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Shoulder Bolts in a Bolted Joint

Shoulder Bolts in a Bolted Joint

Shoulder Bolts in a Bolted Joint

The shoulder portion of the shoulder bolt could be used as an axle or journal to provide rotational degree of freedom for a part in the joint using shoulder bolts.
When a joint has three members, the first member rests on shoulder of the bolt which acts as an axle for the member, the second member is attached to the third member which has a tap hole where the threaded portion of the bolt is engaged.
When the thread engagement of the bolt is inside the bolt hole, not on the edge of the hole, and the shoulder face of the bolt comes into contact inside the hole having a step provided for the purpose.
In the joint described above, is this the interface where the clamping force/interface pressure acts?
When the bolt thread engagement is below the joint members interface and shoulder of the bolt comes into contact inside the hole and there is an interface inside the hole not at the members outer surfaces, and members has a clearance between them, the clamping force could not be reacted at the members outer surfaces interface as this happens in a bolted joint with regular bolts.
When there is a gap between the members bolted together with shoulder bolts, in this case, is the clamping loads being reacted where the bolt shoulder face has contact with the stepped area inside the tapped hole of the other member.
Thanks for your education, sharing the knowledge of the mechanics of the bolted joints using shoulder bolts.

RE: Shoulder Bolts in a Bolted Joint

A sketch would be more than helpful here.

Also, I recommend Bickford's books if you want to dive into the finesses of bolted joints.
I did 20+ yrs ago, and still carry (most of) the basics with me.

RE: Shoulder Bolts in a Bolted Joint

From the description I believe you are on the correct path. Shoulder bolts are analyzed and react just like regular bolts, the main difference being that the portion of the bolt above the shoulder isn't subject to tension/stretch so from a bolted-joint perspective you're only really concerned with the lower portion. Be sure and take a close look at under-head (under-shoulder really) contact stresses as many shoulders have a smaller area than same-thread hex bolts. I also like to make a point of calling out their use to the larger team so technical writers, customer service, etc know to warn techs not to overtighten them, some folks see a big hex and ass-u-me a big thread/high torque.

RE: Shoulder Bolts in a Bolted Joint

Be very careful with lateral loads on shoulder bolts, the threads are small and unless the bolt is short it will not like the bending. They are meant for axial loads.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Shoulder Bolts in a Bolted Joint


Definitely, you need to post a sketch. I am not able to visualise your description.

If you have two or three parts rotating about the common axis of your shoulder screw, do your tolerance stacks. You might be surprised at how accurate plate thicknesses aren't. If your two or three rotating pieces are thick, analyse the bending moment at the base of your screw. You might be surprised.

Why would your tapped hole be inside a pocket? (???) Are you trying to control the clamping thickness? Again, do your tolerance stacks.


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