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

 

[3DDave]

On a similar joint I put a counterbore in the pin ends and then set it up on an arbor and crushed a ball bearing larger than the counterbore to flare each end of the pin into the hole. The ball bearing stays with the arbor. This also ensures the sliding surface is the middle - you might press a self-lubricating sleeve into the middle to avoid wear.

There are also rolled spring pins as well if you wanted to remove and reuse the pin.

 

[TugboatEng]

Are there going to be many links like a chain or just a single joint? If many, riveting or swaging the pin is surely the most economical route. Press fitting can be an option. Use shims during pressing to keep the outer ears from deflecting. If one connection is to be made, set screws or roll pins can work.

 

[bcavender]

Dave,
On your rivet, were you using a standard headed rivet with one head already formed or a straight pin crushed on both ends?

I can visualize both … with the double crush being perfectly flush with the sides on the first go and no secondary operation would be needed to clean up. (A counter sunk rivet would solve half that issue too).

Nice.

The self lube sleeve for the inner is also a great idea! Kudos!

The roll spring is an idea that had not hit me. This would be an interesting option since a basic press would fill the bill … the only question would the ‘spring’ fatigue over time and lose its bite?.

Sounds like the crushed 6061 rivet idea though would be the most reliable in the long run and solve the material corrosion issue too.

Very good!!!
Thank you,
B

Tug,
Your shim idea to prevent yoke deformation is spot on. It’s important to keep the links tight, but it would be easy to create a binding problem without proper care during the rivet install. Good practical advice!
Thanks!
B

 

[3DDave]

I literally crushed both ends as they needed to remain flush. The force is mainly axial pushing material radial so depending on fit it may not squeeze the sides together. Some other swage shape may be better - I happened to have a supply of ball bearings handy.

Get a screw machine shop to make all the pins you need. They make more than just screws.

 

[SWComposites]

Is this a safety critical part?
What is the level of load?
Pin/hole diameter?
Need to be replaceable? Or removable?
Presumably you don’t want an aluminum pin to avoid galling.

 

[MintJulep]

This is a common application for semi-tubular rivets.

If you want to avoid tooling, try a push nut

https://www.advancecomponents.com/fasteners/palnut-push-ons/

 

[bcavender]

SWC,
1. Not safety critical, but prefer to stick w avoiding downtime/repairs.
2. Load: 200 lbs tension peak, typical 50-80.
3. Hole: 0.5”. Pin: Hole-sleeve-0.015”
4. Permanent pin set
5. Galling: This is above my knowledge level.
Rotation is limited to about 40 degrees and motion would only take place once or twice a day for a very short interval.

I was thinking about a thin, self lube, plastic sleeve inside the middle link hole would eliminate friction sufficiently … then going with a AL6061 rivet to avoid corrosion/galvanic action possibilities. But I am def looking for experienced suggestions here.

 

[bcavender]

Mint,
I will def give these a look towards pricing, corrosion. Never designed with these, but have seen them work.
Thanks!
B

 

[SWComposites]

https://en.wikipedia.org/wiki/Galling

 

[bcavender]

SWC,

Thank you for the galling ref. I see the problem clearly now. I do appreciate that!

This opens a new question about below what load and rotation conditions would a self lube sleeve give good service life as well as what level of more intense conditions would require capitalizing up to ball bearings for good long life design.

It’s clear I need to research sleeve/bushing design and search out their better vendors.

Very helpful and timely !!!

Thank you!

B

 

[Sparweb]

Why not a clevis pin with a cotter key?
Works great for small trailers.
There are aerospace varieties which should tell you there's a reliable way to do this, when done properly.

Is there some need for angular alignment of the two bars?
If not, then roll-pins, bearings or custom-made dowels are overkill.

The parts you want are at Harbour Freight (or McMaster-Carr if you prefer).

 

[S-eng]

There are some good plastic self-lubricating bearings from IGUS I had success with.

 

[bcavender]

Spar,
The clevis pin/cotter is going to be an inexpensive, off the shelf commodity. Had not thought of that.
It will be a little longer on labor, but the material price might offset that. Interesting.
Thanks!
B

S-eng,
I had been checking out the IGUS site and came across their bushing service life calculator.
Fast/Easy. My first test run sold me on their company.

So much better than a pic and price.

B

 

[SwinnyGG]

I personally much prefer oil impregnated bronze to plastic bushings - but if your loading is super low and not constant the creep of a plastic bushing may be a non-issue.

Oil-impregnated bronze bushings are cheap and readily available in standard sizes from MMC.

https://www.mcmaster.com/6391K212/

 

[bcavender]

Swinny,
Good suggestion. Will look into pricing!
Tnx!
B

 

[hendersdc]

A cheap option would be a grooved or knurled pin that is pressed in like these from mcmaster: [URL unfurl="true"]https://www.mcmaster.com/products/pins/dowel-pins~/center-groove-dowel-pins/[/url].

I know they only go up to 3/8" on that page but it gives you an idea of a possibility. You may need to switch your bushings to be located in the two outer holes instead of the center one to make it work though. They are about $1 cheaper than the clevis and cotter pin approach so it depends how many you need and if the cost savings is worth it.

 

[IFRs]

Spring pins? bore the inner or outer parts slightly larger, the spring pin will "stick" to the other ID.

https://www.mcmaster.com/products/spring-pins/slotted-spring-pins-6/

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

https://www.mcmaster.com/products/spring-pins/flat-head-quick-release-pins/

https://www.mcmaster.com/products/spring-pins/coiled-spring-pins-6/

https://www.mcmaster.com/products/spring-pins/vibration-resistant-slotted-spring-pins/

https://www.mcmaster.com/products/spring-pins/heavy-duty-coiled-spring-pins/

`

 

[bcavender]

IFRs,

The spring/roll pin is interesting.

Coming up with the design process is key.
I found Spirol has a good initial overview:

https://www.google.com/search?q=eng...ate=ive&vld=cid:af7d3c79,vid:-5wn5zASt4U,st:0

The coiled spring pin is attractive and they tout the advantage that the design can absorb dynamic loads without damaging the hole. This seems a bit odd to me in that, knowing the dynamic load, the designer can specify both the fastener and holder not to deform the hole at that loading.

The concern that I would have is that how does the designer avoid a fatigue loss of spring tension after X number of loading cycles?

OTOH, it would be interesting to see if the distributed dynamic load absorption over Y numbers of spring pins could replace a separate spring tensioning assembly designed to mitigate some level of shocks

The long term concern being the impact of having tens of thousands of assemblies spread out over the country and having some number of pins working their way out and disabling the entire machine. A pin ‘walking out’ would be as economically equivalent to it failing in shear. In any significant number, it would be a logistics/financial nightmare.

Having no experience with spring/roll pins may make me overly cautious … and I need further info/education in this design process.

Great suggestion!
Appreciate your input!
B

 

[bcavender]

A little study on spring rolls pins was enlightening.

The Spirol 19002 Standard duty, chrome stainless, 1/8” x 1.25” is good for 1400# in double shear at around 20 cents each (1000) … which is easily 3-4X this load.

A smaller hole allows more 6061 meat in the links. A plus.

However, with the roll pin’s edge inside the inner, bushed link, it seems that using a plastic (IGUS) bushing creates the chance of the pin’s edge digging into the plastic, which could create a binding problem?

Possibly moving to a bronze bearing to encompass the hardened stainless roll pin would be a better choice to be pressed into the middle link hole in the aluminum link?

Thoughts?
B