20 – 3D Laser Engraving With Grayscale

The Tangerine Tiger Series with Russ Sadler

In this Series, Russ has purchased a new 500 x 300mm, 50W laser machine from eBay with a view to modifying and upgrading it. In fact, he rips out the glass laser tube and high voltage power supply and replaces them with an RF laser source and PSU from Cloudray. Find out how the expensive RF laser source compares to a glass CO2 laser tube and prepare to get your hands dirty! So read on to learn about 3D Laser Engraving with Grayscale.

3d laser engraving with grayscale
3D Laser Engraving With Grayscale

If you are considering purchasing a CO2 laser machine with an RF laser source from one of the big boy suppliers, I would suggest you check out this series before making a decision!

Contents

The RF Technology’s ability to almost instantly switch to different power levels, makes it well suited to creating a variable depth scan line. Add all these scan lines together and proper 3D engraving is the result. I have successfully mastered the process on my glass tube machine, but the PWM manner of tube control used by the RF technology appears to offer different challenges. I explained the process of “burning” wood with a laser beam in the previous session and showed that with well-chosen parameters it was possible to excavate a significant volume of wood and NOT leave a charred surface behind.

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Transcript for 3D Laser Engraving With Grayscale

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0:00 well thanks for joining me and my little

0:03 tangerine tiger here tonight um it’s a

0:06 bit cold in this workshop but

0:07 a the things i do for the love of

0:09 education

0:11 well i’m starting a little bit early

0:12 this year i’ve got my christmas mug out

0:14 trying to get a bit of christmas spirit

0:17 going i mean it’s been a funny old year

0:19 um whichever part of the world you’re in

0:22 i’m sure that you’ve been um

0:24 suffering a little bit whether it’s

0:26 through uh

0:28 a pandemic or whether it’s through

0:30 politics

0:31 um i’m sure we all suffer the same

0:33 problems so um

0:35 my heartfelt sympathies go out to all of

0:37 you last time

0:38 we tackled the what i call the flaky

0:40 part of grayscale engraving

0:44 you would think that grayscale engraving

0:48 and grayscale photographs would go

0:51 together

0:51 and make a perfect marriage i think we

0:54 demonstrated that

0:56 it was rather difficult and probably not

0:58 a very good

1:00 stable process today we’re going to

1:02 tackle the more credible part

1:03 of grayscale engraving and that is

1:07 3d engraving in the same way that

1:09 grayscale

1:10 photo engraving could only be done on

1:13 certain materials

1:14 there had to be materials that would

1:16 scorch grayscale

1:19 3d engraving can only be done on certain

1:22 materials

1:22 and it won’t be the same group of

1:24 materials for instance

1:26 we can’t 3d engrave a piece of card or

1:28 paper

1:29 it has to be a piece of wood with some

1:31 thickness on it for example

1:33 leather i’ve never tried to engrave

1:35 leather but i suppose it’s possible but

1:37 i’m sure it would be

1:38 very difficult to charcoal it by the

1:40 time you finished plastics

1:42 materials like corian for example which

1:44 are basically

1:46 a powder filled acrylic material you’ll

1:48 be able to

1:49 engrave acrylic all sorts of woods like

1:52 mdf

1:52 woolly grave plywood

1:56 ordinary wood many many ordinary woods

1:58 but

1:59 one of the problems with many ordinary

Transcript for 3D Laser Engraving With Grayscale (Cont…)

2:01 woods is the

2:02 huge change in the material texture

2:06 as you go within the wood itself because

2:09 you’ve got

2:09 resin you’ve got hard parts you’ve got

2:12 soft parts depending on the growth rings

2:14 that take place in the wood

2:15 the molecular makeup of the wood changes

2:18 and so consequently it’s very difficult

2:20 to get nice uniform

2:22 engraving with some woods now i’ve put

2:25 my little test pattern back into

2:26 photoshop

2:27 and i’ve converted it into a grayscale

2:29 image and then i’ve modified these first

2:32 five pixels here as you can see such

2:35 i’ve got black

2:36 three quarters black half black half

2:39 white which is mid gray

2:41 then we’ve got a quarter grey and

2:44 something that’s nearly white

2:46 so we’ve got a fairly reasonable quick

2:48 change over those first five pixels

2:50 but then when we look at the signals to

2:52 create the power

2:54 for these we should get an idea of

2:55 what’s going on

2:57 now i anticipate that for instance for

3:00 that pixel there it’ll be 100

3:02 on for this pixel here it’ll be roughly

3:04 50

3:05 on 50 off and this one here will be

3:07 nearly all off it’s not just a matter of

3:09 having this

3:10 grayscale on here we have to tell

3:13 rd works that we want to use grayscale

3:16 in other words we want to make

3:18 the signals for these colors

3:21 proportional to

3:22 the color and we do that by putting this

3:25 switch on here it’s called

3:26 output direct what we can do we can

3:29 choose here

3:30 min power and max power at the moment

3:33 i’ve got it set at one

3:34 for minimum power and a hundred percent

3:37 maximum power now what that means is

3:40 that i’m gonna use one percent to

3:43 represent white

3:44 two five five and 100

3:48 to represent 0 which is black so i’m

3:51 going to burn

3:52 as much as i can for black and as little

3:54 as i can for white

3:55 that’s fine until we look at the

3:56 calibration graph for this machine

4:00 now the tube itself is

Transcript for 3D Laser Engraving With Grayscale (Cont…)

4:04 it should technically be linear but in

4:07 reality

4:08 it doesn’t look as though the output is

4:09 linear it’s not bad

4:11 it’s it’s sort of linear but not

4:14 exactly if i was to choose 50 power here

4:18 i would get roughly 50 black and 50

4:21 white in other words i’d get a mid gray

4:23 it gets a little bit more complicated

4:25 than that

4:26 because below 10 we don’t mark the

4:28 material

4:29 so there isn’t any point in going down

4:31 below 10

4:33 so what we do we set that to 10 percent

4:36 and now what happens is this gradation

4:39 256 grades of black and white

4:43 are spread over 10 to 100

4:47 not over 1 to 100 so whatever range you

4:51 specify here

4:53 the grace go 250 divisions get divided

4:57 into the a scale that you set here the

4:59 max and min that gets subdivided into

5:01 256 parts

5:04 because of the pwm we have the choice of

5:07 a frequency of anything from 0 to 25

5:10 kilohertz

5:11 as a mechanical engineer i’m struggling

5:13 a little bit to try and work out

5:15 what the best combination is we’ll set

5:18 that to

5:20 20 kilohertz and we’ve got a speed

5:24 here of 100 millimeters a second

5:30 and there we go we’re expecting to see

5:33 if you remember

5:34 20 pulses per pixel

5:38 these are the first five pixels look

5:40 there’s a black one on permanently more

5:42 or less

5:42 this one is slightly lighter and it’s

5:46 off

5:46 for some of the time this one is mid

5:48 gray and it’s roughly 50

5:50 on 50 off this one is lighter

5:54 so it’s off more than it’s on and this

5:56 one is nearly white so it’s nearly off

5:58 most of the time and just a little bit

6:00 on

Transcript for 3D Laser Engraving With Grayscale (Cont…)

6:01 so if i change this frequency here to

6:03 say one

6:05 so that i get one pulse per pixel

6:08 and not not 20 pulses per pixel one

6:12 thousand

6:17 and there’s my first pixel there’s my

6:19 second pixel

6:21 there’s my third pixel my fourth and my

6:24 fifth pixel here are two things that are

6:26 exactly the same

6:27 relatively speaking they don’t look the

6:29 same but

6:31 i can either choose 20 kilohertz

6:35 and here are my pixels

6:39 we can see here the black one the dark

6:41 gray one

6:42 the 50 50 mid gray one then the lighter

6:45 gray one and the nearly white one

6:47 i mean the nearly white one is mainly

6:48 off and only just a little bit on and

6:51 here it’s 50

6:52 on 50 off but look i’ve got exactly the

6:56 same situation here

6:58 when i run instead of a 20 kilohertz

7:00 time base

7:01 if i run a one kilohertz time base i’ve

7:04 still got my power on

7:06 per pixel this is fifty percent power on

7:09 and fifty percent power off and this is

7:12 fifty percent power on

7:13 and fifty percent power off which of

7:15 them produces

7:17 the biggest burn let me try and put this

7:20 into some sort of humorous perspective

7:23 that helps me to try and analyze the

7:25 amount of damage

7:27 that would take place under these two

7:28 different circumstances

7:30 if i was intent on committing suicide i

7:33 could jump out of the ground floor

7:35 window

7:35 20 times or i could go to floor number

7:40 20

7:40 and jump out once now i know it’s a

7:43 fairly brutal

7:44 analogy but i’m going to do a lot more

7:45 damage when i jump out from the 20th

7:47 floor

7:48 than if i’m going to jump out 20 times

7:50 from the ground floor if i leave it set

7:52 at 20 kilohertz

7:53 then this will automatically adjust

7:55 itself to whatever size pixel and

7:57 whatever speed i’m running and it’ll put

7:58 an appropriate number of pulses

Transcript for 3D Laser Engraving With Grayscale (Cont…)

8:01 in to each pixel but it doesn’t mean to

8:03 say i’m getting the best

8:04 amount of power out of this machine into

8:07 every pixel

8:08 if i want to try and do the analysis

8:10 carefully as i’ve done

8:12 with my spreadsheet and calculate

8:15 what the optimum frequency is to get

8:19 one pulse per pixel as opposed to

8:23 20 pulses per pixel i think i’m going to

8:25 get a much more

8:26 efficient burn out of this machine

8:29 okay now i’ve devised a very simple test

8:32 we’ve got a mid gray test square 10

8:35 millimeter square

8:36 like this now i’ve got a four inch lens

8:38 in here because i know from

8:40 previous experience with 3d engraving

8:43 that you actually need a long focus lens

8:47 previously i’d used a two and a half

8:49 this time i’m going to try and use a

8:50 four inch lens so this first test

8:53 is the 20 kilohertz test

8:56 [Music]

9:03 wow there’s a lot of material being

9:05 removed there now we do the one

9:06 kilohertz test beside it

9:18 so we’ll just do a quick measurement

9:19 approximately a millimeter

9:24 no different color no different

9:28 finish no different so it appears i’m

9:31 worrying unnecessarily

9:33 they come out to the same result i had

9:36 the air assist on

9:37 so i was blowing the smoke back down

9:38 onto the job i’m going to turn the air

9:40 assist off now

9:42 and see what effect it has

9:48 okay so that’s good that’s hardly made a

9:51 mark on it at all look it’s

9:52 pretty clean so we’re not blowing the

9:54 crap down onto the job

9:56 so that’s the one kilohertz

10:00 as opposed to 20 kilohertz

Transcript for 3D Laser Engraving With Grayscale (Cont…)

10:04 let’s just try the 20 kilohertz beside

10:06 it this time

10:08 just to be sure that we’re comparing

10:11 eggs with eggs

10:13 now i look at that and i think to myself

10:14 i’ve got more damage along this bottom

10:16 edge here

10:18 with 20 kilohertz that i have

10:21 doing it the other way around i saw it

10:23 there and i thought

10:24 maybe that’s an exception but no it’s

10:26 repeated here as well so the one

10:28 kilohertz gives a cleaner engraving

10:30 result

10:30 we’re going to go and search on google

10:33 for

10:34 3 d

10:39 engraving

10:42 bitmaps and we get all these images to

10:45 look at so let’s just click on some of

10:47 these just click on the images

10:48 and these are special bitmaps you can’t

10:52 just

10:53 take any photograph and do an engraving

10:56 you have to have a special especially

10:59 prepared bitmap

11:01 because these bitmaps have got a strange

11:04 look to them they look almost like wax

11:06 this is a good example of what i mean

11:08 basically

11:10 if you could regard remember black is

11:13 zero and white is two five five

11:17 and there are all these levels of gray

11:19 in between those two numbers

11:21 so if you look at a survey map say a

11:23 mountain

11:25 there will be little rings around the

11:27 top of the mountain and

11:28 the size of the rings will tell you what

11:30 the shape of the mountain is as you go

11:31 further down the mountain

11:32 the rings will get bigger and they will

11:34 get all sorts of funny shapes but

11:36 the line that’s drawn that funny shape

11:39 is the height of the mountain it’s like

11:41 a slice

11:42 through the mountain well that’s

11:44 effectively what this is this is a 3d

11:46 object that has been sliced

11:48 this way and the lines that are on top

11:50 the layers that are on top

11:52 are white and the layers that at the

11:54 back are black

11:57 and that’s how we’ve got 3d nus into

11:59 this picture we’ve used the color

Transcript for 3D Laser Engraving With Grayscale (Cont…)

12:02 as a 3d feature

12:05 so you can’t just take an ordinary

12:07 photograph

12:08 and use it because it doesn’t have this

12:10 information in it

12:11 the color codes the third dimension

12:14 file import and there we go 100 no no no

12:17 no no

12:18 no we were running 100 millimeters a

12:21 second and taking big chunks out

12:23 i think we’ll run that around about 200

12:25 millimeters a second

12:26 i’m just guessing these parameters uh

12:30 advance it doesn’t make any difference

12:32 we’ll set it to 20 kilohertz

12:35 because we found that it makes no

12:36 difference and

12:39 minimum power here’s the difficult bit

12:42 because i don’t know at what level power

12:44 we shall see

12:46 nothing so i’m going to leave it set at

12:48 five

12:49 and a hundred we’ve got our output

12:50 direct switched on

12:54 and our swing um

12:57 i very much don’t we’re going to get

12:59 point one with a four inch lens it’s

13:01 probably going to be 0.2

13:04 so maybe

13:07 mind you if i do point one i should get

13:11 like a double cut

13:15 so yeah i think we’ll leave it at point

13:16 one the question is what should we

13:19 try and engrave if i engrave a piece of

13:22 plywood like this

13:24 then i’m going to get different layers

13:26 in it now that might be interesting

13:28 to see different layers in here

13:31 different colors

13:32 nice and grainless this popular plywood

13:34 this is very

13:35 soft so it should burn quite easily

13:41 i’m just putting the uh magnets on here

13:43 just to

13:44 just to hold it in place my focus should

13:46 be set to 15 but what i’m going to do

13:49 i’m going to set it to 14 so that is

13:54 probably going to go two or three

13:55 millimeters deep now this is a very long

13:57 focal length lens so it’s not going to

13:59 make a great deal of difference

14:00 to the focal distance if i change it by

Transcript for 3D Laser Engraving With Grayscale (Cont…)

14:03 a millimeter basically i’ve now set my

14:05 focus roughly one mil inside the

14:07 material this has got quite a big

14:09 program there’s a lot of information in

14:11 here

14:12 and i’ve probably mentioned to you

14:14 before what i do as soon as the pro

14:16 as soon as the head moves i’m going to

14:18 press pause

14:19 because the program is going to take

14:20 quite a long time to download

14:22 and i don’t like the machine to try and

14:23 walk and talk at the same time

14:25 okay so i’ve turned the air assist off

14:27 now because i don’t want air assist on

14:30 we’re just going to close the lid and

14:31 let the smoke get sucked away i just

14:33 remembered we did say that one

14:35 kilohertz was better because one

14:38 kilohertz actually

14:39 gave a cleaner result so we’re now going

14:42 to close the lid

14:43 getting a very very deep cut i think

14:46 it’s too brown

14:46 i think we should start again it’s

14:48 already doing a superb job

14:50 but i would like it to go faster not

14:52 quite such a deep cut we’ll change the

14:54 speed to

14:55 slightly less smoke because we’ll be

14:57 converting less

14:59 solid into gas so there’s our first pass

15:03 we’ve already got some quite nice

15:04 profile into it

15:06 and i’m just going to put a little mark

15:07 on here because that’s past number one

15:10 we have to do this multiple times you

15:13 could take a look in the middle here and

15:14 you’ll see there’s a little white

15:16 spot in the middle there where it hasn’t

15:19 cut

15:22 it’s the same as the outside here so

15:25 that has basically that’s the mountain

15:27 top

15:27 where we’ve got if you like no cutting

15:30 that’s five percent power which is not

15:34 having an effect at all

15:36 and this bit around the outside here is

15:38 100 power which is

15:40 digging away a lot deeper

15:43 so we just run the same program again

15:45 and again

15:46 and again to get deeper and deeper and

15:48 deeper because

15:49 whatever shape we’ve got there

15:51 proportionately the same percentage will

15:53 come off

15:54 every time so the more that came off

15:57 this time

15:58 the more will come off next time and so

16:00 the profile will gradually get more

Transcript for 3D Laser Engraving With Grayscale (Cont…)

16:02 3d as we take passes

16:07 okay we’re gonna run the fourth cut

16:10 and you can see it from the front

16:40 so there it is with all its information

16:44 looking at it front on you can’t really

16:46 see

16:47 how 3d is

16:52 when we look at it from the side

16:55 look at that using quite incredible the

16:59 definition

17:00 you’re getting on these features in the

17:02 middle here

17:10 well we did anticipate that this was

17:12 going to be one of the machines

17:13 strengths

17:14 because you only have to look at a

17:16 company called kerns

17:18 and they specialize in this sort of

17:19 stuff using rf lasers so

17:21 you know i knew that it was going to be

17:23 good but i have to say

17:25 that’s exceeded my expectations

17:29 took a little bit longer than i thought

17:30 but on the other hand it’s still not too

17:32 bad for 30 watts we found a way of

17:36 balancing the speed the material

17:39 extraction and the least amount of

17:42 damage

17:43 it’s a pale brown it’s not burned it’s

17:45 not barbecued

17:47 i’m very happy with the result and the

17:49 crispness and the the quality of it is

17:51 superb there isn’t even there’s no hint

17:54 of curtains on there at all

17:56 or those funny lines that i had

17:58 previously on my other machine

18:00 that only took about three and a half

Transcript for 3D Laser Engraving With Grayscale (Cont…)

18:01 minutes for a pass

18:03 and there was four of those so that’s

18:05 what 12 13 minutes

18:07 i suppose that’s not bad it’s nice to

18:09 find something really positive about

18:11 this machine even though it is rather

18:13 niche

18:14 well i think that basically concludes

18:16 our first very quick

18:17 preview if you like of what this

18:19 machine’s capabilities are

18:21 i think what we’re going to do now is

18:23 gradually go back to the beginning

18:25 start looking in much more detail at

18:28 things like photo engraving

18:30 and order engraving on different

18:33 materials

18:34 to see what the problems are and i

18:35 suspect that for that quality of work

18:38 on this price of machine kerns can’t get

18:41 anywhere near it

18:42 the only thing that limits us really is

18:44 30 watts

18:46 with 60 watts we’d ever been able to run

18:48 twice as fast we’d probably be able to

18:49 run it a thousand millimeters a second

18:51 thank you very much for your time and

18:52 patience again

18:53 and i hope this has been an interesting

18:55 session it certainly has been for me

18:58 and i’ll catch up with you next session

19:00 bye now

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