What torque settings for accessory screws.

As a newish teacher I am trying to get students to fix things with the correct amount of torque.

Tightening brass screws like they are wheel nuts does not give materials much of a lifespan.

So I bought a couple of torque screwdrivers, so they can quickly get a feel for how tight things should be.

However now I look at data sheets I can't seem to find Torque info for anything smaller than a a miniature circuit breaker.

The data sheets now often include other everyday information like Altitude.

Does anyone have some guidance for smaller brass screw torques, or know of a manufacturer that publishes such data?

Parents
  • For small fixing screws the relationship between torque, and what you are really trying to achieve, a given degree of extension (stretch) or compression of the core of the bolt is very variable as the thread friction dominates over the 'worm drive' action of the thread which after all is just the problem of pushing things up a ramp, but  wrapped around a stick.

    To illustrate this by example  a simple bench top demo can be done to the students to show that a light smear of grease on an M4 mild steel bolt can almost halve the torque required to reach the head shearing tension - or less destructively and more pertinant to terminals, to graunch right though a 1mm wire core..

    For terminals things are complicated by the fact the yield element is the wire being clamped, not the screw body itself.


    Very few makers are keen to publish figures for this reason, and a blind adherence to a fixed torque can lead to problems.
    A starting point for steel in M3 and up here but for brass I'd start by halving everything. You may expect it to scale with UTS of the material but below about M10 threads  it generally does not.

    Mike.

Reply
  • For small fixing screws the relationship between torque, and what you are really trying to achieve, a given degree of extension (stretch) or compression of the core of the bolt is very variable as the thread friction dominates over the 'worm drive' action of the thread which after all is just the problem of pushing things up a ramp, but  wrapped around a stick.

    To illustrate this by example  a simple bench top demo can be done to the students to show that a light smear of grease on an M4 mild steel bolt can almost halve the torque required to reach the head shearing tension - or less destructively and more pertinant to terminals, to graunch right though a 1mm wire core..

    For terminals things are complicated by the fact the yield element is the wire being clamped, not the screw body itself.


    Very few makers are keen to publish figures for this reason, and a blind adherence to a fixed torque can lead to problems.
    A starting point for steel in M3 and up here but for brass I'd start by halving everything. You may expect it to scale with UTS of the material but below about M10 threads  it generally does not.

    Mike.

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