Indeed! We have exactly that planned.
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Wont you get visible artefacts if you change the focus in 0.7mm steps mid print?
Plugging numbers into the Rayleigh formula (waist 0.2mm, beam 5mm, lens focal length 50mm) I calculate the spot will increase 45% to 0.29mm at 0.5" when focused at 0.417". That gives a reduction in power density of slightly more than 2. I don’t see how that can be considered still in focus.
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I engraved some composite material tiles on Sunday that were 0.51" thick just to see what would happen. I put them on the crumb tray. The engraving was moved about a 1/2 inch or more to the left of where it should have been. From now on, if it’s over 0.475" thick, I will remove the crumb tray. Alignment has never otherwise been an issue on my machine.
Since it only supports 0.5", it’s dangerous to use thicker material because of the air assist nozzle - it might whack into your material. A hundreth of an inch probably wouldn’t be an issue but with variations in surface height you might bump into it inadvertently.
The focus of anything near 0.45" is when I do a very light score to check my placement because I’m not sure whee the focus gremlins come in 
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Yeah, it’s not worth it to attempt again for multiple reasons, including material spoilage. The tiles were free samples from EcoSupply and are only about 3" square. Very dense material and very flat. On full power at 500 speed, the GF did not cut very deep into the surface.
@scott.wiederhold, I ran a vaguely similar test using anodized aluminum, to find out just how much the beamwidth changes over the focus range. I observed a range of spot size of about 2:1, along with a notable softening of the edges of the spot.