Glowforge is skipping spots when cutting

My glowforge has been giving me trouble with not cutting all the way through in some spots. It’s nothing to do with the amount of power because I’ve wasted a ton of material trying different settings. It even skips the same spots if I run it again for a second time on the same cut. When it does cut through it leaves these little etched/charred notches on the edges on the back side of the wood that almost look like they could be from the honey comb. Again, I’m certain it’s not because the power is too high or too low. Ive cleaned all my lenses several times. I don’t know what else to do, please help as I have a bunch of Christmas orders to fulfill.


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Are you using Proofgrade material? If not, I suspect you are seeing deviations in the material that is causing the not cutting through issues based on the photos. If you are using Proofgrade materials with Proofgrade settings, you should open a support ticket with Glowforge so they can investigate.

The charred spots are flashback where the laser is reflected from the grid below. It means your power is too high or your speed is too low and you are not masking. Masking helps prevent those, but with certain material and laser combinations, flashback marks on the back side aren’t avoidable. On rare occasions I have also seen the laser dwell on a certain spot long enough to heat the grid red hot and burn the material. This is usually caused by a problem with the cutting settings or with multiple small elements in the file that cause the laser to either go over a certain area multiple times in rapid succession, or start and stop in basically the same place without time for the grid and the material to cool.

If it isn’t material variation, it’s likely a file issue. Though I suspect it is the material.

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What @ben1 said is spot on. It’s definitely your material - looks like Baltic birch ply?

On my Bb ply this means I’ve hit a glue spot hidden in the layers. No amount of running the cut again will get through. Sometimes you can find these spots ahead of time by shining a very bright flashlight behind the ply in a darkish room.

As you’re making orders for other people, I’d definitely drop your power a bit and mask the back as the flashback is unsightly in a finished product.

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The charring is from flashback, no doubt. You need to mask, or cut on a piece of sacrificial material.

Not cutting thru is almost certainly a material issue, as stated above. That’s one of the benefits of Proofgrade materials, they are pretty consistent. The only attractive material I’ve found to be just as reliable is Purebond plywood from Home Depot. There are others that cut and/or engrave fine but the Purebond Maple Ply has been my go-to for a couple of years now.

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You are all correct. I went in a dark room with a flash light and saw all the heavy glue spots. I usually purchase my wood from Smokey hills but I purchased this from a random vendor on Etsy. I probably need to clean my crumb tray better as well in regards to the flash back, I’ve emptied the crumbs but it still has a film on it I just haven’t come up with a plan on how I will clean it. Thank you all for your answers.

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Cleaning the crumb tray won’t affect flashback. Flashback is either the reflection of the beam off the top surface of the grid up into the back of the part, which is solved by optimizing settings and/or masking, or burn from the grid heating up and burning the workpiece. Burning is solved with masking.

You can solve the flashback with a sacrificial layer between the grid and your workpiece but this can be dangerous. Layered materials are more likely to catch fire.

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Thank you this was very helpful info!

Do you know of a good vendor to buy the masking tape from? Every time I priced it, it was so expensive and I couldn’t justify the cost so I always just clear up my pieces with denatured alcohol, but now I have these burn arms I have to deal with

Here’s one from my Amazon order history:

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I personally don’t use materials that are bare from the manufacturer. However, Amazon has several options to choose from for wide masking tape.

Yes, it gets expensive considering you throw it away, but it’s about the best solution to your issue.

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An alternative to the tape (for flashback on the bottom) is a sheet of copy paper or even newspaper under your material. The paper gets the flashback keeping the underside of your material clean.

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