly

1:19and i can’t succeed now question is why can’t i succeed and that’s what we’re going to have a

1:25look at today first of all we’re going to have a quick run on here and see what the quality is and what the dot is that

1:31i can produce on this machine for dithered engraving and then we’re going to take a look at why

1:36i can’t achieve the same results on the fiber laser because i know that i can engrave slate on the

1:42fiber laser it does a fantastic job of engraving text but text is not the same as precision

1:49dots and that’s what i’m trying to establish just what it is i mean i’ve tried all

1:55sorts of parameters on the fiber laser machine so the only way to check it is to find out what dot i’m able to

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

2:02produce so first of all let’s just have a look at the results i get from this machine

2:12there’s 254 dots per inch or 254 pixels per inch on the image

2:23[Laughter]

2:34no [Music]

2:40i think you’ll agree that’s a pretty good image now i don’t need to run that image on

2:46both machines what i really need to do is to check the quality of the dots that i’m producing

2:53on this machine with this lens at this focus so we’ll just change the program and we’ll

3:00just run my little dot test [Music]

3:07okay it’s as simple as that so just so you can see where it is look there is

3:12the little dash and dot pattern here’s what it looks like at 50 times

3:19magnification there’s a scale on this side here which is in point one of a millimeter and if i move that down

3:26onto there we can probably just about see 0.1 of a millimeter

3:33so these dots are about 0.1 of a millimeter diameter now they’re 0.2 millimeter pitch so it begins to make

3:41sense that we’ve got dots there that are about 0.1 and 0.1 allows me to generate a picture

3:48at 254 ppi or 254 dots per inch

3:56now if we move off the dots we’ve got single dots there same sort of size and then we’ve

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

4:03got these dashes now the various size dashes we should find that the dashes are 0.1 wide

4:10and it’s much easier to see them we can see that they’re roughly 0.1 but

4:15what you can’t see there at that magnification is actually what’s going on

4:21there we go i think we might have found something there now first of all you can see right along the center there is a sort

4:28of a groove okay it’s not uniform all the way along but that is the very high

4:34intensity part of the gaussian focused beam and on the side here

4:41what we’ve got is something that probably i would imagine is like a

4:48an eruption from a volcano we’ve purged out the middle and we’ve

4:53blown it up onto the sides but what we need to do is just go in and

4:59look at that at a higher magnification and then you’ll see what’s actually happening now first of all we’ve got our

5:05deep groove and if we look in the bottom of the groove there’s a hint of what’s

5:10going on down there but when we come up to the top of the groove just there

5:20can you see all these bubbles that are existing along the side here

5:27now those bubbles do not exist in the background and they’re obviously

5:33also a different color so what’s going on

5:38well this is slate and slate started off its life as sediment in the bottom of an ocean

5:46sediment sand silicate of some sort anyway

5:55it gets compressed into a very dense material it gets subducted below the earth’s

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

6:01crust compressed so some fantastic pressures and then over millions of years it works

6:07its way back up to the surface of some sort of mountain or hill and gets thrust up above the sea level

6:15and that’s how they managed to dig slate out of the sides of mountains

6:21but the essence of it is it starts off life as a sort of a sandy silicate material and what do they make

6:28from sand and silicates glass what we’ve actually done here

6:34we’ve fused the material together and we’ve produced a glassy structure and that’s what those bubbles are those

6:41are bubbles in a gooey glassy material that we’ve created when we heated the

6:48surface up so that’s not a white powder that’s actually

6:53a completely permanent glaze gray glassy structure

6:59now there’s a classic example of a single dot and there you can see the bubbles of the

7:06glassy structure within that dot here we are on the fiber laser machine

7:11and we know that one micron wavelength light is basically not going to pass through

7:17this material it’s opaque and opaque basically means let me give you that simple analogy that i mentioned

7:24to you before that when a stone falls from the sky it’s completely harmless

7:30the only time it’s dangerous is when it hits you on the head and at that point when it collides with

7:36something solid you get an energy transfer okay the same applies to a light wave

7:43when the light wave comes down here only when it hits this solid surface will something happen

7:49and one micron waves are adequate to vibrate the molecules in the surface

7:56of this material and cause them to heat up so

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

8:01we know that the light is going to work on here can we get the energy concentrated in

8:08such a way that we can do my little dot test for example

8:14technically we should be able to do it because the focus on here is better than the focus

8:20on the continuous wave laser machine now that’s really the clue that gets me

8:28started on what the parameters should be for this machine now this is a 20 watt fiber laser and as

8:35i mentioned before we used about 20 watts when we were doing the

8:41test here and this little pattern just here

8:48so here’s the little dot program and what we’re going to try and do is to simulate the same conditions that we had

8:55over on the glass tube co2 laser so we’re trying to achieve that with a speed of 400

9:02power 100 percent the frequency here doesn’t really matter because we’ve got it set to a thousand but it’s going to

9:08be ignored because what i’ve done i’ve set the pulse width to one nanosecond now one nanosecond is a

9:15special code for this machine which basically switches on continuously as cw mode which is

9:21equivalent to the glass tube laser so we’ve got an equivalent set of conditions here

9:27for the 10.6 co2 laser and now we’re going to see if we can simulate the same sort of results on this fibre

9:35laser we’ve got a little pattern what we need

9:41to do is go and look at that under the microscope to see what we’ve got well here we are at 50 times magnification

9:47and we’ve got a scale here which at 50 times magnification shows that we have got

9:52a line which is roughly 0.1 millimeters wide so it’s doing roughly the same sort of

9:58job as the co2 laser it’s not getting any better i hoped it might be a little bit better

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

10:05but in fact let’s just have a look at the dots as you can see the dots are there but they’re pretty

10:11indistinct they’re merging into each other because the power down the center here

10:18has exploded so much that the glass that’s been created around the edge of

10:23the volcano has spilled over and joined the next dot it gives the impression

10:30that i’ve actually got too much power there at 20 watts and maybe i’ll be able to

10:36control these dots much better if i start reducing the power so this is a very good start previously

10:44any work that i’d done on this machine just by eye had been based on

10:50using one of the pulse widths that were available on this machine i hadn’t used this continuous wave mode

10:59well at 80 you can see we’re getting we’re still getting the glassy effect we’re getting slightly better

11:06separation of the dots they’re not spilling over quite as much as they did before

11:11and that’s 80 percent so let’s take a look what 70 looks like

11:20it’s getting a little bit better we’re seeing a little bit of better

11:25separation 70 percent let’s try 60

11:31still rather messy isn’t it they’re not really dots there are holes there but there are not clean dots

11:39let’s try 50 percent still a bit messy we need to go back and just remind

11:45ourselves so that’s what the co2 laser was doing

11:52i mean they’re not exactly 0.1 dots but they’re getting close they’re about 0.12

11:58because they’ve definitely got a gap between them but also they haven’t got a hollow

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

12:04center so maybe we could back off on the power even more or possibly

12:12lift the focus right up by maybe 10 or 12 millimeters so that we’re only using the tip of the

12:21high energy part of the beam so we’ve still got another couple of

12:26things we could try

12:42i think you can already see at those settings there is no comparison

12:49fiber laser is relatively rubbish in relation to the co2 laser

12:56the previous one was done at 100 power and 2000 millimeters a second

13:02because i don’t think the speed has any effect on it at all the pulses are still there

13:07at the same power regardless of the speed this is not like metal where you’re trying to build up the heat

13:13you just want the power per pulse and as we switch the beam on the power

13:19is there instantly we’re going to run this now at 30 percent power and see what effect that has

13:35we’ll give it one last shot at 60 power and we’ll go back to 400 millimeters a

13:41second just so that we can say we’ve given a fair comparative shot there is no point

13:46in coming onto this machine and doing it at 400 millimeters a second because i can do it on my other machine at 400

13:53millimeters a second so there’s no advantage to going down this route

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

14:03well yes it’s better [Applause] and if you didn’t have anything to

14:09compare it with i suppose you’d think that was quite good but when you see what the co2 laser

14:14can do this is still rubbish as we mentioned earlier just look at the definition of hairs

14:21all the fur on the co2 one what have we got on this one

14:29nothing just a bit of a blur now just in case you think i’m giving up too easily

14:36um i’ve also tried playing with the focus so those people that think they’re putting the uh putting the thing out of

14:42focus when they lift it up by two or three millimeters are sorely mistaken because look i’ve raised the

14:48head up in other words i’ve put the focus down below the focal point

14:54but this is not a reflective material so let’s not get too concerned and i’ve actually dropped the focus 22

15:01millimeters below the focal point by the time i get to here and yeah it’s it’s a very slightly

15:09blurred but we’ve still got sufficient power in the center of the beam to actually put a reasonable mark on

15:17this slate food for thought focus is not what you

15:22think it is stop it’s another day

15:27i’m older i’m grayer i’m fatter and i’ve had a thought i was just about

15:35to say that this machine can’t do this sort of work

15:40and then i it just doesn’t make sense it’s got all the capability to do the

15:46job but somehow or other it’s not giving

15:52i think in reality it’s me not understanding i suspect we have a little bit of a

15:58problem here number one i understand what I’m trying to achieve

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

16:05you might not so therefore what i’m going to do i’m going to take a break here and

16:12we’re going to go back to the beginning and try and explain to you the basic theory behind photo engraving

16:20on these laser machines because in essence it’s quite simple when you

16:26understand it but it’s a bit like riding a bike if you lift your feet off the ground

16:32you’ll fall over you need to do a bit more than lifting your feet off the ground many years before photography became available

16:40newspapers could only print text black ink on white paper this became a

16:47problem when they wanted to put pictures into their newspapers the only way that they could generate

16:54pictures was like this they had to get copper plate scribed and filled with ink

17:03so they could get their black ink onto white paper now that’s an artist’s job a very

17:10skilled job to do that so it was quite a few years before they managed to

17:16solve this problem and create ways of breaking up that picture from

17:23a continuous analog scale which went from very dark brown nearly

17:29black to almost white it’s a sepia

17:34it hasn’t got a complete black and white color range but it’s got a very wide color range

17:40there are just gradual changes of tone across the whole of the picture so somehow they had to

17:45break that image down into black and white now there are many many early attempts but eventually they

17:51came up with a process called half tone printing half tone printing allows you to break that picture down

17:58into a into a selection of dots this whole principle of half tone

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

18:04printing relies on your brain being fooled and filling in the gaps between the spaces

18:13it does basically a color mixing of black and white into various shades of

18:19grey within your brain so depending on the size of the dots

18:24that you’ve got in the black the black gradually changes to a sort of gray

18:31and then the gray the mid grays here change to white as the black gets less

18:37and less that is a very crude representation of what the half tone printing principle is

18:45the problem with that when we try and apply it to our laser system we’ve got small black dots and we’ve got

18:51big black dots now the only thing that we can do with the laser machine is make

18:57dark spots or we can burn something into the surface of a material we can

19:02only create one color generally now a couple of the large industrial type laser machines base their photo

19:10engraving software on this principle but it has a major weakness

19:16you can’t produce different size dots on a laser machine sounds pretty obvious

19:22doesn’t it but before we get on to the details of that this picture here

19:28although it’s an analog picture has been reproduced in modern times to go onto a computer so

19:34therefore it is no longer an analog picture and if we zoom in on this you can clearly see

19:42that it’s not completely analog it’s digital it’s made up of little

19:48square blocks called pixels and this is the modern way in which photographs and

19:55images are stored and used now isn’t that amazingly detailed what

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

20:00i’m going to do is we’re going to analyze this picture to try and illustrate several points first of all i’m in

20:07photoshop here and it gives me the opportunity to find out exactly how this picture is constructed

20:13if we take a look at the top here we’ll find that the picture contains a total of 21.7

20:18million pixels of those little squares that we just saw now you can’t see any squares on

20:25there can you if i zoom in there we go look you can see the pixels there at the moment it says this

20:32resolution of this picture it looks a stunning quality picture is

20:38300 pixels per inch i wonder what happens if i change that resolution to 10

20:46pixels per inch do you think the picture is going to get

20:51better or worse there we go

20:57trust me i’ve changed it i’ve cancelled it and we’ll come in and we’ll look at the image again image

21:04size 10 pixels per inch 21.7 million pixels still

21:12the same number of pixels that we started off with the only difference is if we look here

21:20at the width of the picture it’s now millimeters 8790

21:29millimeters eight meters wide and five and a half meters tall

21:36let’s just change that back to 300 where it was ah where is the eight meters gone

21:43it’s now 293 millimeters the very important point i want to make

21:48here is that pixels are not fixed elements a pixel can be as big as your

21:56imagination i could have a pixel that is a meter square

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

22:03you would see that picture from 10 miles off probably

22:08it would still have 21.7 million pixels but the pixels would be huge if you got

22:16up close to it you would not be able to see what the image was the bigger the pixels

22:21the further away you have to be to see the image so by that understanding if you’re only going to

22:28look at it at arm’s length you need a high resolution image but if you’re looking at as a billboard for example

22:34you could find that the pixels on a billboard might be one millimeter square if you walked up close to it so that’s

22:41important feature number one pixels are as big as you want them to be okay we will come back to that one

22:47shortly because that’s an important feature when it comes to deciding what we’re going to do with our images here

22:54we’ve got a colored image now we can’t work with colored images on our laser machine because

22:59we’ve already decided we’ve only got two opportunities we either burn or we don’t burn

23:06we’re effectively doing the same as an ink image black or white

23:13white is nothing and black is ink on a background

23:19so the first thing we’ve got to do with this image if we want to use it for laser printing is we’ve got to

23:26take away the color and turn it into something called grayscale okay discard the color

23:33information and now we’ve got a grayscale image now grayscale is an interesting point

23:40because unlike cpr images they run from black

23:45to white and there are no steps in between it’s all completely gradual with

23:52the grayscale system black is defined as number zero

23:59and white is defined as two five five well there’s 254 shades of grey between

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

24:05black and white so there’s a total of 256 colors in the range every one of these has a

24:12different color a different shade of grey each one of these little squares has got a different number attached to

24:19its color and every one of those pixels is mapped into something in machine memory in your

24:26computer memory although we’ve got individual blocks pixels there on that screen

24:32we can’t work with them because we can only produce black and no black i.e white

24:40there is a different sort of half tone printing it’s something called stochastic half tone which is basically

24:47random half tone this is patterned half tone printing where you’ve got a

24:52regular pattern and different size dots now stochastic half tone printing is exactly

24:59the opposite to that and let me just show you i’m going to first of all take this

25:05image and i’m going to turn it away from being a grayscale image into being something called a bitmap image

25:12now the resolution i’m going to leave it at 300 at the moment pixels per inch and we’re going to use

25:17something here called a diffusion dither we just say okay

25:22i’ve just destroyed the image well no i haven’t not really what you see there is something called

25:29an aliasing pattern it’s the mixing of the pixels that are in the background of the image

25:35with the pixels that are on the screen that you’re seeing as i change the magnification look it goes back to normal so if i zoom

25:43in now we’ll see what’s happened

25:50every one of these pixels that we can see here is either black or white we can now work

25:57with this on our laser if we just consider one of those lines across there look we can scan across there and

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

26:05here we are we can turn the computer on and we can burn a black line we can turn the computer off nothing on black line off nothing

26:13on off on off and that’s the way the image is sent down from here

26:20to your computer just a series of on off signals that correspond with the

26:26morse code that you see on the screen so it’s really very simple

26:31the problem is the size of that pixel what is it well remember what i said

26:38that pixel can be as big or as small as you want if i made that pixel for instance 100

26:45millimeters square could i print it with a single dot

26:51no obviously so in essence what we’re saying here is the size of the dot that we can produce

26:58with the machine it controls the resolution of our image the

27:05resolution of our image is controlled by the size of that pixel that single pixel there so

27:12if the smallest dot that i can produce is naught point one millimeters

27:20there will be 10 of those dots in a millimeter

27:26and there will be 254 of those dots in an inch so therefore what i’ve now

27:32got to do i’ve got to come back to this image and i’ve got to set the image size to

27:41254 now it won’t change anything on this screen

27:47but what it does it changes the physical size of the pixels and it will actually change if we take a

27:54look again and if we look again you’ll see that first of all it’s changing the number of

27:59pixels and the resolution is 250 poor 254

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

28:05but the size of the image now is 219 by 346. now

28:12if we don’t want an image that size then we’ll have to change it

28:19so now i could if i wanted to click these boxes to constrain the image and let’s just say i wanted an image

28:25that’s 100 millimeters wide 120 millimeters wide 120.

28:32there we go so i’ve got 120 wide 75 millimeters tall and it’s still got

28:38254 pixels per inch i have not changed the resolution of the picture

28:45okay and you’ll notice the number of pixels has now dropped even more

28:54and that’s an image which we can print because a we can produce dots that are

29:000.1 millimeters diameter and b it’s a size that we can get onto

29:07the machine okay so what you’re looking at here is a

29:12very crude representation of my little dot test pattern

29:19now it’s been very carefully designed this test pattern for several good reasons first of all i want to be

29:25able to visibly quickly check the size of a dot estimate the size of a dot

29:31so i’ve made my pixels here not 0.1 millimeters wide the gap between the pixels is also 0.1

29:40millimeters wide so that’s effectively a black pixel a white pixel black pixel white pixel

29:48like that so all these are black these images that i’ve got on here the

29:54way your laser interprets these is very simple it comes along here and it gets to this

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

30:01point just here and it switches the laser beam on and it draws a burn line until it gets

30:09to here and then it switches off because when there’s white

30:15there’s no laser beam on off on off the same applies to

30:22all of these they’re all on for black and off for white but there’s a fundamental

30:27problem here we can’t first of all manufacture square pixels

30:32with our laser we can only produce round burn dots and there’s another problem

30:38when the laser comes up to this point here it says switch the beam on which it does

30:43instantly but of course we’ve got a round dot it gets to this point and it says switch

30:50off but again we’ve got a round dot here here on

30:58off on off now it might not seem too much of a

31:03problem to you along there because there’s still dashes but hang about that dot

31:11is half a pixel hanging off the end and we’ve got one pixel gap here so if

31:19i’ve got half a pixel there half a pixel there half a pixel here

31:24and half a pixel here like that with my dots

31:33then how much gap have i got between the pixels

31:38um that’s a problem because remember how the brain is working it’s looking at the overall color of the

31:44background which is white and it’s looking at the overall color of the foreground which is black

31:50and it’s mixing those two together in your brain so the more white in the image

31:57the lighter the gray you will see and the more black in the image the

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

32:03darker the image will be do you see the problem we’ve lost our

32:09white between the pixels so we’re automatically when we’re doing

32:14photo engraving where we’ve got lots of these pixels sitting very close together we’re automatically going to create a

32:21dark image and that is why you will find with every single piece of photo engraving software

32:29there is a fairly significant chunk of lightening or brightness control involved to try

32:36and enhance the image and reduce this effect i have to admit to being

32:43slightly very slightly involved with some of the early development work in another piece

32:48of software called light burn very clever guy

32:53designed the software and he’s done a fantastic job of replacing virtually every part of rd works and

33:00making it five times better than it ever was with all sorts of extra features

33:06he identified this problem and decided that the right thing to do would be to delay the start

33:14of the beam so he shifted the start of the beam along and finished the beam half a pixel

33:21early and half a pixel late so that now

33:26you get the start and the finish of your pixel at the right place the problem is

33:33when you subtract half a pixel off of there and half a pixel off of there

33:38you’ve got no pixel so you get no dot and that was a fundamental fault

33:45with his logic everything that was a single pixel

33:50disappeared and it changed the quality of the image

33:56completely the opposite way to what was intended you will always have this issue and you will always have to

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

34:02lighten your picture now this 0.1 dimension for this pattern has been very carefully chosen based on

34:10what we could possibly achieve on a co2 laser with the lens system there you can get

34:16less than 0.1 dot under certain circumstances with certain materials but in general

34:21the smallest dot you’ll be able to burn will be 0.1 and therefore the best resolution that

34:29you can create your image at is 254

34:34ppi which is a 0.1 resolution pixels per inch

34:41equals 25

34:460.4 millimeters so if we’ve got 0.1 it means we’ve got

34:5310 of these pixels per millimeter so if we multiply 10 by 225.4 we get

35:00254. so that’s how we arrive at these numbers now good quality photographs are

35:06typically 300 pixels per inch

35:12the essence of what we have to do to copy that photograph is to make sure that we have dots

35:20that are 0.1 so we can get 254 dots per inch so that we can immediately

35:27copy every pixel with a dot that’s a very key part of photo engraving you can’t

35:35make the dots bigger than the pixels because if you do they will overlap like this and they will occlude

35:43the background which is the thing that’s giving you the impression of light and dark you

35:49change the density and the color of your image

35:55i did say that it was very simple and i did say that it was very complex this is the

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

36:01complex part this is the simple part very simple one dot equals one pixel

36:09so look at the other way around decide the size of your dot and that will tell you the resolution of

36:15the image that you can reproduce pixels do not overlap on the screen

36:21therefore you cannot have dots overlapping on your material

36:27now i did say that i would come back to this image here which as you can see it quite small you

36:32can see that it runs from black grey through to white and we did say that some of the big companies use this

36:40idea for their photo engraving it’s quite economical on code

36:47but it’s not particularly pretty as an end result it gives reasonable results but not

36:53quality results in my personal opinion there are people that claim they can print

36:58a thousand dpi now a thousand dpi

37:03means we’re going to have a pixel or a dot size of .025

37:10that’s about the thickness of a human hair that’s pretty incredible nobody in the

37:16normal world can produce dots that small with an industrial laser machine or even one of these hobby laser machines

37:24the best you’re going to be able to do is probably 0.05 which is probably close on 500 dots

37:30per inch but let’s just assume that they think they can do a thousand

37:36dpi well if this is a if this is one dot you won’t see it

37:42three or four dots then you might see it because what happens is it’s going to take a huge amount of time

37:48at a thousand dpi because what happens is you’ve got a thousand dots across this way

37:54and therefore you must have a thousand dots down that way because this is a square pixel

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

38:01and a thousand lines this way is going to take absolutely ages to scan backwards and forwards these

38:08blobs will be built up from these very very small dots that they supposedly can put down

38:15so it’s going to take a huge amount of time to scan across this image but very very quickly we’ll just zip

38:22back to this lovely image here which is the grayscale image now it is

38:27possible to try and work with a grayscale image depending on the material that you’re

38:34working with for example an organic material such as wood or leather has got a

38:43scorching range from very light scorching to burnt dark brown

38:51so there is a color range that you could exploit to try and match the 256

38:59shades of grey that are in this image and what that means is instead of

39:04putting dots down dot dot dot all of the same intensity what you would

39:10try to do is every time you moved across a dot you change the power

39:16in the pulse so it is possible to do grayscale engraving as well

39:25but it’s nowhere near as clean neat and efficient from everything that

39:32i’ve tried and tested as proper dithered binary engraving

39:39but i thought i’d just mention that hey that’s not the be all and end or what we’re trying to achieve

39:45but of course on things like slate where we’ve only got one color gray

39:51and a background which is dark grey if you’re using acrylic you produce

39:57white on a clear background so what i’m saying is there are many

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

40:03materials around which are what i call binary materials they’ve only got two natural colors

40:08anyway it’s only the organic materials where you’ve got a possible color range that

40:14you can exploit to produce grayscale engraving right back at the machine

40:20let’s try and make some sense of what we have observed earlier under the microscope now i was trying to

40:27run at 2 000 millimeters a second because as i said to you this machine is incredibly

40:33fast at the way in which it builds up its pulses unlike the co2 the pulses will happen

40:39instantly to travel one millimeter takes roughly half a millisecond

40:45and that’s just a starting point to make life mathematical life nice and simple a little bit later on

40:52we’ve got a two nanosecond pulse now that means we’re going to get a

40:58pulse every roughly micro second i know it’s 850

41:03rather than a million pulses a second but hey let’s not argue too much about that amongst friends for rough maths it’s good enough

41:10to say a million pulses a second now our pixel is only 0.1 millimeters

41:17wide it might only be 0.1 millimeters wide but as far as this machine is concerned

41:23it’s a long line it’s a line that is 0.1 millimeters long so how long does it

41:30take to travel 0.1 millimeters the answer is

41:350.5 milliseconds divided by 10 because there’s 10 of these in a

41:41millimeter so that means it takes 50 microseconds

41:46to travel one pixel but we’re producing a million pulses a second so therefore it’s

41:54burning 50 times across that 0.1 millimeter pixel but we’ve already

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

42:01determined from our observations under the microscope that when we fire the laser at this slate

42:09it produces a little volcano which produces when i say a burn spot i mean a damage

42:15zone of 0.1 millimeters that’s a rather familiar number 0.1 millimeters that’s the size

42:22of a pixel but hang about we’ve just talked about that 0.1 pixel

42:28with a 0.1 dot means it’s going to stop and hang over the end of each pixel

42:35by half a dot and isn’t that what we observed we observed all the dots joining up

42:44so we’re never going to win with this approach because we’re always going to have this

42:51half a pixel overlap it doesn’t happen on the co2 machine for various reasons the most obvious is the

42:58fact that we don’t get this first half dot overlap because there’s

43:03always a delay in the pulse build up something that i’ve noticed a long time ago and never had any occasion to use it

43:10want or if you like be curious about it is something here called drill mode now that sounds

43:19interesting doesn’t it drill mode i’m wondering if i’ve got any control

43:25between drill mode we’ve got 0.1

43:30milliseconds set by default milliseconds that sounds like

43:38years in terms of the response speed for this machine

43:44so yeah i thought well maybe 2 000

43:51yeah 2 000 millimeters a second how long a pulse do i actually need

43:57and i played with the numbers and i finished up with something like .0005 or something like that

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

44:03some some stupid number of milliseconds

44:08did it work no absolutely nothing

44:14[Applause] back to the drawing board that was a dead end

44:21not wishing to give up on this i felt that somewhere on this machine there must be some way

44:29of doing what i need to do drill mode seem to offer the most

44:37likely possibility so i went to the manual and tried to understand how

44:45drill mode worked now the good news is

44:53it’s something to do with scan mode which is great so it’s not mode on its own

44:58you can actually use it with scanning and here it is 0.1 default

45:06milliseconds select this mode to define in microseconds

45:17hang on that said milliseconds

45:25now it begins to make a bit more sense i was putting such a short pulse in that

45:32i was getting nothing out so if it’s actually micro seconds

45:37i was putting in like nano seconds of pulses which are not going to do me any good at

45:44all because they’re not repetitive they’re just once

45:50well how once are they

45:57select this mode to define in micro seconds how long the laser is kept on for each point

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

46:04of the image that is marked i wonder what that means that sounds

46:10very chinglish to me

46:15and then we come on to the obvious some materials require longer and shorter exposure times to achieve good marking well yeah

46:26increasing the drill mode time will sometimes create a deeper but lower resolution mark hang on

46:34lower resolution prolonged drill mode times will

46:39significantly increase the overall time required to complete the mark so

46:46that seems to imply that there’s no relationship between speed and drill mode

46:53i can specify two thousand millimeters a second but i’m not gonna run at two thousand millimeters a second i’m going to run

47:00at and here’s where i think the trick comes in look

47:08fixed dpi well i’ve already got the dpi fixed for my images

47:13i’ve fixed in x 254 because that’s the image i’m fixed in y

47:20254 because that’s what my image is

47:25so i think with a nearest bit of luck when i now interpret

47:32this this is what i think i’m going to get

47:42i think by specifying 254 ppi which is a fixed interval in x and 254

47:50ppi fixed increment in y i’m actually defining my pixels to sit

47:57on a grid like this and if

48:02my pixel sits on the intersect of one of these grids and is black remember what black does

48:10black turns the beam on so if i specify a duration time

48:15for drilling i’m going to get

48:20at that intersect a drill hole and then i’m going to get another drill

48:27hole there and there and there and that means when i get a

48:33single pixel i’m not going to get a lump out at the end i’m going to get a drill hole at the intersect point

48:42wow now this is looking very very i’m getting quite excited now is it too

48:48good to be true let’s give it a try i presume that the

48:53pulse and frequency numbers are still relevant to the

48:59drilling pulse itself so if i specify a two nanosecond pulse i’m going to get a pulse every

49:05microsecond just one two nanosecond pulse so if i

49:11specify one microsecond i’m only going to get one two nanosecond pulse

49:18and hopefully it’s going to be one two nanosecond pulse right in the middle of a pixel well as i’ve said to you

49:24before ah this is not a tutorial this is you looking over my shoulder

49:32and either falling flat on my face or succeeding so let’s push the button and see what we

49:41[Applause] get

49:47something silly for a minute because i think i’ve got to go the wrong way i think i

49:52want to go shorter time period but i’m going to go a longer time period just to prove a

49:59point [Applause] to starting

Transcript for 20W MOPA Fiber Laser: Photo Engraving on Slate (Cont…)

50:06wow yes you see it took a lot longer

50:13so it’s not speed related it’s duration of pulse related

50:19[Applause]

50:25you will absolutely love this when you see it under the microscope

50:30now we’re going to go the other way

50:37[Applause] 1.5 straight to point one let’s do that just

50:44go too far right down to point one micro seconds

50:54now that was quick to be honest what i can see here is really exciting

51:02[Applause] certainly quick again

51:11and look at those under the microscope now because they are far too interesting for me to keep to

51:16myself here’s what 10 micro seconds of drilling

51:22looks like now do you believe that this process produces glass is there any more

51:28proof that i need look at it

51:41in fact i accidentally touched that with the microscope and look i’ve cracked the glass okay now let’s take a look at

51:48the next one which was one microsecond

51:54okay now look we can see the set of holes along the dashes there

52:02they’re literally just piercing holes they’re not running along continuously

52:08wow you see at one micro second we’re starting to see the dots but

52:14they’re still squirting out enough glass so that they overlap

52:19we’re going to go down to 0.5 microseconds

52:27and the dots are a lot cleaner

52:36now we’re getting a bit of separation between them look

52:42we’re still squirting out too much from the little volcanoes

52:49so we’re still putting too much energy in let’s go and look at the point

52:56one microsecond everything is getting a lot neater isn’t

53:01it look we can see every one of those pulses along the dashes here

53:09i mean it clearly indicates that we have got drilling taking place at the coordinate intersects

53:17as my drawing indicated wow look at those they’re lovely dots

53:23aren’t they well now i say they’re lovely dots there is a problem with them actually

53:33they’re nice size and they’ve got a nice white edge to all those dots they’re

53:40lovely and separated they will produce a great image i’m absolutely sure about that

53:46in fact i’m sure it’s going to actually beat the quality of the image that i get from the co2 laser

53:55but and there is a butt

54:01look at this can you see that there

54:06a black hole it’s a donut but it’s not a white doughnut it’s a

54:11black doughnut now remember the way in which the whole of this principle

54:19of photo engraving works it’s the relationship between white

54:25and black so here we’ve got a background

54:30and here we’ve got if you like a white foreground but we’ve also got some black background

54:36showing you no no no i know it’s not the background but it doesn’t matter what it is it’s black

54:42so it’s adding to the blackness of the image

54:48so it’s actually going to downplay the quality of the result that we get

54:53it’s going to be a slightly dimmer result now i don’t

54:59i didn’t realize that when i was looking at them under the magnifying glass but we also did a

55:05couple of other trials and i might have to go and do something did i do i changed the power didn’t i to a different different power setting

55:14yeah no that’s not going to work is it because look i’ve got even bigger black holes in there

55:20[Laughter] now i know this is a very minor detail

55:25that probably most people wouldn’t even bother to think about but it is an important part of viewing

55:32these images it’s something that i’ve become very very aware of and those holes are just unacceptable

55:38there’s all black and no white decreasing sorry by increasing the pulse length i’m just making the hole bigger and the

55:45squirt the white glassy effect less so let’s just move on to the next one

55:53which was a 2 nanosecond pulse but at 80 percent power

56:02now will that reduce the central black part well

56:10it certainly looks as though it’s having an effect but has it made them so

56:20and looking at those you know i think they are less than 0.1 in fact i can see they’re less

56:27than 0.1 they’re probably somewhere in the region of about 0.08

56:32one inch is 25.4 millimeters 25.4

56:38divided by 0.08.08

56:43equals 317.5 i might set the resolution to 300 and

56:49see what we get well i’m extremely pleased with that result and

56:57yeah okay egg on me face i thought it was going to fail it hasn’t it’s come up trumps so let’s

57:04go and do the real test which to see what the image comes out like in comparison

57:19well that’s probably about half the time that it takes to do on the co2 laser

57:25even though i’ve got my co2 laser well pimped up and i thought it was doing

57:31very well this is doing a superb job it’s really quite interesting that

57:36when you look at the actual door mouse itself it seems to be slightly darker than this

57:44one which one do i like it’s very difficult to choose between

57:50them to be honest this one’s slightly whiter dots in the

57:55center of the little spots that’s what i think is making this

58:01one darker but it’s still a lovely image

58:07well i think we’ll finish on that happy note should we i think we found the secret of um

58:13engraving slate on the fiber laser drill mode thanks for your time and

58:19patience and um I’ll see you on another adventure next time bye for now