Cut Tread vs Rolled Treads

[Stache]

I have read the weakest area of any mechanical fastener is the minor diameter of the threads. Since the thread dimensions of a cut thread and rolled thread fastener are identical, I would like to know if there is difference in strength between the two.

I have seen a lot or cut threads fail in structures and some manufactures call out both type of fasteners in the same part. An example is having two cut threads fasteners and two with rolled threads fasteners in a elevator fitting in accordance with the IPM.

Is there a reason to be concerned?

Stache

 

[CoryPad]

The difference in strength between cut and rolled threads usually is seen in fatigue. Rolled threads are better due to less sharp corners, as well as residual stresses (if done after heat treatment).

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[yates]

'the weakest area of any mechanical fastener is the minor diameter of the thread' is a reasonable assumption when considering a constant load along the bolt axis. In real life this rarely happens and you will find that there is often some degree of oblique loading, which may introduce bending in the head and cause the bolt head to snap off, or cyclic loading which, as Cory points out, is better contained by a rolled thread than a cut thread. While not resulting directly from the threadroll operation, a rolled thread bolt will often have had underhead fillet roll, which introduces compressive stress into the underhead radius and provides better resistance to head snap off.

 

[rb1957]

rolling the thread will also produce a much better grain direction in the thread