Jam Set Screws

Hi simektp,

I would say that after tightening the main grub screw the "jam" one is the one that comes in behind it to lock the main one in place.

Best regards,

John

Wherever you put it, a jam screw will be the last screw you tighten.

After, no other way.

Which one is the chicken and which one is the egg?

Most times the jam set screw is used behind a previously set screw to either maintain a specified position or lock down a screw or bolt that is under stresses that may loosen it in normal function. However I also use a set screw as a jam when I am using a bolt as a retainer for a moving plate such as an ejector retainer plate in an injection mold. So in that application the set screw in inserted first and the bolt tightened down onto it to hold a position. Admittedly not the common usage but it works very well.

Thank you very much.

I think it calls for more detailed discussion to have better clarity on this topic.

In these pairs, nut and lock-nut or screw and jam-screw, the later is shorter than the former, why?

While tightening do they need same torque or different?

I got my answer. It's not a big deal anymore. Thank you.

Yeah, just leave us hanging! :)

Yes, but how do you know it's right?

It is big deal, I believe.

While tightening the jam-screw, how much torque needs to be applied?

Same torque as in the first set screw or more?

If same torque, then they together would act like a long screw of length equal to set screw plus jam screw. We could have selected one long screw instead a set screw and a jam screw, right?

So, jam screw has to be tightened with more torque, right? How much more?

I got to use a 1920's or so heavy mortiser capable of very large stile and rail designer doors that had the jam set screws, and at that machine you tended to be thankful for them with the way those heavy knives digging in would throw back vibration into everything in the vicinity. There's a huge amount of force on some tools.