Medium acrylic breaking during use

Hello,

I have designed and made a simple card shoe for 5 decks that my parents wanted for a game they love to play, Hand and Foot Canasta.

They couldn’t find one they liked anywhere for purchase, enter The GlowForge.

They love using it, but it is very fragile and has broken where two pieces slot together. I made the slots tight enough that it doesn’t fall apart if you move it, but loose enough that you could still take it apart if you wanted to, so there shouldn’t have been too much pressure on the slots. They didn’t care for the draft board version…they like the acrylic much more.

I tried baking the whole thing in the oven at 180F for 3hours, then let it cool until the next morning. When I took it out of the oven, it had cracked at yet another slot joint.

Is there something I’m doing wrong? Is this stuff just that brittle and shouldn’t be used for projects that will get handled too much? Is there a better medium to use besides acrylic?

Thanks for the inpunt!

Edit - I am also using Weldon4 right now at all the slot joints to see if that helps with keeping the pieces from breaking

David

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Looks excellent! :slightly_smiling_face:

Tight slots were always a problem for me in acrylic…there are a lot of stresses in corners and they tend to split easily. (I’v never tried annealing it in the oven. That’s supposed to help.)

What did work really well is something called “dog bones” in the corners…you just place a small (very small) cutout circle in each interior corner, and it distributes the stresses so that the acrylic doesn’t crack as easily. Or you can extend the slot a bit and round the corners out slightly, but that’s a little trickier.

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You need to bring the temperature up slowly, not just dump it in a 180ºF oven. Step it up over a couple of hours (120/140/180) then back down over a couple of hours again.

That said, the rounded corners mentioned above will help relieve stress with slotted joints.
image

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I did gradually bring it up…I had the oven light on for about 30min (80F) then had the door cracked open with the oven on 180F (lowest it goes) and the temp was around the 120-130s, then I shut the door and once it hit 180, I started the 3hr timer. I did no step it back down though, just shut it off and let it sit.

I will have to try the dog bone method, seems like that should relieve quite a bit of stress in those corners.

Thanks

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Yeah… mine goes down to 90ºF… I think backing it down is as important, if not more important, than ramping it up.

I’ve rarely annealed it, however. Usually I just cut to a nice fit and then use weld-on to bond the parts. For what you’re making, I wouldn’t think there would be a lot of stress on it.

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The acrylic looks great, but if it keeps breaking maybe consider making one out of plywood and see if it is more durable.

I think the main stresses on it come from when the take it with them when they play at other couples houses.

Ah… yes, if you’re pulling it apart regularly, you probably want to have a loose fit.

I made the prototype out of draft board and it worked great, but they wanted the smooth edges of the acrylic…they are using the DB one right now as I’m trying to mend the acrylic one. They still like the acrylic better.

Try 1/4" acrylic?

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That was my next idea