Lighter / darker bands when engraving large "blocks" in fill mode

Couple of background notes:

This all pertains to engraving acrylic. Generally running about 300mm/s at 7% pwr. Line interval of .095 with the lens slightly out of focus.

I’m using a Thunder Laser I retrofitted from 130W laser to 50W (new tube and power supply). Running with a CW-5200 water chiller.

FWIW, all of the engravings were from left to right, bottom to top.

I have the laser on its own circuit, so there is no “interference” from any other device.

Problem 1 (resolved- I’m just posting this in case it will help someone else)- I was getting lighter bands in my engravings. The bands were approx. 1 cm in height and ran all the way from left to right. Depending on the height of the image, there were usually one or more of these bands that were fairly evenly spaced out. Turns out, whenever the chiller turned on, it would drop the tube temp VERY quickly (about a minute) which corresponded to every one of the bands. Now, instead of a water chiller, I’m using a water bucket and an “always on” pump. Those bands disappeared.

Here’s a picture of what I’m referring to:

Problem 2- NOT RESOLVED- Here’s an image for reference:

I now get a noticeably light band whenever I engrave larger, solid areas then when the engraving is “chopped up”

if anyone has any ideas, please let me know— I’m at wits end.

7% power on a 130w likely means you’re in the “unstable” band of the laser power - not uncommon with glass tubes, especially at higher wattages. Increasing the power should make it more consistent.

I probably shouldn’t have confused the issue-- but I’m actually running 50W tube and power supply (the table itself USED to be for a 130W).

Gah - I missed that bit, but it could still be the issue, depending on the tuning of the tube. Try increasing the power and going a bit faster.

I did that. Same issue— although I didn’t go much past 7.5% power because then it just engraves too deep and produces way too much dust.