How to design a 3D-printed snap closure that works perfectly?

Question

How to design a 3D-printed snap closure that works perfectly?

A

Alex Bolt

01.07.2024 at 17:38

16

Hey guys! I’m hoping I can get some technical advice in designing an enclosure for a scientific instrument — it’s a portable and remote logging device. The device I’m enclosing is about 100 mm square and maybe 20 mm high at the maximum. It has no display, it’s a data logging device, so we will get data off it via wireless after each test cycle. I’d love to make a case that snaps together, to keep metal parts like fixings to a minimum because of some rapidly changing magnetic field issues and concerns about eddy currents.

I’ll only need a small number of these for testing right now, so I need to 3D print the case, but I need to design so it will tool ok eventually. If the test results are good, the volume will follow.

Where do I start? I’ve had a play with some design ideas, but it’s impossible to validate them as our FDM printer really can’t handle either the fine detail or the strength. My snaps didn’t engage much and broke off really easily!

This is what the snaps look like, but they just break off so plz hlp!

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A

Alex Bolt

01.07.2024 at 17:38

Hey guys! I’m hoping I can get some technical advice in designing an enclosure for a scientific instrument — it’s a portable and remote logging device. The device I’m enclosing is about 100 mm square and maybe 20 mm high at the maximum. It has no display, it’s a data logging device, so we will get data off it via wireless after each test cycle. I’d love to make a case that snaps together, to keep metal parts like fixings to a minimum because of some rapidly changing magnetic field issues and concerns about eddy currents.

I’ll only need a small number of these for testing right now, so I need to 3D print the case, but I need to design so it will tool ok eventually. If the test results are good, the volume will follow.

Where do I start? I’ve had a play with some design ideas, but it’s impossible to validate them as our FDM printer really can’t handle either the fine detail or the strength. My snaps didn’t engage much and broke off really easily!

This is what the snaps look like, but they just break off so plz hlp!

0

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A

Alex Bolt

02.07.2024 at 11:04

Sarah J.

Hey Sarah. Ideally yes, we may want to open the box even though the product is ship-and-forget, collecting them and shipping them back for a second journey would be a nice option. Opening the box to recharge the battery is a bit untidy, but a charge point that we might never use seems like a waste of money.

I was assuming we would smash the case open and just re-use the PCB, but that does seem wasteful now I write the thought down!

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Sarah J.

02.07.2024 at 12:21

Alex Bolt

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!

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Alex Bolt

02.07.2024 at 13:02

Sarah J.

OK, that’s all good. Any thoughts on a quick way to ease the wall section problem? I’m thinking about length solutions, but disconnecting the post from the wall sounds messy.

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Alex Bolt

02.07.2024 at 16:59

DrewK87

I think this is what you suggested, I like it. I’ve reduced the engagement and ‘weakened’ the snap legs as well.

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DrewK87

02.07.2024 at 17:33

Alex Bolt

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.

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Alex Bolt

03.07.2024 at 09:45

DrewK87

Hey DrewK87. It is feeling nicer. Yes, the fillet felt right, and I reduced the snap by 25% or so.

I like your thinking. This is what came out of it. Thanks for your help!

0

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Hey guys! I’m hoping I can get some technical advice in designing an enclosure for a scientific instrument — it’s a portable and remote logging device. The device I’m enclosing is about 100 mm square and maybe 20 mm high at the maximum. It has no display, it’s a data logging device, so we will get data off it via wireless after each test cycle. I’d love to make a case that snaps together, to keep metal parts like fixings to a minimum because of some rapidly changing magnetic field issues and concerns about eddy currents.

I’ll only need a small number of these for testing right now, so I need to 3D print the case, but I need to design so it will tool ok eventually. If the test results are good, the volume will follow.

Where do I start? I’ve had a play with some design ideas, but it’s impossible to validate them as our FDM printer really can’t handle either the fine detail or the strength. My snaps didn’t engage much and broke off really easily!

This is what the snaps look like, but they just break off so plz hlp!

0
Hey Sarah. Ideally yes, we may want to open the box even though the product is ship-and-forget, collecting them and shipping them back for a second journey would be a nice option. Opening the box to recharge the battery is a bit untidy, but a charge point that we might never use seems like a waste of money.

I was assuming we would smash the case open and just re-use the PCB, but that does seem wasteful now I write the thought down!

0
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!

0
OK, that’s all good. Any thoughts on a quick way to ease the wall section problem? I’m thinking about length solutions, but disconnecting the post from the wall sounds messy.

0
I think this is what you suggested, I like it. I’ve reduced the engagement and ‘weakened’ the snap legs as well.

0
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.

0
Hey DrewK87. It is feeling nicer. Yes, the fillet felt right, and I reduced the snap by 25% or so.

I like your thinking. This is what came out of it. Thanks for your help!

0

Sarah J. · Answer 1

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?

DrewK87 · Answer 2

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.

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