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To you mechanically inclined/engineering types, project help

Bldr_DH

Monkey
Aug 8, 2003
767
0
NO BO CO
I'm hoping some of you monkeys can help give me some ideas for a project I'm working on -- I'm basically making a tiny four-bar linkage that will be used as a hinge. Think of the hinges used on the trunk or hood of some cars.

What I'm getting hung up on is how to make the pivots be both smooth and solid as possible, emphasis on the solid part... every linkage I've ever fudged together has had play like crazy and I want to eliminate it at the pivots as much as I can. The pivots don't need to be free spinning (it's okay if there is some drag), but they need to feel smooth. Nothing has been bought or fabricated yet so there is plenty of leeway with the design.

As it stands, the links have a .125"x.5" cross section. I can maybe bump them up to .25" thick but I'd rather keep them as thin as possible. I was originally thinking about using thrust bearings/bushings since that would give a slightly larger contact area at the pivot to help reduce play. I'm still thinking that may be a good way to go, but I'm open to any ideas. My trouble with the thrust bearings is: I've never actually used them before and am having a tough time imagining how to bolt everything together so the fastener won't back itself out. Maybe some Locite would be sufficient?

The other option would be to make the links thicker and press in a standard bearing.

Thoughts?
 
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Mr Jones

Turbo Monkey
Nov 12, 2007
1,483
0
My trouble with the thrust bearings is: I've never actually used them before and am having a tough time imagining how to bolt everything together so the fastener won't back itself out. Maybe some Locite would be sufficient?


Thoughts?
jambnut or crown nut with cotter pin


Thats all I got so far. Too early in the morning.
 

Bldr_DH

Monkey
Aug 8, 2003
767
0
NO BO CO
Ooh, good thought. Happen to know what these are called? "Pin clip" didn't come up with anything on Google or McMaster

Edit: Found 'em -- retaining clip.
 

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w00dy

In heaven there is no beer
Jun 18, 2004
3,413
30
that's why we drink it here
To take out wobble you either need deep links with a lot of pivot overlap or broad links so the links contact each other on a large surface area. I think you're leaning towards the latter. I'd tighten them against each other with a plastic washer in between. They make teflon sheet, but any kind of nylon would work great.

Edit: http://www.mcmaster.com/#thrust-bearings/=dpb0he

Thrust>Solid>Plastic
 
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Mr Jones

Turbo Monkey
Nov 12, 2007
1,483
0
Ooh, good thought. Happen to know what these are called? "Pin clip" didn't come up with anything on Google or McMaster

Edit: Found 'em -- retaining rings.
I've heard those referred to as 'cir clips'. Not sure of the exact label though.
 

HAB

Chelsea from Seattle
Apr 28, 2007
10,884
1,147
Seattle
If you really want to keep things simple, just use a nylon washer between the links, and then to keep the bolt tight without having to tighten the **** out of it and thus making the pivots suck, just use two nuts and tighten them against each other. Kinda like you'd do on a loose ball bearing hub with the cone and locknut. You'd have to be careful to get the bolts tightened just right so that there isn't play but the pivots still work smoothly, but once you've done that it should be solid.


The parts you're talking about are way too small for thrust bearings to work well.


Edit: sniped by w00dy.
 
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Bldr_DH

Monkey
Aug 8, 2003
767
0
NO BO CO
Awesome, thanks for the tips. I was leaning towards bushings anyway, since they're much lower profile.

McMaster has bowed retaining clips (#98398A120) which I think may do the trick. Has anyone used those before? I'll be turning down my own pins so I can put the groove exactly where I need it. Maybe I can get away with non-bowed ones too...

*Trying to make this thing really low profile and clean, so I'm shying away from the nuts and bolts/cotter pin options.
 
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DirtyMike

Turbo Fluffer
Aug 8, 2005
14,375
947
My own world inside my head
Yeap technical term fo rthose clips is " Oh holy **** were the **** did that go..." clips

I was looking at a trunk today, and the four bar link was exactly what you expect to see aside from it has a cross strut going across from link to link for more support.....

Also use bushings instead of a bearing, large diameter pins, thick wide brackets.


What are you looking to have swinging on a hinge?
 

Bldr_DH

Monkey
Aug 8, 2003
767
0
NO BO CO
It's going to be for a briefcase of sorts. It has a carbon fiber shell, so it won't be seeing any heavy loading at all. I just need the thing to feel solid as a rock. Most of the stiffness will come from the shell itself, but it doesn't hurt to cover all of my bases.

Clip related: As I was popping that one off of my Straitlines to take a picture, the damn thing about took my eye out. Hit me dead center in the forehead.