[monte55]

I have a project where I am using 1/4" x 28 tpi black alloy socket head cap screws with a hardness of C38-42. I would like to have a strong bolt in this application. When I look at a grade 8 bolt to replace it, it says the core hardness is RC 33-39. Would it be worth the change. These bolts will have to endure shear stress the most......................Nick

[jmkasunich]

Socket head cap screws (unless they are counterfeits from China) are at least as strong as grade 8 bolts, maybe stronger. There is some info here: http://home.jtan.com/~joe/KIAT/kiat_2.htm

If the load is mostly shear, one thing you can do to improve the strength is make sure there are no threads in the shear plane. That may or may not be possible - depends on the length of the screw, how much of it is threaded, and how close a fit you can get between the unthreaded shank and the hole.

If you _really_ need maximum shear strength, design the parts to accept a couple nice sized dowel pins in reamed holes. The pins will take the shear, and the screws will just hold things together.

Bolted joint design can be a science in itself - and I don't know how much latitude you have. But my gut feeling is that it will be hard to top a good quality SHCS.

John

[CalG]

Unbreako makes really good SHCS.

Or choose NAS specified fasteners from the aviation industry. They are good!

CalG

[monte55]

Socket head cap screws (unless they are counterfeits from China) are at least as strong as grade 8 bolts, maybe stronger. There is some info here: http://home.jtan.com/~joe/KIAT/kiat_2.htm

If the load is mostly shear, one thing you can do to improve the strength is make sure there are no threads in the shear plane. That may or may not be possible - depends on the length of the screw, how much of it is threaded, and how close a fit you can get between the unthreaded shank and the hole.

If you _really_ need maximum shear strength, design the parts to accept a couple nice sized dowel pins in reamed holes. The pins will take the shear, and the screws will just hold things together.

Bolted joint design can be a science in itself - and I don't know how much latitude you have. But my gut feeling is that it will be hard to top a good quality SHCS.

John

Thanks...........that is a good link for info..........................Nick