Looking for suggestions: lock/snap/join real parts

[Anonymous]

Hi folks, I need some help and/or ideas here. I'm looking for an easy way to get to 3D printed parts to be able to get "locked" together, or "snapped" together, while allowing for them to be separated again later. Attached is an assembly file with related IPT files. There's a bottom piece and a top piece and the two of them need to stick together. The inner cavity will have other stuff in it, so I can't add anything extra there. I don't want to introduce screws either, just some way for these parts to lock together.

I considered just using friction to join the pieces but over time, the plastic will start to wear and the fit will start to loosen up. These two pieces also rotate together on a bearing, both clock and counterclock, so I have to keep in mind that there will be some minor twisting between the two - they have to remain "stuck" together.

I also have to keep in mind that they are being 3D printed and things like overhangs can be a bit problematic depending on how big. Ideally I'd stay away from that but I'm willing to entertain possible solutions.

Like I said, I'm looking for ideas here. So post them, whatever they are, and I'll see if I can work with any of them for this specific application.

[-niels-]

A disclaimer beforehand: I have no knowledge of plastic part or 3D printing, so this might be a horrible idea.

That being said, i'd try something like you see in a lot of casings that don't come apart anymore without forcing them a bit.

Add a few locking extrusions and cavities...

[mcgyvr · Accepted solution]

I gotcha niels..  I do plastic design/3d printing all the time now.. Ultimaker 2 printer.. and have 15+ real injection molded parts designed under my belt so far..

Just do a bump around it and matching reverse in the other part..

and if you ever go to a real injection mold it can be done 

http://www.protolabs.com/resources/injection-molding-design-tips/united-states/2010-03/default.htm

[mcgyvr]

TONS of examples/books,etc... if you simply google "plastic snap fit design"

This is a great book.. (sample chapter)

http://www.hanserpublications.com/SampleChapters/9781569903889_9781569903889_The%20First%20Snap-Fit%...

and another here (most of the plastic suppliers have great design guides to follow,etc...)

http://www2.basf.us//PLASTICSWEB/displayanyfile?id=0901a5e1801499d5

[mcgyvr]

one question..

How do you expect this area to print as its an overhang? area in orange... printed supports?

It will print much better if you can chamfer it like this.. (if the design allows for that)

[Anonymous]

It actually prints surprisingly well because the overhang isn't that far. I can't chamfer it because that's where a bearing (red) will fit in.

[Anonymous]

So originally I designed it like this:

However that proved to be difficult to take apart. Once snapped into place, that was it, there's no separating it. The only way I was able to open it back up was because I didn't have the upper "lens" in place so I was able to shove my finger in the whole thing and push really hard. Once that lens is in place though, I wouldn't be able to do that anymore. This is why I need to find a diferent way of doing it. With your bump or bead idea, which will also "snap" into the matching groove, how easy would that end up being be to separate later? (I need more coffee)

[mcgyvr]

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With your bump or bead idea, which will also "snap" into the matching groove, how easy would that end up being be to separate later? (I need more coffee)

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Insertion/separation force will be dictacted by the bump size and the material properties... So do a trial/error process till you find what works for your application.

What you did is VERY similar though..

You "may" be able to do this too depending on intent to reduce the force required..

[Anonymous]

Yeah no, I can't add slits to that outer shell. 🙂 Though it makes me wonder if I can do it internally, on the bottom part. Hmm, time to do some testing. FYI, I also have a UM2. It's my little work beast.

[mcgyvr]

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@Anonymous wrote:

Yeah no, I can't add slits to that outer shell. 🙂 Though it makes me wonder if I can do it internally, on the bottom part. Hmm, time to do some testing. FYI, I also have a UM2. It's my little work beast.

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You could actually only do partial revolutions of the bump on the bottom part (but full revolution on the other piece so its non-directional).. That would take much less force too..

Like this

[Anonymous]

Yep, I was just thinking about that. For that matter, that inner "ring" where the bumps are on, that doesn't have to be a complete ring. It could just be snap hooks, though I like the idea of an entire ring because it provides additional strength and since this is something that will have internal LEDs, it also helps to prevent light from shining through the edge gap (between the bottom "plate" and the upper shell.)