Perfect alignment on a piece that is 3/4" thick

Hello, I need to do some CNC cuts on a 11x19 piece of 3/4" wood before I put it in the laser. I know that I’ll need to remove the crumb tray which I’ve done before using these tricks: Tutorial: How to cut without the Crumb Tray (Honeycomb) and I love the idea of doing the alignment setup per this: Perfect Alignment with the Glowforge from @john11.

But has anyone had success doing both, i.e. doing perfect alignment on a piece that has the crumb tray removed?

My only idea is to a.) take out the crumb tray and put in another board that is thinner per the first link, then b.) do the paper method from @john11 even though the focus will be way off (because the paper now will be way beyond the 0.4 or so max focus range and then c.) put my piece on the paper and thinner “crumb tray” piece. The only concern here is whether the laser on the paper will be so wildly off because it is outside the 0.4 or so focus max but maybe that doesn’t matter?


I have certainly lasered items off my CNC without the crumb tray. Not sure exactly what you are describing, but the top of the work needs to be within the focus range (defocused laser + wood = fire). I mean if you place a 1" block on the bottom of the laser and place your piece on top of that it will be the equivalent of 25" proud of the crumb tray height. Of course use the set focus command to get it right. Then the optical alignment should be dead on (of course if your stock piece is a wild surface then the set focus won’t get a consistent height and so the optical alignment won’t work exactly…


I’m also struggling to understand the question. The machine can align just as well on 1/8" material as 2" material.

Sorry for the confusion. My goal in this is to align the laser to the material left/right/up/down as perfectly as possible and I don’t want to rely entirely on the camera to do that. The video from @john11 seems flawless to do this, but I don’t think I have the luxury of burning the paper and then my 3/4" board without moving anything because the focus be out of range for either the paper or the 3/4" board. So I’m just wondering if others have come up with a creative solution with a jig or other solutions for something like this.


One way to do it is to put some masking on your piece and run a very light score around the circumference of your art work. It will mark the masking but not the wood and allow you to see if you need further adjustment. When you’re happy, go with throttle up.

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If you have run the Alignment setup so the math from the camera is correct, and the top of your work is above where the top of the crumb tray was then set focus will align the camera to your work, I routinely get under a millimeter off, usually less. However if you run a very light score, even outside your work you can determine the accuracy providing all elevations are the same.

If you are going to cut the piece out with the CNC, leave the outside with it in the tray and use that as a test?

I completely understand the dilemma. ha! I’d have to think about this a little more… but if I was in a bind, here’s how I would approach it. I’d place a sacrificial 1/16" piece of clear acrylic on top of your board (with the crumb tray removed). Then, I’d score the outline of the shape onto the acrylic. You’ll see your board under the acrylic. Then, based on where the line ended up, you might need to budget your board slightly and rerun the scoring. It should take about 3-4 attempts to get it right. Once, you’re spot on you can remove the acrylic sheet and do the actual engraving. If I think of a better way, I’ll let you know… I’ve used this technique before when engraving knife handles or weird/not-flat shapes. I started filming a Glowforge course and I’ll be sure to find a better way to do this :slight_smile: Also, don’t forget the No Math tool: No-Math Focus Ruler - it makes everything much easier.

Thank you all for the notes. So, @rbtdanforth, I unfortunately need to do my CNC before the laser, though I wish I could do the reverse for sure as this solves this whole problem. @john11, this acrylic idea sounds really good. I will have to do about 10 of these jobs, so maybe after I do the acrylic test, I can put some tape in the bottom of the glowforge so I know where I put my board perfectly so when I do the next one, I know where it goes each time. I’ll also check out the no-math ruler, and plus, I do need to do the alignment setup too - still never gotten around to that.


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Do that and most other alignment problems go away.:smiley:

This brings up a very good point by the way…The project I’m working on is basically 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? How much of a difference is generally unacceptable? 1/8", 1/4", 1/2"?


There is a part hanging down from the fan in the back that will hit anything standing more than a half inch above the level of the crumb tray even if the engraving is at a better distance, and It will not recognise anything below the level of the crumb tray, So if you work without the crumb tray you would still be limited to those distances and you would need a jig to hold it in all three dimensions precisely, Having done that it would not be too much to just run each level separately. If you were doing dozens of them, the bottoms cut all at once and then the tops done all at once (switching them out but leaving the settings) would be the way to go.

Makes sense, thanks.

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