Beam-indicating Torque Wrench Technique Question By ducked (Read 430 times)

[ducked]

Just used one on the gf's scooter head bolts, and realised I wasn't exactly sure how! Embarassing



(I've used one before but a long time ago, and maybe I didn't think of this before)



My uncertainty is with the interpretation of the standard "tighten nut until the specified torque is reached" instruction.



Just now, when I did that, the nut was still moving.



Should I stop at that point (as the standard instruction seems to imply), or hold the torque at that level until rotation stops?



The former seems likely to vary, depending on how fast you tighten the nut.



The latter seems likely to be more reproducible, but also likely to get the nut a lot tighter.



This is using a beam-deflection wrench.



I suppose, with the click-type, (which I don't have) you don't have the option of holding at the set torque value, but the rate at which you reach it must still influence the final tightness of the nut?

[Alleyoop]

Yes on a beam type as you do a STEADY PULL and it reachs the desired torque stops applying force.
Alleyoop

[Bashan]

It was still moving? Like loose? What is the torque on that bolt? It should have been pretty tight and not moving. Is that the kind of torque wrench with the pointer on a scale? Those are not accurate at lower levels like 40 to 60. They work OK at higher levels. Get the click type for scooters even if you have to borrow one from auto weinie. They work well on the lower settings you need on some bolts, even down to ten. Some of the bolts on a scooter are like 7, I just wank them tight with my 1/4" drive. Anyway, in answer to your question, that doesn't sound right to me, I'd get another wrench.

[ducked]

As far as I can work out, my perceived problem still applies with the click-type wrench, its just less obvious.

If (say) I'm aiming at 30 ft-lbs and I hold it at 29 until it stops turning, then go to 30 and stop, (or click) its going to be tighter than if I go to 30 as fast as I can.


Same applies to the click-type. If the bolt is moving, there seems to be scope for a lot of variation due to technique.


More I think on it, the dodgier it seems.

[ducked]

I suppose if you increase the torque gradually, so movement has time to happen, and you approach the "click-point" slowly, that should reduce the variability.



The distinction between reaching, and holding at, the specified torque, while it is a real one, isn't one that's easy to make with a beam-indicating wrench, due to its wider range of reading precision, so it probably isn't worth worrying about.



Friction is probably a larger variable, and I'm generally working with oiled or greased bolts, (while dry is usually specified/assumed) so obsessing over fine points of torquenique probably doesn't make much sense.

I don't like stripped threads, but I don't like seized/stuck threads either.

This thread

www.thumpertalk.com/topic/426292-greasing-all-bolts/

includes a suggestion to torque down dry to 1/3 of spec, and then record the angular movement required to reach final spec. You then repeat that movement with a lubed fastner, so it reaches the same position (and hence tension) though the torque, if you measured it, would be less due to the lube.

The assumption is that at the 1/3 starting/reference point the torque isn't significantly affected by the lube.


I dunno about that, but I'd think if you counted total turns from the start, that assumption wouldn't need to be valid anyway. Think I'll do that in future.