Thanks all!
You realize that you won’t be able to engrave those on the Glowforge? They are either polished or chrome plated steel and the laser won’t touch it. You will also run the risk of damaging the laser from the reflection.
You may be able to mark them with Cermark or another method, but direct engraving will not work with this material.
You may not need a jig. Obviously you have no worries with a jig, but you may find the preview in the GFUI to be satisfactory. Once you have your unit up and printing, test placement with some scrap. I can usually do it in mine. An accurate thickness measurement of the hand warmer is critical.
As ben1 mentioned, I’ve read that chrome, like copper, is an IR reflector. That said, there are plenty of shiny finishes that aren’t actually chrome. Perhaps the Zippo website has more info.
Not arguing, but not sure what you mean here?
My bed depth is 1.4" and I have never had a problem shimming up thick items into the focus range (did a 0.7" cutting board just yesterday). I personally have never seen a difference in placement accuracy between objects on the crumb tray and those correctly shimmed and measured. YMMV, obviously.
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I know they make colored ones. Might be able to vaporize the color coating. But, yeah, definitely won’t be able to directly engrave the chrome version. Cermark would definitely be the only answer there.
Because you have to measure from the tray to the floor, then the lip of the tray, then your stack of stuff to get the item in range you introduce a lot of measuring error. And since the placement accuracy rests on that number I find that my camera placement suffers significantly compared to when I’m using the tray.
Why glowforge don’t include the tray height with each glowforge I have no idea; it would save a bunch of fiddly measuring and they must measure it to set the glowforge during testing.
Worth re-mentioning…
I’d imagine you can get pretty dang close by saying “crumb trays are xx height”. But if you want it down to the 8-10 thousandths range, you’ll probably have to bust out come calipers.
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And if at a loss for what “stuff” might be, a ream of office paper will give you thousandths of an inch increments.
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We also all have a laser cutter and can cut awfully accurate spacer boxes/feet/whatever, if accuracy is that critical…
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But a ream of paper is quick and easy!
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Yes but a laser is fiddly and expensive! Why do things the easy way when you can SUPER over engineer it?
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I use a stack of spare 1/8th and 1/4" Baltic Birch squares (12x12) I have hanging around. That gives me 1/8" increments which has been plenty. I have saved a specific spoil board for the top one because when cutting through your project it’s gonna at least mark (& often more than mark 
)the top of your spacer stack.
@evansd2 mine comes out ~0.100 higher than that one so… good enough? (hint: no). and needing to use the laser to make a jig to hold the item is exactly what the OP was asking about; which I already said that I do for things without the crumb tray because I’m not satisfied with the camera accuracy in those cases.
@Scott.Burns yes… that would be labelled under “stuff”… my reams of paper don’t add up and tell me measurements automatically. I have to put my calipers on them, thus measurement error.
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Same here – I mic’ed each one and penciled the thickness on both sides. I also keep stacks of ceramic tiles likewise marked. 1/8 inch (3,2mm) granularity works for all my use cases, since the focus range is between 0 and 0.499" (as of January 2018).
That’s definitely going in the 'hopper. 
PS – I’m curious as to the variation in crumb tray heights. My PRU was 1.38" and my Basic is 1.39." Can’t recall seeing anyone report one outside of 1.36 to 1.40, but I could very well have missed some reports. (Currently hovering around 2,400 unread.)
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mine was 0.14 something when I measured it the other day (lost the note I had it on cleaning) but I’m not at home so can’t check my spreadsheet.
even if it is 1.40 vs 1.36 a 0.04 difference is going to cause accuracy issues that I would be unhappy with on most of my projects.
Wasn’t suggesting otherwise.
I got that, i was just stating it to illustrate what would effect my use.
I am very happy with the camera for things on the crumb tray though. I was sceptical but being able to simply mark the middle of things and drag them in place is awesome compared to placing them in a specific place on an art board and going from a corner.
The Glowforge motto!
Let’s face it, none of us would be here if we chose the easy way…
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