Engraving Glass -What Changed

I am using an Ortur 20w laser setup. I’m trying to make some wine glasses for friends. The first 12 came out pretty well. But then…

The settings are speed 800 mm/m and power 40%. I coat the glasses with Rustoleum Cold Galvanizing Compound. The glass surface is leveled as best I can get it. Focus is at 29 mm.

The first photo shows that the glass has a lot of soot where the laser burned.


The second photo shows how it looks after clean-up. Nothing on the right side engraved but the left side gets better.

The third photo show what it is supposed to look like although it is not perfect either.


I did clean the lens, it was dirty but the engraving did not change.

I am very confused about where I went wrong. What does the community think I need to do to get things right?

IMHO, I think you are not keeping the laser focused… Seems like it burns in the middle and is light at the top and bottom.

Shorter the lens, the less depth of field for your ‘dot’…

:smile_cat:

I really appreciate your thoughts on this problem. What I did was bump the power up to 75% and that solved the problem. I’m not sure why 40% worked on the first set of glasses but not the last. I suppose my laser could be losing power. I’ll need to check and see how it does with wood. Thanks again Jack.

Did it not retain the ‘burn’ middle with a higher power?

Good luck

:smile_cat:

It burned the paint in random areas but the engraving turned out pretty good. I’m happy.

Are you sure there wasn’t some sort of film/contamination on the glass? Did you wipe them down with DNA before applying the coating? Were all the glasses from the same box or did you pick them randomly off the store shelf and thus they could be from different production batches?

Doug, yes I did wipe everything with DNA before painting. The glasses were off the shelf at the 99 cent store. That should tell you something. I think the fact I’m using an inexpensive laser with cheap glass could be part of the issue. What type of glass is best for engraving?