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Melissa BurnerMN
07-20-2018, 12:13 PM
So I have an 80 watt AP Laser. I user CorelDraw X8, Photograv 5, and lasercut 5.3. Lately I've been experiencing this issue on my engravings.
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Above is what it looks like simulated in Lasercut

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Above is what it looks like when engraved on granite.

I made test runs with the same photo on some tile and this did not happen. One time that it did happen previously I was able to invert the color in Lasercut and the "double" lasering went away.
It looks like this part of the engraving file has a second layer but it shouldn't.
Any ideas? Any help?

Kev Williams
07-20-2018, 5:52 PM
I took your simulated image, copied it, then pasted into Corel Photo-Paint.
Then using the 'image' tab, I scrolled down to "split channels to CYMK"-

These are the results--
Magenta:
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Yellow:
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Black:
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---Cyan was pure white--

-- If you invert these, they'll appear almost identical to your granite test... So it appears the problem is with the image, not the laser, as it output a pretty faithful rendition of the average 2-bit color scheme...

FWIW, I use the 'split channel' function in Photo-Paint almost every day, as it's great for separating colors before attempting a trace, and also provides a fairly accurate rendition of what the laser software actually "sees"...

Melissa BurnerMN
07-23-2018, 7:20 AM
It's just the "whole" thing though. I was running tests on just the photo instead of the whole piece and it didn't do this at all.

Melissa BurnerMN
07-23-2018, 10:52 AM
And I decided to move on and try one of my next pieces. And it does it with this photo also.

Ray Scott
09-25-2018, 11:29 PM
I have found a few key factors in working with engraving onto granite.
1) Make sure to use a fair DPI, Scan-Gao, Interval.. appropriate to the granite or wood. I found that granite produces nice images at 180 DPI. This might seem like low resolution, but you should try it.
2) Process the photo to become a DPI that is appropriate for the material. Many photos can be resampled, and processed to produce a DPI from 50 to 500. The final image should a Black/white image ready for engraving.
3) make sure the laser scan mode uses that same DPI value. The terms DPI, scan-gap, interval, and step-over are quite closely related. You need to ensure that the laser is sweeping one laser scan for exactly one row of pixels. If your photo has 300 DPI and your laser is set for 350 DPI, then your resulting image will become something of a moire’ pattern.
4) Don’t use too much power as an attempt to get more contrast. If the contrast doesn’t pop out at you, then you can consider using a color agent to fill the lasered cracks.
5) Tune the stepper amplifiers to match the motors. It is all too often that the stepper amplifier is delivering too much current for the stepper motor. We need to remember that the stepper amplifier is also creating fractional distances between the natural motor poles as a way of micro steps. It is better to use some gear reducers and some micro-stepper. Please don’t try to use 1/64 micro steps. Using too little amperage in the step driver will result in sloppy positioning. Using too much amperage in the step driver will result in the motor always pulling tighter to the pole position. With correct amperage, the step driver will move the motor in equidistant intervals (micro steps) between the natural poles.
6). Don’t try to scan too fast. The laser needs more time to heat and shatter the granite divot. I think that a scan speed of 300 mm/second works good for my laser.

I hope this helps everyone. It is just a bit of my experience and opinion.

Kev Williams
09-26-2018, 12:26 AM
I don't engrave granite much (like 3 times ever) but I do a lot of photos on leather, some on wood, and I've found 200 dpi works well with my metal lasers. To get decent photos on my Triumph I've found the 200 dpi 'convert to bitmap' in Corel works pretty good. From there I use a .18mm gap to engrave which works out to 143 dpi, and I get good results. However, across long expanses I'll get the goofy moire' stuff -- I like the .18 gap because it's fast and looks good, but I should try a .127mm gap which would match the 200 dpi. Or go the other way, reduce the finished size to 71.5% of original, make that a 200 dpi bitmap, then increase the size by 39.8%, which (if I did it right) will bring the image back to original size at 143 dpi... :)

-anyway, keeping the dpi's the same does make sense! Someday I might actually engrave a decent photo on glass! ;)

Stepper driver amps, that's out of my wheelhouse! :D