Need a practical fastener reccomendation 2

[bcavender]

I have two simple links that I need to couple. The links nest together tightly plus the angle of rotation of the links is small and any rotation is occasional/very slow like you would find in a hinge. The major static force on the 12mm pin will be approximately 200 pounds in linear tension (first cut thinking).

There are two goals for the fastener:

1. Since axial forces driving the pin out are minimal, a standard bolt/nut is a bit of mechanical overkill, leaves projections on both sides that are unwanted and requires more assembly time than desirable.
2. The links are 6061 aluminum and the atmosphere has exposure to occasional salt moisture and vapor. So fastener corrosion has to be precluded by the material chosen.

A thin-head, grooved pin with an eClip was the first to come to mind. While this method is a solid solution and better than a bolt/lock nut, I am wondering if anyone has ever seen a pin with with some nature of expanded end that would compress during insertion, then open on the other side to 'reliably' lock itself in place with one insertion motion to drive fastener cost and labor to a minimum?
(Or maybe some form of rivet forming design that also did not require a second part to be purchased/handled ... and had the added advantage over an eClip or push clip that some random debris could pop it off.)

All comments, suggestions and especially even better ideas are most welcome!

Best regards,
B

 

[IFRs]

This one has a toggle that locks:

https://www.mcmaster.com/products/lock-pins/toggle-lock-clevis-pins-6/

There are others with cotterpins, etc.
I'm a fan of clevis pins with a cotterpin, these cotterpins stay in very well:

https://www.mcmaster.com/products/cotter-pins/locking-cotter-pins/

 

[SwinnyGG]

I'd recommend against a roll pin for a joint that is going to see rotation. Not really the right application. It's going to create debris every time it moves, and eventually one of more of the bores is going to open up. This is likely to happen very quickly in an aluminum part.

Bronze bushings are very precise, perfect for one of the locking pins listed by IFRs above, a shoulder bolt, or a permanent rivet as discussed earlier in the thread.

IMO the best solution proposed in this thread so far is the center groove dowel. Gives you one step installation, needs no external feature to stay in place, is removable later for service or whatever, and is precise enough that you can get a good running fit on the bushings which would run in the areas outside the groove, so it won't generate a lot of wear over time.. In your shoes, this is the direction I'd probably go. McMaster only has them up to 3/8", but the breaking strength in shear of a 3/8" dowel is 10,000 lbs or more. Way more than you need in any case.

If you center section is 1/2" wide and the narrow sections on each end are 1/4", you can straight up just buy the 3/8" x 1" center grooved dowel from McMaster along with two 3/8" x 1/4" bronze bushings for the outer bores and be done.

Driv-lok makes them off the shelf in more sizes than McMaster carries.

https://www.driv-lok.com/wp-content/uploads/2012/02/dime-4.jpg

 

[bcavender]

Swinny,

Thanks for your advice. I feel we are getting right down on a solid solution.

I had two reservations related to the spring fatigue as well as the gouging that could come from the edge of the roll. The solid groove dowel makes those moot.

In thinking about failure modes, the center groove moves the rotation to the outside links. I have the concern that over lots of units, invariably one of the bronze bearings will work itself out the side.
What about the idea of having the pin interference fit on the outside links so a single bronze bearing can be fully captive between them? (Plus one bushing install is faster than two.)

I really like the interference fit over a rivet for the install advantages. (I've just not seen "outer" groove pins ... so that might just be wishful thinking on my part.)

My primary concern on rivets is that variability by the riveter could introduce as many or more failures as a bushing wiggling out over time. Then again, possibly I am overly concerned about that due to lack of experience. This isn't a life critical project, but I view it as a quality/long term profit critical project.

Thank you!
B

 

[SwinnyGG]

I would design this assembly so that the bronze bushings are a light press fit.

The order of operations you would want to follow is: press in bronze bushing on one side of the outer link only. Assemble links and press in center cut dowel from the side of the outer link which does not have a bushing installed. You leave this bushing out so that the center groove dowel doesn't score the bushing on its way through. Once that's done, press in the other bushing around the end of the dowel and inside the bore of the outer link.

Alternatively, you could use flanged bushings, which would not need to be press fit since the flange being inside the joint retains the bushing, ie:

https://www.mcmaster.com/products/f...-sleeve-bearings-7/?s=bronze+flanged+bearings

if the flange is toward the inside, it gives you two benefits; the bushing cannot possibly come out, because the flange is on the inside, and also the flange provides lower friction between the parallel faces of the two links. Basically a rotary and thrust bearing in a single part.

Disadvantage of these would be potential scoring of the bushing when the center groove dowel is pressed in, because the groove has to pass through the bushing on it's way home.