n00b: RDCAM - PPI, 3d engrave, tickle

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n00b: RDCAM - PPI, 3d engrave, tickle

Postby jcsbanks » Mon Mar 05, 2012 1:47 pm

Nice forum. I wanted to build a machine (physician, but electronics hobbyist and then just completed a part time 2 year project for Cobb tuning reverse engineering Nissan GTR) but didn't have the time. So I bought a Shenhui 1200x800mm with 100W RECI tube, directly imported on advice from the guys on Sawmillcreek engravers forum. Converted a stable to a workshop (which igull has visited and we have visited and admired his very nice self build controlled by Arduino, Lasersaur and Mac). Intention is for my wife to start her own laser cutting and engraving business with me as the tech support. We're getting very nice results indeed so far.

Machine uses RDCAM v5 which I really like, and after a month I have only discovered a few annoying bugs like the undo is over enthuisastic, at high resolution display you have to move the color bar to see everything properly, cut order display doesn't show optimizations when you first load, collapsing many layers into one still shows the old ones unless you save and reload. However, it is lean, fast, didn't choke on a ridiculous test of a 144Mpixel file I threw at it, and I have been making good progress looking at the .ai and .bmp imports from CorelDraw with the aim of writing a printer driver (so far tested Abode generic postscript driver to print to a file and then using Ghostscript to convert to .ai and it is promising).

Three interesting features of RDCAM v5 I've been playing with and am about to that I will throw in for discussion and input.

1. There is a "dot" mode instead of "cut" where you can effectively set PPI. I have been reading the threads on here and will try some more settings.

2. It can "3d" engrave (referred to in one line vaguely in the manual as output direct) where the PWM signal to control the laser current varies from "min power" at white (RGB 0xffffff) and "max power" at black (RGB 0x000000) and interpolates on the fly. It produces a true undithered engrave and I had good results with a bidirectional engrave at min power of 0 and max power of 30% on my 100W tube, at 1 or 2 passes at 100-200mm/s. The machine will engrave at 400mm/s when you use the traditional on/off bitbang method, but it needs to be slowed down to get the definition for 3d engrave. For commercial products at this power I think it is a little slow, but I may use it more. Power was limited to 30% at the slower speed to get response time and avoid excessive charring, but I will revisit with upgraded compressor.

3. Using the output direct I'm considering adding 5% grayscale tickle pulses to my image to see if it improves response time and removes a "splatter" I get at more than 30% power at 800mm/s (but not at slower speeds) where the laser when it turns off does as it should and then about a millimetre later can fire again.

I know a 100W Chinese tube, even the supposedly better RECI is a bit of a blunt instrument for very fast and detailed engraving, but I push everything (except the tube current) to its limits to test and optimise.

In terms of cutting, I can do 18.7mm pine at 90% power at 3mm/s. 3mm laser ply cuts at 100mm/s. Most of our work will be artistic cutting I thought, but initial commercial interest before we've tried any marketing, just by word of mouth, is for engraving. If I improve responsiveness of the laser at 800mm/s for higher power, then I might consider x-axis motion control upgrade to servo as the mainboard is supposed to be able to do 1500mm/s.

From reading the threads on here I thought this would be interesting to you guys and you might have some useful thoughts for me on the topics.
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Joined: Mon Mar 05, 2012 1:11 pm

Re: n00b: RDCAM - PPI, 3d engrave, tickle

Postby jcsbanks » Mon Mar 05, 2012 11:32 pm

Tickle idea isn't going to work I think. When in output direct (3d) mode where it uses grayscale to set power, it doesn't seem to bitbang the TTL line but appears to leave it on whilst it varies the PWM power line, so the response time for the power of the glass tube to ramp up and down requires a maximum raster speed of 200mm/s to get sharp edges.

I suppose I could try a higher PWM frequency which is set to 20kHz default.

At 800mm/s at 300 DPI I have a pixel frequency not far off 10kHz. However, from the widening I get of a font when the laser is controlled by PWM and I run bidirectional, it is clear that the effective response at the laser itself is much slower, something like 1ms at a guess from the distances involved, which is what the spec sheet claims for the power supply or laser, can't remember which. I could I suppose make a massive backlash adjustment just for this mode but fine detail would be surely lost as I make a big blob or not over 10 pixels :lol:

I might try to see at what speed I need to drop it in this mode to resolve a 200 DPI on/off dither pattern.
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Joined: Mon Mar 05, 2012 1:11 pm

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