Hey Alex. I hear you. FDM isn’t ideal for this kind of fine detail. I suggest you use SLS for the prototypes, as this gives you high strength and pretty good reproduction in the fine details. The biggest benefit is anisotropic properties, so you can have strength to spare in the snap features. Most suppliers carry PA12 nylon, which is good.

At first glance, this is quite a stiff box. I assume that’s a 1.6 mm PCB I can see? Helps me to scale the case. If so, I’m not surprised the snaps break, they’re pretty aggressive (which is good) but the upstand is quite short, so you’re asking for a lot of concentrated bending as it snaps.

There’s some changes I’d suggest to the snap feature, but a bit of context would help us. Q: Do you ever need to open the box?

It’s only a little elephant, we can eat it one bite at a time. How about if your snaps were not one piece, but several legs like a comb? This kills two birds – it will reduce the stiffness AND ease some of the wall thickness issues.

OK, that’s clearer. Here’s a few thoughts:

• As they stand, you have about 1mm of hook, so you’ll need to either reduce that or make the leg longer. Less hook might be a bit weak, but you don’t have heaps of space for the snap to be longer and more flexible. The filet on the case edge limits you a bit.
• Openability is a nice feature if it costs you nothing and isn’t a huge hassle in the factory.
• The snap legs are adding a chunk to the wall thickness. That’s fine when you prototype, not so much when you mold these parts — there’ll be a sink on the outside when the thickness changes.

I suggest you look at the design to tweak these aspects. And when you’re ready for prototypes, we can help you source SLS. That’s laser bonded nylon 12 (usually) and it’s a lot tougher and less isotropic than FDM, so flexing of snaps will flex and not break them so easily!

I like this, those legs look less stiff. You added filets below the snap so they’re less likely to crack. That’s nice. Did you also reduce the depth of the hook engagement, do I see?

I suggest you reduce the recess that you’re snapping into. Get it too deep and you’ll see a shadow on the outside, at the thickness change. Also fillets at the bottom of that pocket will blend the walls a bit better.