You just have to be careful. I have some smaller ones that are really easy to shatter. If they slip, you can pretty much guarantee they are toast. The big ones I linked I really like. Plenty strong, and easier to keep hold of Haven’t broken one of those yet.
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There are different ones. I use those thin ones for leather, paper etc. I use the thicker version for wood. I also have the bar version which I can tuck in the margins a bit better sometimes when I’m doing something where the pattern would otherwise overlap the larger circular magnets. The bar ones are more powerful though so you have to be more careful that you pick up the wood piece off the bed and slide the bar into your hand.
The dime sized ones are good but you need more to flatten a warp and they’re harder to grab and get leverage with your fingers (usually folks wrap them in a painters tape wrap like a blue Hershey Kiss 
).
I store mine on the side of my Glowforge stand (Husky tool storage cabinet) with the white plastic spacers they come with. Then it’s pretty easy to slide one off to put on the material. The thicker ones can jump from the front of the GF to the back if you’ve got something metal on top of the GF side 
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I have some of those disk ones but was actually thinking of getting the ones with the hook on the end so I can move them easier… they are too freaking strong
Careful with the magnets that have hooks. Remember, material thickness +magnet thickness+hook can only be so tall before impacting the air assist port.
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I forgot about that, what amount of clearance is there?
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Bingo! That’s why I keep them under 1/4" and I don’t use the Hershey Kiss taped ones on the GF. Bar ones are great where you need more power (traditionally thickness) but don’t want thicker disc - you spread it out over the length of the bar (& I think there’s some physics around rectangular magnets being stronger than circular ones).
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Interesting, I reported a similar issue. Bottom left corner failed to cut. Another theory I have… were you cutting a lot prior to this cut? I feel like the laser lowers in power as it heats up to avoid overheating, and is perhaps a bit overzealous in its guessing resulting in lowering power too much to maintain cuts.
I doubt it does that but I think if the temperature rises power will fall off as the tube gets less efficient.
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I think the net result is the same, the overheating protection should kick on prior to the laser failing to laser.
It should certainly stop before it reduces the tube life. If power falls before that happens it should increase the power to compensate so that the cut succeeds. If it can’t do that it should pause with the fans on full to cool.
assuming this is actually the reason anyway, maybe the bottom left corner of glowforges are like the bermuda triangle of photons.
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How did I miss the whole changing focus to compensate for cuts not going through? I would have loved to try this out on my pre-release before I shipped it back to see if it was a focal issue or a power issue. Never thought of it. I just drop speed down 8-10 gnat butts per second and then I don’t worry.
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Maybe, but I haven’t noticed that. This was on first cuts from power off, pretty cool temperatures. I think it’s definitely warp that’s causing it. Look at your board, I get it is visibly curved. If I tape a corner down to the table, the other corner lifts surprisingly high. I ordered some of those magnets.
Gnat butts? ROFL! 
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@dan said in his SMMF talk that the ability to cut all the way through material is due to the laser light experiencing total internal reflection within the kerf.
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Lee Valley sells some that come with special instructions for separating. I’ve got a few of those for the really serious warps. (Years ago I worked briefly at a wind turbine company – the generator assembly area was no go except for the handful of people who had been trained to operate the magnet-moving equipment 
)
These are the magnets I have always used to hold wood very flat. Extremely strong, about the size of a quarter. Fairly thin so they don’t impact the air assist port, BUT… they are powerful. You need reasonably strong fingers and need to be careful not to get skin between two of them. I slide them off the material rather than try to lift them when possible. Will hold anything perfectly flat. For lighter material I use the same type of magnets but much smaller in diameter.
https://www.sciplus.com/p/1-INCH-DISK-MAGNET_46712
There are a bunch of different sizes on the site.
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Thanks for all the great work done here. Your Glowforge can print successfully on materials with some warp, but here are some tips to reduce it.
Give your materials time to flatten
- Humidity and heat from shipping and printing may cause your materials to temporarily warp. If this occurs, unwrap them and store them, per the instructions below. They will relax, and their warp will lessen over the course of about a week.
Store your material carefully
-
Upon arrival, immediately store your materials in a cool, shaded, dry place
-
Stack materials on a clean surface. Stacking warped material on top of other warped material can make the problem worse.
-
To prevent discoloration or damage, keep them out of direct sunlight
-
If your materials need to be stored in a humid area, wrap them with plastic wrap or shrink wrap to keep moisture out
Set heavy objects on top of your material
-
To ensure your materials stay flat, stack heavy objects on top of your materials
-
Distribute weight evenly on top of the material. If possible, use a flat object like a textbook.
If your material is so warped that it cannot print successfully and these suggestions don’t help, please make a new post and let us know. Thanks!