Hello everyone,
I am still learning about what my Glowforge can do. I’ve done some engraving and had some weird results. I want to use the variable power method, but when doing test strips on wood, the color didn’t seem to fade linearly as expected. That may have been partially due to the masking, but there even seemed to be an S-curve in the color instead of a linear fade. I decided to put that on the back burner, but then this weekend I was testing engraves in acrylic and realized that there really is something off here. Here is the image that I gave the Glowforge;
it’s a straight fade from black to white. The result was not a smooth fade in depth. Investigating further, I found that the most obvious errors occur between 55% and 70% power. Here are the results of engraving the previous image repeated 5 times in the same place (taking breaks in-between to cool the plastic). With each engrave, the errors became more apparent.
Those images confuse me a bit because I can’t tell exactly what I’m looking at… is that being shown with the engrave on the top side or bottom side?
It looks like the errors you are talking about are the dark areas on your second image (on the right hand side)… but it looks like the engrave went from light to dark (light on the left, dark on the right)?
Sorry about that.
We are looking down into the cut just as it sat on the crumb tray. So the deeper part, 70% power, is on the left and the the right hand side was cut 55%, I expect. does that help?
“straight fade”… someone posted a while back about the way that graphics programs create gradients being non-linear in themselves. So I am not sure if the variance you’re seeing is a result of the hardware or the image. Sorry, I cant find that post right now, but you might want to verify that your gradient is linear if you haven’t already?
Furher reading, but not the post I was thinking about. Dang, where’d that go?
You just linked it. You can get a linear gradient effect using the Blend tool in Illustrator or the Interpolate function in Inkscape. (The original from @wbgraphic.)
No tutorials on using them but they’re pretty straight up functions. (Don’t forget to rasterize your gradient when you’re done creating it.)
Hmmm. My eye dropper tool seems to verify that my gradient is linear. also I have reproduced this several times, and after measuring with calipers, the “hills” are always in the same place, so I don’t think it is a defect in the material. Did Dan have a solution or an alternate curve we should be using?
It depends on how you create it. I looked at the values in Photoshop and it seems to be linear (though I could be wrong).
One aspect of this is that it sounds that you’re squeezing in 254 values (pure white doesn’t count here) over a power range of 15-something units (we don’t know what the units are).
That helps it’s kind of an optical illusion (to me, at least).
I’m not sure on the hills. It’s hard to see what the ‘value’ of the error even is/how much error there is. I think that I would try removing the masking for sure, to eliminate a variable.
I’d also look at getting the focal height set correctly. I assume it was defocused to try and get a smoother engrave?
I know some have had success with defocusing (on acrylic), but I’m not sure if that was on 3d engraves, vector engraves, etc. It seems like a whole lot going on in one test.
Yes, I preformed several tests on two different pieces and the other results matched. I actually tested 0% to full power and a few other ranges to narrow down where the problem is.
Vary-power is meant to be used with a grayscale design. I wonder what would happen if you converted the image to an actual grayscale and tested with it, as opposed to RGB.