Grease a square taper spindle, yay or nay?

[GuyBoden]

All I know it that lubrication affects or reduces torque, so you could under tighten. That's
if you use a torque wrench or your guesstimator might be under tightening.

"Dry bolt torque is approximately 30% higher - or 628 lbf ft. If the bolt is lubricated with SAE 30 oil - the torque compared to a dry bolt is reduced with approximately 40%."

 

[Ajax Bay]

I advocate greasing the crank bolt @GuyBoden , though the toque needed is 'well tight' on my meter.
This (ungreased) thread is about whether to grease the tapered end of the spindle.

 

[figbat]

All I know it that lubrication affects or reduces torque, so you could under tighten. That's
if you use a torque wrench or your guesstimator might be under tightening.

"Dry bolt torque is approximately 30% higher - or 628 lbf ft. If the bolt is lubricated with SAE 30 oil - the torque compared to a dry bolt is reduced with approximately 40%."

I think the opposite is true. If you lubricate a nut/bolt and then apply a set tightening torque to it, the bolt will be under more tension than an unlubricated one. During a training session many many years ago from a ship engine builder they hammered home the requirement to know if a torque value for doing up a nut is dry or lubricated. If you have a dry torque value but use it to do up a lubricated nut, you run the risk of snapping the bolt or stud.

On a related musing, the cylinder head nuts on large ship engines are done up hand tight.

 

[GuyBoden]

I think the opposite is true. If you lubricate a nut/bolt and then apply a set tightening torque to it, the bolt will be under more tension than an unlubricated one. During a training session many many years ago from a ship engine builder they hammered home the requirement to know if a torque value for doing up a nut is dry or lubricated. If you have a dry torque value but use it to do up a lubricated nut, you run the risk of snapping the bolt or stud.

On a related musing, the cylinder head nuts on large ship engines are done up hand tight.

Yes, that's correct, the torque needs to be less when lubricated, then you have to guesstimate a torque setting and probably under tighten.

Or use the following easy formula.

Example - Reduction of Torque when Bolt is Lubricated​

The maximum tightening torque for a slightly lubricated 1" Grade 5 coarse bolt is 483 lbf ft. Dry bolt torque is approximately 30% higher - or 628 lbf ft.

Tdry = (483 lbf ft) (1 + (30%) / (100%)) = 628 lbf ft

If the bolt is lubricated with SAE 30 oil - the torque compared to a dry bolt is reduced with approximately 40%.

TSAE30 = (628 lbf ft) (1 - (40%) / (100%)) = 377 lbf ft

Note that if torque specified for a dry or slightly oiled bolt torque is applied to a lubricated bolt - the bolt may overload and break.

https://www.engineeringtoolbox.com/torque-lubrication-effects-d_1693.html

 

[midlife]

The bolts/ screws I attach things to dental implants are lubricated, stops the bolt from juddering when getting up to torque.