What's the strongest .....

Lizooki

Lizooki

Samurai Frogger
Joined
Mar 21, 2005
Location
Stokes Co. NC
....bolt I can get for this application?

shoulderbolt.jpg

Roughly a 3/8 or so shoulder diameter.
The stress it going to be at the red arrow. (shoulder/bolt junction)
Needs to support 500-600 lbs.
BUT there will be 3 bolts, all in shear. bolted to a "hub".
 

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    shoulderbolt.jpg
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Cap screws are all Grade 8 I believe, but your application really doesn't fit what the bolt was designed for. If the shoulder is 3/8 your threads will be 5/16. Shear at that point would be concerning. There already is a high stress point just from manufacturing. It would be better if you can sink the shoulder into the threaded material with a bored hole of 3/8 so the shear is on the shoulder and not the transition.
 
That stress riser is going to be your down fall. I have snapped a BUNCH of these shoulder bolts when used in the wrong application. There is nothing resembling a radius at that shoulder / thread transition.

If you are stuck on that bolt, I would blend a radius into that existing step.

You could put a sleeve into the parts to aid with alignment and eliminate the shoulder bolt. You could step the thread dia. Up to use a regular shoulder bolt, or you could use a round thread adapter and studs/bolts on the hub side.
 
shelby27604 said:
You could put a sleeve into the parts to aid with alignment and eliminate the shoulder bolt.
Click to expand...

I had that thought also.
Probably would work better since it's going through wood.
Bronze/steel bushing with a regular bolt.
 
Lizooki said:
I had that thought also.
Probably would work better since it's going through wood.
Bronze/steel bushing with a regular bolt.
Click to expand...
With wood, that is definitely a better option, it will keep the shoulder bolt from wallowing out the hole under load. McMaster will be your friend here, you should be able to size a sleeve and a stock shoulder bolt to get a good interference fit with the wood and a clearance fit on an off the shelf bolt.

Depending on the wood, you could also source a hex union and press it into the piece.
 
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Weld it.
 
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Direct link to mcmaster's shoulder bolt selection. The product pages list the ratings.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.
www.mcmaster.com www.mcmaster.com
 
justjeepin86 said:
I'm honestly curious what you are doing that would require a shoulder bolt in wood that you would have a concern about the bolt strength.
Click to expand...

Folding chairs/stools.
Definitely want overkill on the weight rating (fatboy proof).
 
If it is moving parts, then definitely put a sleeve and a bolt with an unthreaded portion riding in the sleeve. This sets the joint up like a bearing and race and distributes the load over the wood fibers.
Overkill would be to use set of flanged, brass bushings to help keep the joint lubricated and to better distribute the clamp force. I hate to use slip washers....toss slim nyloks on there and be done.
 
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