Laser Engraving hollow objects

[Andrea Herman]

Hello, my name is Andrea and I'm the coordinator of the Innovation Lab makerspace at the Saint Paul Public Library, St. Paul, MN.
We've been open since 2016 and I've used and taught our ULS VLS3.50 since then. Weirdly, I had this question pop up twice after never coming up before.
Lab members were engraving boxes and tried to do thickness of the material rather than height of the box. The laser ended up moving on its own to the height of the object. So, it looks like you must use height rather than thickness for hollow objects, at least on the ULS VLS3.50.
The Lab members questioned whether that would make the engraving too deep. One of them had an issue where the laser burned too deep, the other did not (so that might be a coincidence). I didn’t have any issue trying it myself.
So, is there any issue or mitigation that needs to happen when engraving a hollow object?

This message has been cross-posted to other laser engraving forums.

Thanks, Andrea

[Mike Chance in Iowa]

I probably shouldn't be reading and replying while exhausted & hungry. I had to read this a few times. If I am reading this correct, let's go with a 4" tall wood hinged box that is made with 1/4" thick wood so when you open the hinge, it's hollow inside. I have not used a ULS engraver. If it behaves like other engravers, you set your focus height based on the 4" tall box. Then adjust your engrave settings to achieve the desired results. If you planned on cutting through the box top, you would still set your focus height based on the 4" tall box, but you would adjust your cut settings to be able to cut all the way through 1/4" thick wood.

What many of us do is set up a test engraving swatch on different species of wood and engrave at different shades of gray/black "squares" and at different speeds and power. That way you can look at your swatch and quickly see how deep and dark the squares engraved and what settings were used to achieve that look.

[Andrea Herman]

I probably shouldn't be reading and replying while exhausted & hungry. I had to read this a few times. If I am reading this correct, let's go with a 4" tall wood hinged box that is made with 1/4" thick wood so when you open the hinge, it's hollow inside. I have not used a ULS engraver. If it behaves like other engravers, you set your focus height based on the 4" tall box. Then adjust your engrave settings to achieve the desired results. If you planned on cutting through the box top, you would still set your focus height based on the 4" tall box, but you would adjust your cut settings to be able to cut all the way through 1/4" thick wood.

What many of us do is set up a test engraving swatch on different species of wood and engrave at different shades of gray/black "squares" and at different speeds and power. That way you can look at your swatch and quickly see how deep and dark the squares engraved and what settings were used to achieve that look.

Thanks, Mike!