Snapmark for double-sided cut and fixing failed cuts

Some three-ish years ago I was envisioning that brilliance of the computing power+optics sorcery that would allow my glowforge to recognize what I was cutting when I flipped it over to cut from the other side. The shape of the object would be the registration or something…

Yeah. It doesn’t go quite that slick, and the double-sided cut - as advertised - isn’t quite here yet. But you can do it with snapmarks, which means you can creatively do it with a jig taped/pinned/magnet secured to your bed.

This realization came dawning upon me as I looked at a stack of 25 bad cuts. Sometimes cuts don’t go all the way through, whether due to knots or voids in the material, or because my laser really needed to be cleaned and I didn’t know about how to clean the mirror inside the head. (yep - 16 months of use without a wipe-off. Youch.)

I’m making 200 flat-pack business card display stands for a client, engraved both sides with fiddly little cutouts. And there was a stack of 25ish wasted quarter sheets staring at me.

My baltic birch isn’t as slick as :glowforge: :proofgrade: materials; but the client can’t afford proofgrade. Because of my cleaning problems, I had surpassed an acceptable rate of bad cuts. And we know what some folks in this community think about wasted material

“Hmmm,” I said to myself. I am using snapmarks on this project already.
Time to make a snapmark variation jig that will allow me to cut from the back of these failed prints. (I wanted to re-cut from the back for multiple reasons: less smoke and flashback than coming back through from the same side, running into the same knots, charring the sides of existing cuts, sub-milimeter variance is still visible when going on the same lines… it just seems like a better fix to sneak in from behind.)

BOOM. That pile of wasted material from bad cuts? It’s been converted to the good stack.
It took some time; but I actually assigned a different color to each little square, so that in a piece that needs only one or two little rectangles to be knocked back through, I only cut that box out. Seems tedious; but then it’s a 6-8 second cut to fix the problem, rather than several minutes for the entire design, and again, less charring and flashback.

I am going to use this process to get through 1/4" BB ply, which has been a problem for my Basic model all along.

I’ll probably use this for registration of that 1/4" ply.

So there it is, another use case for snapmarks.


Solution 1 - masking - unless you want to do a lot of sanding. (i am bad about this)masking on the bottom will block flashback.

Solution 2 - also not either any - the mirror is under the top of the head (lift out the blue thing) I am sure someone will give the link to the complete cleaning regime.

Solution 3 - make sure your base point is correct like a specific corner and then “weld” it in place with pins. I have a C-Pap hose on my shop vac that has rubber ends. This makes it great for sucking up nubbins but it also provides a way to lift out finished cuts. If it does not lift out it is not finished cutting, then if you have cut and engraved each side you can just flip them and set the cut on ignore.
meanwhile all those “almost cut through” that you freed up will also fit in those holes.

Solution 5 - create a file that just engraves a wide rectangle near the very front
and set force to zero and slow speed and bend over the Glowforge and watch the fan you can barely see except in such a circumstance. If it is ever not spinning, then it is not blowing smoke away from where the laser is trying to cut, and when trying to cut its way through a lot of smoke it is not cutting your wood.


FWIW (and slightly on-topic) with BB ply, especially quarter-inch, I’ve found that some of the fillers used by some suppliers are essentially laser-proof. Since fill is randomly distributed through the core, each sheet is unpredictable – maybe it’ll laser fine, maybe it won’t, maybe it’ll just have a problem spot or two (inevitably right where you need a perfect cut).

My solution, which only works for those situations where you don’t mind some cosmetic impairment (eg: for a piece that’ll be structural), I run a job that cuts a grid of dots (I use a 1" pattern) all across the piece at full power.

…take the board out, flip it over, and you can see any areas where the laser failed to penetrate. I circle these in pencil, then put the board back into the laser (now with the marked side up), load my actual cut file, and position it in the GFUI to avoid any circled areas.

This does create more “waste” in that there are going to be parts of the board that I don’t even attempt to cut, but it does ensure that my intended part can be cut successfully (thereby removing one source of waste).

I don’t know what’s in some of the BB fillers/glues, but it can be utterly impervious. Many passes, much smoke, no penetration. Like it’s made of aluminum or something.


There’s also this technique from @evansd2:



I would like to have a list of such sources so we could avoid them or conversely a list that we can be sure they are not that. Unfortunately having an MDF center is not an improvement in my book.

This was Home Depot and I have not had a second try from them as a result.

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Wow, that works really well with a good laser pointer in 1/8 birch ply. Unfortunately not in anything else I tried or even 1/4 birch ply.

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I discovered a good laser pointer will also do great at finding leaks as it lights up the slightest smoke.

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i really haven’t had much problem with actual BB and messed up filler. but there’s definitely a difference between quality BB and generic birch ply.

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