Help making small pin joints between plastic rods

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  #1  
Old 03-02-13, 12:42 PM
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Help making small pin joints between plastic rods

Hey all, very nice forum! Lots of stuff here.

I'm looking for some advice on something. I'm making a tiny little model of a basic skeleton from scratch. I want to make it out of small plastic rods (like 5mm diameter for a leg). I'm trying to figure out the best way to make elbow/knee joints. Not finding anything ready-made of that size. The joints need to move fluidly (don't want it to be strong enough to support its weight, should just be very loose and moveable).

I was thinking of maybe hand-machining them with a Dremel tool. I'd sand away half of the material at the joint area (so the end of the rod would be a half-cylinder rather than a full one), then putting the rods together (flat face touching), drilling a hold through it, and puting some kind of pin through it.

Is this a good approach, or do you guys know a much simpler one? If this is the right way to go, what sort of materials do I need to get for the "pin" part? Presumably, it'd have to be something I can saw to be just the right length (not stick out too much at the joint, but leave just enough wiggle room for the joint to be moving).

Thanks!
 
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Old 03-02-13, 12:59 PM
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Welcome to the forums !

The hand machining idea is a good one. I would use small nuts and bolts. You can use an online search to find small hardware or try a local hardware store or even Radio Shack.
 
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Old 03-02-13, 01:03 PM
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What would be wrong with using something soft like thin copper wire, and just bending a sharp L on each end to keep it from sliding out? Would be simple...
 
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Old 03-02-13, 03:07 PM
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I think you could use a rivot. Drill your holes as you would for any rivot connection, when you are ready to fasten, add a filler (putty knife or something) and set the rivot. Remove the filler and you will have a strong, loose joint.
 
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Old 03-02-13, 05:17 PM
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What is a rivot? Do you mean a rivet?
 
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Old 03-02-13, 05:47 PM
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Thanks Furd, you are obviously not from the south...but the lack of correct spelling didn't indicate if you agree with my possible solution to the OP's request for help with his need for a solution to his/her situation.
 
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Old 03-02-13, 06:27 PM
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Nope, not from the south. Using a rivet might be acceptable as long as the rivet material is such that the plain end can be upset without damaging the plastic material. Maybe even make rivets out of plastic and use a hot knife to upset the ends.
 
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Old 03-03-13, 05:35 PM
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Thanks for all the replies, guys! Some quick clarifications:

PJmax: Seems fairly straight-forward. How does one use nuts and bolts, keeping them loose enough not to force the components together, but at the same time, guaranteeing the nut doesn't come off over time, with all the random rotating/movement that may happen?


XSleeper: Unless I misunderstood what you meant, making the joint out of wire would make it too rigid. I want it to flop around. Like, if I grab one stick of the elbow and wave it around, the other stick should move freely, like a pendulum. Imagine nunchucks without a chain. Except it's an elbow joint, so only bends in one plain. I guess, "imagine a person's elbow flopping around" would have been easier.

czizzi: Hmm yes a rivet (maybe a pop rivet?) with something between the pieces while applying, sounds like it could do the trick. Is the act of setting a rivet violent enough that it risks destroying the plastic in some way? I'll look into what's available. Pop rivets look like they're really long, but maybe I can find a tiny one of the right size or something. Thanks for the tip!

Furd: haha thanks for the correct spelling. I don't know the names of a lot of common DIY-y things. Like, I know what scissors are, but I don't know the name of the pin holding the pieces together (is that also a rivet?) So correct spelling does make it easier to search for stuff. Aaaand looks like you also answered some of the follow up questions I had above (I'm just writing these as I read responses).


cheers!
 
  #9  
Old 03-03-13, 06:53 PM
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I'm picturing a working joint with a hole drilled through the 2 parts making up the "knee"... and the wire bent downward on each side of the moving joint (shaped like a ]....) so that it keeps both parts together but is still loose and can't fall out. The downward bent sides of the wire would be left sticking out the sides so maybe that isn't the clean look you are after, I dunno.
 
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Old 03-05-13, 10:46 PM
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Aah ok I see that makes more sense. Misunderstood the first time.

Yeah, the sharp bits sticking out are somewhat undesirable, and I think a rivet-like solution would be a bit more solid.

Thanks for all the input!
 
  #11  
Old 03-25-13, 12:18 PM
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threaded rivets

Acutally I don't have a clue what they are called. Corrections accepted here.
I've found many small toys and other objectes held together with what appeared to be a rivet with a perfect head on both ends. Being a normal male I've taken some apart.

What I found was one head was the end of a hollow shaft with inside threads and the other was the end of a solid shaft with outside threads. The solid, outside threaded shaft could be cut short so that it "bottoms out" at the correct length to leave some space in the joint. If I could draw I would attach a sketch. Anyway these must come if many various sizes because I've seen them in many various sizes.

Again no clue what their name is so this may very well have been a futile effort on my part.
 
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Old 03-25-13, 08:01 PM
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I know exactly what you are talking about. I have some larger ones here.
Big orange has them in the hardware aisle in those pullout cardboard drawers.
I'm not sure how small the ones are they stock.

Something along the lines:
Anchor nuts
Rivet nuts
Hollow nuts
 
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