Hi Guys,

Thanks to suggestions from others I have been able to improve my technique and this is the latest Lithophane, laser cut into Corian.
As there is no Z axis movement I was able to use a constant velocity of 4000mm / min for the X axis (excepting the acceleration and deceleration zones for each line scan). The final work does need backlighting (unlike opal Plexiglas) so it looks like I will be making a few of John’s (PicEngraver) LED / diffuser light frames when I get a chance. 

Tweakie.

Very nice Tweakie, do you have a link to Johns frames? Not sure I saw those.

Dave

Dave,
PDF here: http://www.picengrave.com/downloads/Lithophane%20Light%20Panels.pdf
Regards,
John Champlain
www.picengrave.com

Thanks, John, I see I set mine up "almost" like yours (http://www.machsupport.com/forum/index.php/topic,22972.0.html ), but I see you added the light diffuser as well.

I bet that would even out the light a bit more across the back of the image for sure. Nice touch, and I will have to add that to my toolbag for future use.

Thanks for sharing-
Dave

Thanks John, I have been searching for that link for ages 

Tweakie.

At the risk of rambling on a bit, I have been closely following the absolutely excellent and quite pioneering work which is being done with low power diode lasers by John, Jeff, Dave and others in different parts of the world - for those that may be interested these threads relate;

http://www.machsupport.com/forum/index.php/topic,23456.0.html
http://www.machsupport.com/forum/index.php/topic,23584.0.html

Whilst I am quite certain that it can be done, replicating their work using a CO2 laser is not without it’s difficulties (cracking a nut with a lump hammer comes to mind) but, hopefully, I will get there.  

Tweakie.

A picture of a very good friend, laser etched using GCode produced with the free software DotG.

Tweakie.

Hi Tweakie,

I am newbie for laser engraving, I just completed my cnc router recently and am immediately interested in the laser engraving after reading some of your posts. You guys are genius!!!

I have a couple question about dotG & your post processor,
1. How does it control the 'on time'(duration of laser on) of the laser? Is it achieved by changing the Z axis feed rate while X axis is in constant feed rate for each 'dot'?
2. Is it sharing the same idea as Art's impact/engraving plugin? So dotG is basically outputting a TTL signal to trigger the laser?
3. Could you paste several lines of GCode to help me understand how it works? Unfortunately I am not able to install dotG at the moment, it gives me 'cannot create file' error, will sort it out later.

Thanks so much.

Yanxin

Hi Yanxin,

DotG has been designed for reproducing a one bit, ‘dot-dithered’ image (one with a varying density of equal sized dots to create the illusion of shade) and when set in ‘dot’ mode the laser is only fired when the X and Y axes are stationary.

To fire the laser I am using the M11P1/M10P1 command set together with an imaginary B axis and my Post Processor (see posting #641) essentially creates this code for each dot in the image:-

B0

M11P1 B1
M10P1 B0

B0 is at the start of the code and makes sure the imaginary B axis is in position 0.

M11P1 turns on Output #1 (as soon as the B axis starts to move). Output #1 is mapped to an LPT (parallel port) output pin which is in turn connected to my laser TTL(L) trigger.
Because the imaginary B axis takes time to move from position 0 to position 1, I have adjusted (by trial and error) the steps per unit, Velocity and Acceleration of this axis to produce the required time delay (laser on time).

M10P1 turns off Output #1 and thus the laser trigger as soon as the B axis starts to move back to position 0.

I hope this answers your questions.

Tweakie.

Thank you for the detailed explanation, Tweakie, I understand how dotG works now, it's like a real PWM. If I understand correctly, the impact/engraving plugin is doing "fixed time" pulsing(60us?) with variable reasonable repetition rate.

Hope I can show off my first art piece one day:) Still a long way to go. Thanks again!

Yanxin

Hi Yanxin,

I am looking forward to seeing some pictures of your work.

(You are quite correct about the Impact / Laser plugin - it uses a fixed time interval (PWM) of 40uS and a variable repetition frequency (PRF) of between 0 and 12.5 kHz and, of course, fires the laser whilst the axis is moving).

Tweakie.