Chinese Laser Engraving Notes

[Keith Winter]

I've been having a lot of fun working on the new chinese laser. Much different than the US ones. One thing I've noticed is the Chinese laser has little lines in it in between each row, and/or where they overlap (in my limited testing). See my attached photo, this is what I was able to get it after some tweaking. If you look very closely you can see the little lines where each row of the beam meets. **NOTE: The built in camera of my phone smooths some of them out so they are harder to see in the photo than in person.** Using a 2" lens at 800 speed here.

The best results I've gotten so far at with X direction engraving (tired x_unilateralism but took 2x as long and didn't look much better) 800 speed and 0.08 interval @ 30 power (about 45% of max power) seemed to be the best looking setting so far. 0.09 interval also looked very comparable on larger letters and saved 20% on the time over 0.08 interval.

Here are my tests and notes. I hope by comparing notes we can all help each other get better. Any other settings you've tried which helps you get better engravings than these on your Chinese laser?

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[Dave Sheldrake]

600 speed, 0.1 scan gap, 20% power mate, that tube will be pumping about 145-155 watts when new so reducing the amount of heat getting into the job will help :)

[Bill Carruthers]

I've been having a lot of fun working on the new chinese laser. Much different than the US ones. One thing I've noticed is the Chinese laser has little lines in it in between each row, and/or where they overlap (in my limited testing). See my attached photo, this is what I was able to get it after some tweaking. If you look very closely you can see the little lines where each row of the beam meets. **NOTE: The built in camera of my phone smooths some of them out so they are harder to see in the photo than in person.** Using a 2" lens at 800 speed here.

The best results I've gotten so far at with X direction engraving (tired x_unilateralism but took 2x as long and didn't look much better) 800 speed and 0.08 interval @ 30 power (about 45% of max power) seemed to be the best looking setting so far. 0.09 interval also looked very comparable on larger letters and saved 20% on the time over 0.08 interval.

Here are my tests and notes. I hope by comparing notes we can all help each other get better. Any other settings you've tried which helps you get better engravings than these on your Chinese laser?

323840323841
Keith - the Chinese machines don't use the PPI or DPI settings like the mainstream ones do.The nearest equivalent equivalent setting in the RDCam and Lasercut software is often called the Scan Gap or in your case "interval". Which effectively is the measure of movement of each step of the Y axis. The Scan Gap to DPI ratio is 100DPI = 0.254 scan gap. So if you want finer "lines" or more DPI try setting your interval to something like .042 which is approximately 600DPI. Quite a few of the Chinese machines come with a standard of .08 interval which is roughly 300 DPI in American terms.
Cheers

[Keith Winter]

Keith - the Chinese machines don't use the PPI or DPI settings like the mainstream ones do.The nearest equivalent equivalent setting in the RDCam and Lasercut software is often called the Scan Gap or in your case "interval". Which effectively is the measure of movement of each step of the Y axis. The Scan Gap to DPI ratio is 100DPI = 0.254 scan gap. So if you want finer "lines" or more DPI try setting your interval to something like .042 which is approximately 600DPI. Quite a few of the Chinese machines come with a standard of .08 interval which is roughly 300 DPI in American terms.
Cheers

Excellent explaination, thanks for that Bill! I didn't know what the relationship was to dpi. I had figured out that it slowed the laser and appeared to make the lines closer together, making it look better :D Pretty happy with the .08 -.09 on wood so far. Which you said is about 300 dpi, and consequently the same resolution I run wood at on a Trotec. :)

[Kev Williams]

here's a gap to lines per inch reference (with some rounding ;) ) followed by scan gap in inches:

.20 = 127 / .0079
.19 = 135 / .0074
.18 = 141 / .0071
.17 = 149 / .0067
.16 = 158 / .0063
.15 = 169 / .0059 << .006 beam begins to overlap (typical Chinese machine)
.14 = 182 / .0055
.13 = 196 / .0051
.12 = 213 / .0047 << .005 beam begins to overlap (typical Western machine)
.11 = 232 / .0043
.10 = 256 / .0039
.09 = 286 / .0035
.08 = 322 / .0031
.07 = 370 / .0027
.06 = 417 / .0024
.05 = 500 / .002
.04 = 625 / .0016
.03 = 833 / .0012
.02 = 1282 / .0008

[Keith Winter]

Ok I've applied some of the tips you guys gave me and also some things I've read and here are the results. Here is a comparison of my 80 watt Trotec vs the 130 watt Thunder Chinese Laser

Top is a Speedy 80watt 5 minutes 38 seconds 55% speed 100% power
Bottom is my 130watt Thunder Chinese laser 12 minutes 27 seconds 0.07 interval 800 speed 27 power (about 20% of my max power)


Some notes:
1) If you look closely you will see the wood grain in the Trotec, in the Chinese you see little lines instead of the wood grain. Running at 0.07 interval it should be similar to the 333 dpi of the Trotec from what has been said. The Chinese is very acceptable, but you can see the Trotec is much smoother
2) That being said... I've read that the 130w Chinese might be at a disadvantage on resolution because a 130w Chinese beam is fatter than a 80w. So if I had a 80w the chinese engraving might be sharper. Is that correct?
3) 2.5" lens on the Trotec. 2" lens on the Chinese


Third Photo I have a question on.
I'm trying to figure out how to make a stained piece of wood come out the wood grain color (this is maple so it should be a light yellow) instead of burned colored when using my Chinese laser. I can adjust my PPI/HZ on my Trotec to do this, but I am told Chinese don't have this.

How do you guys compensate (besides turning down the power and losing depth) so it doesn't burn the wood and instead exposes the color underneath on a stained piece? (Note: Most of the "white" you see is just dust from the air assist in this photo, the actual engraved area is burnt wood colored if you look closely)

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[Ron Gosnell]

Hi Keith,
I'm sorry I missed this post. I had computer troubles and am now catching up on older posts.

I think it's great that you tested so many settings and posted your results.
Your engravings on the thunderlaser are very similar to mine.
I really love the way it darkens the wood but I still get the little lines too.

I never had a trotec to compare with but I think overall the thunderlaser does a pretty decent job engraving.
I really love the way it cuts. I thought about defocusing a little to see if it would smooth out the lines
but never got around to it yet.

Gozzie

[Kev Williams]

I am of the opinion the lines are the result of the glass laser being 'always on' vs. an RF laser being pulsed. I liken the difference to the 'precision' method of hand-shoveling a narrow ditch by removing the top 2" of some topsoil with careful, equal scoops (pulsed) vs. the more barbaric method of just dragging the shovel along the topsoil to create the same ditch ;)

Each pulse of an RF laser is pretty much equal, and the gaps between pulses, small as they are, buffer the laser's effect on the substrate, like dithering. But drag an always-on laser beam thru the substrate and you can see every path the beam took...

I've been going to try and fool my Triumph into pulsing the beam by creating 80% black art and letting the engraving program small-dot halftone it. Just haven't had much play-time to try, and I'm not sure the results would be all that great anyway, I just don't think a glass laser reacts fast enough...

[Keith Winter]

Great explanation Kev, makes sense and clarifies why the Rf engraving looks better than the Chinese laser. Thanks for this!

So expanding the ditch analogy and applying it to light colored engaging on dark materials... the spreading of the pulses ( ppi) is what makes the engraving appear lighter when you use lower ppi on a us Rf based Laser. And since the Chinese lasers are more of a shovel as you said they have no way of spreading that pulse so the darkness of the engraving cannot be changed except with power. I will never be able to get a light colored engraving on a dark surface with a Chinese laser correct?

[Ron Gosnell]

It sounds like playing with dithering could be be an answer.
Like Kev says I wonder if the glass tubes would be fast enough.

Gozzie

[john banks]

Can you try less power? I am sure I read something along the lines of the RECI tubes being fastest at around 10% power, not sure if EFR are the same. For 800mm/s and the power level you are using as well as the power of your tube it looks like the edges are good. Both our original 100W RECI and our spare splatter when turning off from high power and at higher speeds this can show up on some materials. http://www.sawmillcreek.org/showthread.php?182330-Wondering-about-upgrading-Chinese-x-axis-from-stepper-to-servo

[Keith Winter]

That's at 27 power, the lowest it will go I think I use very slightly less power but the beam quality/power degrades quickly in the low 20s and finally just stops working. Mine won't even fire at 10% power as you suggest.

As far as speed, I can run at 1000mm/s without much issue except in fine detail areas I need to slow to 800 in limited testing so far. However in my testing staying at 800mm/s is actually faster than 1000mm/s unless the engraved area is extremely long because of the increased slop/overshot of the head due the increased speed. Strange little quirk there.... :)