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Interlocking methods for two rotational parts - what is best for my application?

josh623

Plastic
Joined
Feb 26, 2016
Hey guys. I basically have two square bars of steel that I want to use one bolt to attach them to make a pivot point. But when I tighten the bolt I want it to be strong and not slip. What is the best way to accomplish this? I'm considering something like machining these geared type steps into the face of each bar at the contact point (basically a raised integrated 'washer') but is that the best method for this? This would only allow the bars to lock into place at specific angles though...

i-d2vsS6k.png
 
That's certainly a strong and dependable way to do it, but it also depends on the user to ensure mesh when tightened. If that's not an issue then this method is pretty hard to beat for overall no-slip performance. Obviously, you can refine the grip points by increasing the number of teeth. If you need to maintain a certain tooth size you can still cut more teeth, just make the ring bigger (this will also have the effect of reducing leverage on the clamp as a whole, a win-win).
 
WTF is a "rotational" part? Try speaking English ( or at least a real language) if you really want an answer. And congratulations! You have just reinvented the Hirth coupling.
 
That's certainly a strong and dependable way to do it, but it also depends on the user to ensure mesh when tightened. If that's not an issue then this method is pretty hard to beat for overall no-slip performance. Obviously, you can refine the grip points by increasing the number of teeth. If you need to maintain a certain tooth size you can still cut more teeth, just make the ring bigger (this will also have the effect of reducing leverage on the clamp as a whole, a win-win).

Thanks for the input, yes I may make the steps smaller/tighter for more capability/angles.

What kind of loads?

I would say 30 lbs @ 6" from the joint would be ideal

If you need infinite adjustment, you could use a stack of clutch plates until you get enough friction

Not familiar with those... but the bolt that will be running through

WTF is a "rotational" part? Try speaking English ( or at least a real language) if you really want an answer. And congratulations! You have just reinvented the Hirth coupling.

Sorry I'm struggling with the terminology. But you actually answered one of my questions, I wasn't sure what this joint was referred to as and now I know it's a Hirth coupling! That is very helpful, thank you. So I guess what I'm asking is - is there any alternatives to a Hirth joint that would still be relatively strong yet without having the 'steps' that a Hirth joint does...?

All depends on what load the pivot point sees and dimensions
You gave us no indication so far

peter

Sorry, load is above... the square bar stock will be 1-2" and the joint will have a 1/2-13 bolt running through it.
 
For 30lbs at 6" all you need is flat mating surfaces and an adequately sized and torqued bolt. I'd use at least a 3/8" bolt which provides way more than enough clamping for what you describe. You're not looking at anything more demanding than a mid-size flat-screen mount!
 
For 30lbs at 6" all you need is flat mating surfaces and an adequately sized and torqued bolt. I'd use at least a 3/8" bolt which provides way more than enough clamping for what you describe. You're not looking at anything more demanding than a mid-size flat-screen mount!

Yep, what Gordon said. Just bolt them together and you'll be good. Get the interfaces flat so you don't have any point loads. Placing some gasket material in between (thick paper would work well).

If you are using tube then create some inserts right at the joint so the tubes don't collapse when tightened.
 
Even better than flat, you can machine .001-.002" away from the center of the bar faces to make sure that primary contact is around the perimeter, that should be more than enough for the load you describe.

Single layer of brown paper to smooth out inconsistencies would also work.
 
I would say 30 lbs @ 6" from the joint would be ideal

Sorry, load is above... the square bar stock will be 1-2" and the joint will have a 1/2-13 bolt running through it.

What is the purpose?

What is the shock and vibration environment? How dirty is the environment? Corrosive?

Are the users skilled enough to be trusted alone with a wrench?

If the joint does slip or even let go, what bad things happen? Any funerals?
 
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So we are trying to improve the mount for a bicycle seat.

The Hirth coupling is probably the best if you are trying to keep it simple and compatible with existing mounting points. But unless the two sides of the Hirth coupling are firmly attached to the mount and the seat, then they can simply rotate on the back side of the Hirth washers. It is best to incorporate those Hirth coupling features into that mount and seat themselves instead of adding them.

An alternative would be spring lock washers:

McMaster-Carr

These should provide a positive lock while allowing infinite adjustment.
 
Hopefully the OP can recognize there are a ton of variables needed to provide a good answer. Please provide these details and we can help much faster. Just describe exactly how this will be used.
 
I’ve been enjoying the ideas in this thread. I had a similar application in my driving-simulator frame where the shifter-mount arm cantilevers off a vertical post. The arm is slotted, with a sleeve on the clamping bolt to stop it from collapsing, but there still wasn’t enough torque resistance in the joint. Making some large washers to put the load through the aluminum square-tubing sidewalls helped considerably. I tried a disc of adhesive sandpaper in the joint but the adhesive allowed too much shear motion. Maybe cork would have been better. Or, it occurs to me now, a piece of drywall sandpaper (double-sided abrasive, noncompliant).

The interleaved plates I have seen in an angle-adjustable drafting table my neighbor was messing with. They somehow broke that aspect and I helped make a new pivot mechanism but it just used a bolt through a circular arc to clamp rotation. The friction pad seems neat.
 








 
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