19 – Grayscale Laser Engraving

0:01 welcome to another session with my little tangerine tiger here um

0:07 today we’re going to be working with grayscale engraving

0:12 now there are two forms of grayscale engraving

0:18 some people try to do grayscale engraving of photographs

0:24 i’ve seen some half reasonable representations of photographs but it’s a very difficult process very

0:32 edgy process that’s balanced on the head of a pin no it’s balanced on the point of a pin

0:41 it takes very little to make it fall off there’s a very good reason for the instability of that process

0:47 now i haven’t touched grayscale engraving for probably two maybe three years now so we’re going

0:55 to start off by a quick reprise on what i already know

1:00 and the problems that i know that we’re going to encounter because let’s take the first type of

1:08grayscale engraving which is call it photo engraving because there is no other reason why

1:15you’d want to do grayscale other than to emulate photographs

1:21well here we are in photoshop again looking at this lovely lady that was successfully managed to barbecue

1:26and mel treat should i say over the past couple of sessions

1:33we might be doing the same thing today but she’s a very good example of what i want to show you now we’ve got

1:40a colored picture here which we know we can’t work with and so the first thing we have to do with this picture is to remove the color

1:47before the days of digital photography that would have been a continuous

1:53graduation of anything from white to black on that image i know it looks as though

2:00it’s a continuous change from white to black but that’s because your eyes cannot see the detail

Transcript for Grayscale Laser Engraving (Cont…)

2:06that’s actually in that picture as i demonstrated to you on previous occasions your eye is very good at fooling you

2:13and your brain builds up a picture which is not a real picture so here we are there’s the corner of her

2:19pupil now you can see the little pixels in there all the

2:25various shades of black to almost white now digital graphics has its own rules

2:32and one of the simple rules about grayscale is we have 256 shades of gray

2:39now that’s not quite true because we actually have 254

2:44shades of gray but there are two special colors one

2:51at color zero which is black and the other which is color two five

2:57five which is white so we’ve got black and white and 254

3:04shades of black white mixing in between and when you mix black and white you get

3:10gray and when we get in between at around about 125 we get mid gray half black half white

3:18so that’s the way that grayscale actually operates in the digital medium

3:23the thing about the rawweda controller and several other digital controllers as well

3:28is the keyword digital it has the ability to analyze this picture and understand

3:36what each of these shades of gray is and you can apportion a

3:43power to every one of those shades of gray so we could instead of going across this

3:50picture here and going black white black white black black black black white black black white

3:55as we do with dot divided graphics we could go white white white dark gray

Transcript for Grayscale Laser Engraving (Cont…)

4:02dark gray pale gray pale gray dark gray mid gray and every pixel that we come across

4:10instead of just putting a little dot of power down we could change the power level

4:15and we instead of putting dots down what we’re doing we’re burning continuously but we’re burning with different levels

4:22of power a different power for every pixel now let’s just consider that for a moment

4:28how staggering that actually is now a grayscale image and a dithered image are different

4:35in the way in which the machines normally approach them in the case of a divided image which is what we’ve got here as soon as we hit

4:42a pixel the power turns on and as soon as we hit white between the pixels the power turns off

4:47so it’s on off on off and then we get a set of black pixels which are all joined together

4:52and the power turns on and stays on for the whole duration of that line that joint there is no

4:58individual pixels as far as the machine is concerned when it comes to grayscale we have a different situation

5:05here we’ve got four pixels that i just happen to have drawn like this and i’ve colored them to show that each

5:10one has got a different grayscale level okay so we come across the first pixel

5:18and we don’t switch on because the power is already switched on we switch on to a specific power

5:25and we burn the first pixel then we move on to the second pixel which is a completely different power

5:31and we burn that so we continuously changing power for every

5:37single pixel let’s just have a quick look at the numbers if we happen to make our

5:44image 254 pixels per inch that equates to a pixel being 0.1

5:51millimeters wide now what sort of speed are we going

5:57to engrave at i’d like to engrave a thousand millimeters a second but i’ve not been able to achieve that yet

6:04so let’s just stay reasonable and say 500 millimeters a second if we’re doing 500 millimeters in one

6:11second it means that in two milliseconds we’re going to cover a millimeter we’ve

6:17got pixels that are 0.1 millimeters wide so we’ve got 10 pixels in every millimeter

6:26so what that means is the time per pixel is actually 0.2 milliseconds

6:32or 200 microseconds i mean they’re really unimaginably small

6:38periods of time as far as our brain is concerned in electronic times it’s not

6:44particularly fast and we’ve already seen from our previous work that 200 microsecond pulses

6:51are a doddle for this machine so we have no problem at all with response speed we should be able to

6:57jump between the power at 500 millimeters a second now wood or paper

7:05or card or leather can only do two things

7:14not burn which is white or burn in some way which gives us a

7:21color now if we burn it hard enough we get a dark color which could be close to

7:28black but unless we get rid of all of the organic material

7:33and leave carbon behind we will not get black if we get black we’re going to

7:40finish up with a barbecue so we know that we’re unable to get black

7:45on an organic material the best that we’re going to get is some sort of dark brown

7:52so our color range is going to be limited to what we see here a sepia

7:59look we’ve got to somehow work with 256 shades of

Transcript for Grayscale Laser Engraving (Cont…)

8:04a much more limited palette of brown now scorching is a very difficult

8:11problem to do i know it’s very easy to scorch but

8:16when you’re trying to do controlled scorching it’s not as simple as you think when we drive a glass tube we get an

8:24output from the controller which is anything between 0 and 100 and what that’s really doing

8:32that is controlling

8:38milliamps and it does it in a completely linear fashion fifty percent power it was fifty percent

8:45of the milliamps that can be delivered by the power supply what happens is the power

8:51because of the physics does not come out in a linear manner it often comes out

8:56like this so we get a non-linear relationship between zero and a hundred percent

9:03power so it looks as though fifty percent power is probably closer to something like about 50 watts

9:11not 30 watts as you may expect so when we look at this a little bit closer we find that we’ve got

9:1760 watts here equal to our black zero watts here equal to our white

9:24and as we’ve just said when we want mid gray we want fifty percent white and fifty percent black

9:30so you would think hang on fifty percent power is mid-gray well look you can see that

9:37it’s not mid-gray because we’ve got this non-linear characteristic between our max and our min power so

9:46that’s problem number one we’re going to get a distortion of our color range we can distort this

9:52power curve to make this a linear output there are ways of doing that in photoshop

9:58which i’m not going to go into now because it’s not important at this point in time but let’s just assume for a minute and

Transcript for Grayscale Laser Engraving (Cont…)

10:04i’m going to draw as a dotted line that we have got the ideal characteristic that runs up there

10:10now the great thing about this constant power output machine is

10:16when we ask for 50 power we get 30 watts that isn’t the same

10:23with the rf machine okay so there’s a pwm signal

10:29which basically runs between zero and roughly five volts that’s the signal that’s sent to the

10:36actual tube itself and that’s a switch on signal

10:41for the tube we don’t control the power of the tube what we do is control the switching

10:49that’s all we do the power of the tube is what it is if it’s a 30 watt tube then

10:55when we switch it on we shall get 30 watts

11:01when we switch it off we get zero watts 30 watts zero watts 30 watts

11:09zero watts so the electrical engineers amongst you will say well on average that means that

11:16we’ve got 15 watts being delivered through there wrong

11:24we’re not interested in average because the material doesn’t see average

11:30power what it sees it sees 30 watts for 50 percent of the time so the material

11:37doesn’t know anything about maths and averaging all it will do is see that it’s being

11:43hit with 30 watts 50 of the time so we do not have the opportunity to control the power of this

11:49rf tube in the same way that we can control the power on a glass tube if we want fifty percent

11:56power on a glass tube we get fifty percent power

Transcript for Grayscale Laser Engraving (Cont…)

12:01if we want fifty percent power on here we can’t get it we can get full power for fifty percent

12:08of the time but that’s not the same thing if we change

12:13the parameters to say one percent equals white

12:20and 199 percent equals black

12:26what do we get well we get 30 watts still on

12:33for one percent of the time we still get 30 watts but the question

12:40is if that was a candle as we’ve used this example many times before

12:46and i put my hand over there for 100 of the time it would burn if i put my hand over

12:52there for one percent of the time how much damage am i going to do not

12:58much so maybe if we look at it in this way

13:03white could be a light scorch

13:10and 99 percent of the time could be

13:18black we’re still going to get 30 watts per

13:24pulse but 30 watts for a very short period of time is not going to be able to damage the

13:32material because we’re not holding the power on long enough to damage the material and the candle

13:38flame is the best example i can give you of that

13:44so that’s the second problem maybe we’re going to be okay

13:51now here’s the third problem material they’ve already started to speak about

13:56this here we go look we’ve got basically what i call grainless wood here then of

Transcript for Grayscale Laser Engraving (Cont…)

14:04course we’ve got the real thing here wood and now and then we’ve got other

14:10materials like this which is anodized aluminium glass

14:16you can probably just see on there some marking on that glass it’s white the marking on here is white

14:24here we’ve got some slate the marking on there is gray well we can’t use grayscale

14:31to produce a photo on there because we’ve only got one

14:37color that we can work with so material we can

14:43engrave possibly on organic material we definitely cannot do anything with

14:49non-organic materials now this image looks as though it’s got different

14:54shades of brown in it wrong it has only got one shade of brown

15:01in it because we used the same power for every single dot on this image

15:06your eye is fooling you again there’s only one color in there and that’s brown the other

15:14color is white and your eye is mixing the relationship between those two and the density of the dots the

15:21closeness of the dots is making the apparent different shade of brown

15:27so the next problem that we’re going to encounter is how do we produce different shades of brown on an organic

15:32material more power i can hear that’s what you’re saying yeah yeah just put more power in the more power we put in the darker

15:38image we get okay so our first challenge is to get black

15:44okay so that’s a nice pattern to see what color we get it looks very light because hey there’s

15:51white wood between it the reason i’m running it at 500 millimeters a second is because if you like that’s what we

15:58did the calculations for that’s 500 millimeters a second 100 percent power with our 35 watts that we’re

Transcript for Grayscale Laser Engraving (Cont…)

16:04throwing at the job and we’re using a two and a half inch lens i think i’m using a fairly what i class as soft

16:12lens it hasn’t got a really really sharp point on it it doesn’t dig in a great deal now if we’ve got point

16:18five pitch between the lines and we’ve got a gap that’s 0.2 it means the lines are 0.3 wide just to

16:25confirm it there’s my 0.5 pitch how do we make it darker we’re already running at 100

16:31power we’ve thrown the maximum amount of power at it we’ve got a soft lens which means we’re not doing

16:38too much heavy burning if you take a look down the middle here we’ve got just uh the nearest brown line

16:46down the middle where we’ve got the maximum power at the point of the beam doing a little bit more damage if we

16:52want to do more damage we have to move slower so let’s drop the speed down to 400

17:00there’s one way to get color into the job let’s have a look at those under the microscope there’s the 500 millimeters a

17:06second and there’s 400 millimeters a second as you can see we’re getting a little bit more color in

17:12and we’re getting more effect in the bottom we’re having the sharp

17:17point having a bit more effect as you can see now we drop down to 300 you can see now

17:23the central high energy part of the beam doing the damage in the bottom of the groove we’ve gone

17:30down from 500 to 300 and we haven’t significantly changed the

17:35line thickness it’s gone up a little bit to 200

17:41we’ve got a lot more color now in the whole of the beam we’ve still got

17:47the central core running through but we’ve got more color on the side

17:52wall of the beam we’re getting deeper with the v now we drop down to 100

17:59we’re now producing some serious damage we’re burning along the edge now but we’ve got a very very deep

Transcript for Grayscale Laser Engraving (Cont…)

18:06groove down here and now we drop down from 100 to 50 we’ve got burning on the surface

18:13and yet we haven’t got burning down in the depth of the groove itself

18:23without too much effort look i’m able to peel away or that black we’ve still got some color

18:31in the bottom of our grooves even though i’ve peeled it most of it away but we are

18:37what a millimeter deep that’s not what we want we want to scorch the surface we don’t want to cut

18:43through to the other side of our material so if speed is not the answer to our question

18:49five millimeters nominal focus 500 millimeters a second

18:57and there’s our starting position

19:02so the other alternative we’ve got is to make the beam even softer and we can make the beam

19:09even softer by changing the focus to six millimeters

19:14no change to the program

19:20well there we are at five millimeters focus

19:26six millimeter focus seven millimeter focus

19:33eight millimeter nine millimeter but the only thing you can say is look at the line thickness

19:39the line thickness is going up but the color isn’t changing so if we take that worst case focus

19:45which is a point almost a 0.5 wide line and i try and change the

19:50speed for that one now well there’s our 10 millimeter out of focus

19:56at 500 millimeters a second 400 millimeters a second 300 millimeters

Transcript for Grayscale Laser Engraving (Cont…)

20:03a second and 200 millimeters a second so yes we’re making some color change now but

20:09again we’re slowing it down we’re making the burn last longer but the problem is making the burn last

20:16longer is changing the color but look if we catch this in the light right you can see

20:22that we’ve got quite a lot of depth to the cuts so changing the focus and the speed

20:29is not a solution so let’s close the picture to make the lines touch at 0.25

20:38now when you look at that you think to yourself wow look at those scorch lines right down

20:43the center of the cut but when i show you what the end looks

20:48like you’ll be rather surprised they’re not the scorch lines down the center of the

20:54cut those are the scorches on the surface of the material the cut is lovely and clean we take a

21:01look at that one there 500 millimeters a second

21:09but a 10 millimeter gap in other words it was well out of focus look at the difference in color between

21:17the raw material around the outside and the excavated material wouldn’t you expect

21:24something that is half a millimeter deep to be burnt how do i get half a millimeter

21:31deep excavation without any color hardly this is one of the other problems you

21:37have when you’re messing around with wood or organic materials you have to

21:42understand the material properties themselves it isn’t just a matter of throwing power

21:47at this job and creating toast we don’t want burnt toast what we really

21:54want is a well scorched surface we need to just quickly break off for a minute and talk about

Transcript for Grayscale Laser Engraving (Cont…)

22:02materials because hey unless you understand how materials burn

22:10in this case organic materials you won’t understand

22:15what you’re seeing between that and that okay out comes my plumbing kit

22:22again laser beam [Music]

22:29lots of energy down the center of the beam and not much around the outside

22:34we’ve already established that we’ve got the distribution of that curve like that the gaussian distribution of energy

22:41intensity the light intensity across the laser beam itself we put it through a lens doesn’t matter

22:48which way the lens is let’s put the lens that way because that’s the most common way to do it and we turn the beam into a

22:56focused beam and at that point there we’ve got a little footprint where we’ve

23:03focused all the energy down into one very small spot okay now the energy that we’re focusing

23:09down into that spot is light energy it’s not heat it’s just pure light

23:17and if we like to compare what’s happening there with what’s happening here it’s a little

23:24micro picture of the same thing so when we look at the burn area

23:30which is this area here we shall find that it has still got this gaussian distribution of light and in

23:36fact it gets amplified even more to something that looks like that where

23:42we’ve got very very high energy distribution at the center that means that we’re

23:48going to do maximum amount of damage right in the center of this little spot

23:54that we’re burning into the surface and as i said we’ve seen that on the pictures where i’ve pointed out to you

23:59the line down the center of the groove where we’ve got this high energy part of

Transcript for Grayscale Laser Engraving (Cont…)

24:04the beam doing most damage as i said this is light it is not heat

24:12and i’ve tried to describe to you in a few other sessions the way that the energy transfer takes

24:18place is by the molecules in the wood or any material but in this case wood

24:25being vibrated they’re naturally doing this and vibrating at room temperature okay

24:33now i say room temperature because this is a measure of what room temperature is

24:39if i do that i’ve gone above room temperature faster a molecule vibrates the higher its temperature when you

24:46stimulate a molecule with the right frequency of light gets excited and goes

24:51much faster in its vibration level and as it gets faster and faster it gets hotter and hotter if it was

24:57water and we’ve heated it up to 100 degrees c the water molecules they would evaporate

25:05and turn into steam this isn’t water this is something else

25:10this is a chemical there are several different molecules in here one of them will be

25:16cellulose and that probably when it gets up to maybe 150

25:21200 degrees c it starts to scorch and turn brown

25:28get it up to maybe 280 300 degrees c and it starts to evaporate and turn into

25:35smoke that’s a chemical change that’s taking place in the cellulose the cellulose structure is now breaking down

25:41because of the heat it’s going so fast it’s basically shaking itself to pieces and what it’s doing the pieces that are

25:48breaking off are combining with oxygen in the air and you’re getting an oxidation process

25:54so there’s all sorts of strange chemical reactions taking place within the molecule itself

Transcript for Grayscale Laser Engraving (Cont…)

26:01and it’s no longer the same molecule it’s changing to something else and it changes into smoke but there’s

26:07still lots of bits and pieces of the wood left the the cell wall of the

26:12cellulose is a material called lignin and that is a much harder material

26:20to break down and so that carries on vibrating until it gets maybe to 350 400

26:26degrees c where that disappears as well and what we’re left with then carbon now carbon

26:34sucks in the light energy from our beam and it really goes bonkers

26:44and as it goes bonkers [Applause] it starts to heat up dramatically there

26:49are various temperatures along the way that will happen and it depends whether or not the

26:54surface of the wood can get exposure to oxygen or not as to what happens to the carbon that’s

27:01in the surface as the carbon heats up it may well turn some of it into carbon monoxide

27:06some of it into carbon dioxide if you suppress oxygen away from the surface the carbon

27:12itself will get up to about over 3000 degrees c it’ll do something that chemists call

27:18sublimate it changes directly from solid to gas so those are the the three main

27:24stages of destruction of a organic material

27:30i’m going to fire the 30 odd watts of just raw beam at this piece of wood

27:36we’re doing it in this low energy mode before it gets focused through a lens because it’s much

27:42easier to see the mechanism of wood burning under these conditions i’m going to give it a little pulse

27:51and then another little pulse and i think that’s as much as i should

27:58do now it’s going to be very very difficult for you

Transcript for Grayscale Laser Engraving (Cont…)

28:03to try and understand what’s going on in that picture there because there is no 3dness and we can’t

28:10look at it from different angles but i have examined this little teeny weeny

28:16pit let’s call it and it’s about one millimeter deep in the center here

28:21here we’ve got the surface of the material around the outside and you can see the low intensity light area of the beam

28:29having an effect around the outside here this light scorching okay now this is where the

28:35molecules have got excited and they’ve sort of turned into scorch

28:41and then we’ve got these white structures here now these white structures here are

28:48very sensitive parts of the material they’ve eroded or been sensitized by the

28:55light a lot faster than these other sections because these are like crevasses they’re like fishes

29:03in the wood so the light has gone almost straight in and produced these

29:09fishes let’s just ignore those for the moment because it does show you how absolutely dramatically different wood

29:17is within just a few parts of a millimeter the molecular structure of the material

29:22responds differently to exactly the same light light scorching then we’ve got slightly heavier burning

29:29taking place around here and we’re beginning to see as the energy increases and the pit starts to disappear inwards

29:37because that’s what’s happening here we’re going from nothing gradually inwards into a slightly saucer shaped

29:45center here and what we’ve got here are granules of carbon

29:54and then we gradually worked our way and eroded our way or evaporated the carbon away

Transcript for Grayscale Laser Engraving (Cont…)

30:00and got back to clean wood in the center here light cannot penetrate the wood light can only

30:07affect what it sees on the surface if it sees cellulose

30:12the cellulose is the thing that will react to the light when the cellulose disappears the lignan gets exposed to the light and

30:20that reacts accordingly and when the lignin disappears we get carbon and carbon sucks in the energy

30:26very quickly and disappears and here it is look it’s gone black and now it’s disappeared and

30:32in the center there we’ve got raw wood again ready to accept a new attack from the light what we’re

30:39really looking for is a very soft burn

30:44that will give us control over the difference between a scorch before

30:51we go through the carbon phase so everything needs to be on the surface

30:59now we’ve already tried that with two inch with a two and a half inch lens which is

31:05a pretty soft lens in most people’s books but i’m very

31:10lucky that i have the support of cloud ray you would never think of using anything like this

31:15on any of these machines let alone with a 30 watt machine what we’ve got here is a 190.5

31:25millimeter focal length lens my lens as you can see the lens in the top here

31:31190.5 is about here so let me raise the table a little let’s

31:36say we’re not far off there just do a quick pulse to see what size the beam is

31:43and that is i would guess it’s probably a millimeter diameter try something

31:49to start with we’ll go for one millimeter line spacings 190.5

31:58 divide that by 25.4 because yeah it’s a seven and a half inch lens

Transcript for Grayscale Laser Engraving (Cont…)

32:04 but it was going to be one millimeter wide beam but in fact it looks as though it’s around about 0.6

32:12 maybe 0.7 so to get that beam to close up we’ll start off by closing the beam up

32:18 to 0.6

32:25 and hey look we’ve made it just a little bit darker point three got a little bit more color into it now

32:32 and point one so we’re getting definitely more color into it the problem is not only have we got more

32:37 color into it now we’ve got we’ve got something that is

32:44 a lovely smooth cut but it’s about three quarters of a mil nearly nearly a

32:50 millimeter day not really winning we’re proving that if we can overlap we

32:56 can get multiple burns but hey look we’re getting multiple burns without producing any carbon

33:03 so we must be quickly going through that carbon phase and finishing up with wood again

33:11 just a slightly brown wood so let me see if i can reduce the power

33:17 change the depth and change the color or change the power now to 50 percent

33:24 it’s still way out of focus

33:34 absolutely no difference to the color even with this very very very soft pencil if you like

33:41 it it’s a very very very blunt pencil one millimeter diameter and going over it ten times because

33:47 we’ve got roughly a a one millimeter beam and we’re scanning over this at 0.1

33:53 so we’re running over every burn roughly 10 times and we still can’t make

Transcript for Grayscale Laser Engraving (Cont…)

34:00 a serious color we can’t get close to black

34:06 i had an interesting thought am i tackling this problem the wrong way because hey one of the things if you remember

34:12 what i’ve just done [Applause] we’ve got a seven and a half inch lens

34:18 sitting up here way down here we’ve got our work

34:26 so that’s already focusing the beam down

34:36 now what i’m going to try now is the completely opposite approach

34:43 i’m going to put my compound lens in here

34:50 i’ll just draw it like this okay because normally that compound lens

34:58 has got a focal distance of around about 21 millimeters something like that

35:05 okay and it goes out of focus quite quickly

35:11 so if i can get it to go out of focus quite quickly then i’m hoping that

35:17 it will actually create the soft burn that i want but

35:25 the problem is it goes out of focus very very quickly so what i’m actually going to try is

35:32 something a bit different we’ll try the focal we’ll try that lens on its own afterwards

35:38 but first of all what i’m hoping i’ll be able to do is to grab hold of this beam here

35:44 like this and make sure that i get my

35:49 [Applause]

35:57 now what i’m trying to do is that i’m trying to get it to go out of focus quickly but not grow in diameter let’s give it a try

Transcript for Grayscale Laser Engraving (Cont…)

36:04 and see what we get a completely back to front approach to this problem i hope this confirms for

36:09 you that none of this stuff is pre-ordained i’m not trying to teach you anything i’m trying to so here we

36:15 are with a 7.5 inch lens here and a compound lens sitting down here

36:21 you see normally this would be set at 11 millimeters why don’t i set it to start with to 11

36:27 millimeters and see what we get we’re running at 700 millimeters a second we’ve got a distance we’ve got a

36:33 scanning interval of 0.1 and we’re running 100 power

36:45 and we’ve got some depth not a very dark color 25 35

36:52 45

37:05 it wasn’t my intention but this has been a classic demonstration of what i described to you

37:11 about the way in which wood burns in layers

37:17 here we start off with we’re so far out of focus that all we’ve done we’ve had enough energy there

37:24 to just scorch the surface very lightly as we increase the energy density in the

37:31 beam we’re gradually putting more and more

37:36 color we haven’t yet burned through the layer here

37:44 we’re still producing carbon that’s on the surface you can see that we just rubbed a very

37:50 small amount off and now probably here we’re starting to get some

37:55 loose carbon no there’s not much of it

Transcript for Grayscale Laser Engraving (Cont…)

38:02 here i can feel us here we go look we’ve got a little smudge of carbon coming off

38:08 loose now this one a lot more

38:14 and we’ve got some depth in that one and this one and this one

38:21 and now look we’re getting lighter so we’ve reached our peak here at around

38:28 about 27 so we’ve gone from scorch to

38:34 a carbon layer and now we’re gradually working our way through the carbon layer

38:40 it’s evaporating off here and we’re actually getting lighter and

38:45 we’re working our way through into clean wood again

38:52 as we increase the energy density we’re actually cutting deeper but we’re

38:59 cutting through this layer effect that i was describing to

39:05 you okay let’s give this little program a try

39:11 well there should be six different grades one two three four five six

39:18 so there’s two missing so let me try something else one to a hundred

39:31 25 to 100.

39:39 so these are the percentage powers that i’m using for this now there should be one two three four

39:46 five and this one on the end here should be what it is white

39:54 no matter how hard i try i’m struggling with the fundamental problem of getting

Transcript for Grayscale Laser Engraving (Cont…)

40:00 color into the material and this takes us full circle to where

40:05 we started off from my concern that we wouldn’t be able to do this

40:12 i mean at the moment we’ve got point four line thicknesses

40:18 that’s not going to reduce a very high resolution picture in grayscale now just in case that material moves

40:27 i’ve held it down with magnets so the settings we want are these 25 and 100

40:34 well let’s give it a try well i did warn you that we were likely

40:40 to do this young lady some fairly serious injustices today and yeah i think we’ve succeeded in

40:49 seeing it in a sombre mood now i think what we really conclude from

40:56 here is that as i pessimistically started out saying

41:03 i don’t think this machine is suitable for grayscale photo engraving

41:10 i don’t think any machine is really suitable for for grayscale photo engraving there will

41:16 be people that can do it to some extent remember i said at the beginning it’s a process

41:22 that’s balanced on the point of a pin and i think by looking at the various elements that i’ve spoken of today you can see

41:28 just how precarious this process is it’s not a durable process so if you are successful at doing it

41:36 congratulations because your parameters will be great for your machine with your lens under

41:41 your conditions that’s another negative as far as i’m concerned so we mustn’t blame that on

41:46 this machine i’m trying to remain positive you see this machine

41:52 should be able to do the other sort of grayscale engraving though which is 3d engraving which we will

41:59 tackle next time in a very unexpected way we’ve done some prototype work today

Transcript for Grayscale Laser Engraving (Cont…)

42:05 with our little swatches for 3d engraving now with 3d engraving the last thing we

42:11 want is black mucky engraving now i’ve seen some of the stuff that’s done by the big

42:18 professional guys and they basically scorch off the material to start with and then they’re

42:25 going to go with a couple of finishing cuts to clean the job up that seems to be totally the wrong approach

42:31 don’t scorch it at all if you get the cut right as you’ve seen here look i’ve got a cut

42:37 that’s a millimeter deep and it’s not scorched it’s just a nice shade of brown

42:44 that’s what we want we want cuts deep without charcoal and as i hope you

42:50 absorbed today and now believe me when i say that there is a process by which you can go through from

42:58 light to carbon and back to light again okay we’re burning in layers

43:04 now today is a classic example of what these sessions are all about this is me learning i’m not i’m not

43:12 worried whether you have the patience to sit through and watch this because this is nothing to do with you unless

43:18 you really are interested in what i’m doing the outcome you might be interested in

43:24 the process probably not too many of you are interested in the process but those of you that managed to stick through to

43:30 the end thank you very much for your time and patience and i shall see you in the next session