Engraving on an uneven surface

I have seen some posts on engraving on a curved surface, but my situation is a bit different…

I’m trying to similar to a drink coaster, but larger. The idea is that I am going to use the CNC to make a circular “pocket” where you would set your drink. However, after I do that, I’m going to engrave the whole thing, both the main face of the wood, and, ideally, the circular “pocket” in one pass.

How big of a problem would this be since the “pocket” is sunken down more than the face of the board? Does this pose a safety hazard because at this point the laser is out of focus compared to the main part of the board being engraved (I read on another post that unfocused laser + wood = fire)? How much of a difference is generally unacceptable? 1/8", 1/4", 1/2"?

Below is a photo of the wood prior to engraving, just ignore the handles on the sides. Thanks!

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Experiment. If you set the focus height ~ halfway between the two, it will look the same. If you set it to one or the other, then one will be sharp and the other slightly less. Many people use intentional defocus.

It’s certainly not going to burst into flames. Not sure where you got that nugget but it’s absolutely wrong.

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If the total thickness is less than 0.5" you’ll be able to do it without taking the crumb tray out. Overall, you want both surfaces to be within 0.5" of the head when you engrave them.

And I’ll add a caveat to @eflyguy’s statement – if you soak it with gasoline first, it WILL burst into flames. But otherwise you should be okay. :stuck_out_tongue_winking_eye:

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Why can’t you do two separate engraves? One for the “holes” and one for the original board surface? As long as you do not disturb the work piece between each engrave session you should get what you want—using two difference laser focus points. The assumption is that your “artwork” would contain both engraves, with alternate ones “ignored”. Does that make sense? :sunglasses:

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Thank you everyone. I will definitely do some tests at either the height of the indent, height of the board and halfway in-between and see what I like. @lightner, yes, doing separate engraves is something I was thinking about doing, however, I was thinking that if there is really a noticeable difference between in focus and out of focus and if I am not perfectly aligned to the indents to begin with, there might be a bit of a difference right at the edge where I misaligned. But I might play with that too. I also need to learn some Inkscape skills to “cut” my artwork into two pieces with a circle as my “cutting” tool :slight_smile:

Thanks!

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