Torque and grease

[Lewis Moon]

I always use a torque wrench whenever possible and specs are published. What I've always wondered is: with or without grease?

I sometimes wonder if some of the cracked face plates or snapped bolts were because a bolt was greased that should have been dry.

[El Chaba]

Grease-or antiseize- should be used save for the rare instances where dry is specified...(such as Campagnolo does for square taper cranks)....

[Mark McM]

I can't think of a single instance where threads aren't to be lubricated (or treated with some other thread compound) when torqued.

In the previous thread on the Deda faceplate, the Deda instructions specifically say:

Grease the faceplate bolts if needed (our bolts are pre-greased with esalock) and thread them by hand (just a few turns), being careful that surfaces between stem, faceplate and handlebar are not contaminated with grease.
Tighten the bolts so that the upper and lower clamping slots represent the same width. Then, using a torque wrench, tighten the bolts alternately in a cross pattern, turning ½ turn at a time.
With the 4-bolt faceplates, tighten the bolts alternately in a 1-2-3-4 cross pattern, until a torque of 4 N•m is reached.

So, it's pretty clear in this case.

As for Campagnolo square taper spindles, they are clear that the bolts should be greased, only the taper flats should be dry. (Although in this case, they are wrong about the taper flats, buts that's a different discussion.)

[berserk87]

Maybe I can't think straight today, but I will ask anyway - would the application of grease make a difference? Isn't 5nm the same torque, whether greased or not? Grease may make the threads turn easier, but isn't the net measurement the same whether greased or not? Please help me out on this. I cannot brain, as I have the dumb today.

[jtakeda]

Originally Posted by berserk87

Maybe I can't think straight today, but I will ask anyway - would the application of grease make a difference? Isn't 5nm the same torque, whether greased or not? Grease may make the threads turn easier, but isn't the net measurement the same whether greased or not? Please help me out on this. I cannot brain, as I have the dumb today.

I was going to say the same thing.

But I always grease all metal on metal unless specified.

[Mark McM]

Originally Posted by berserk87

Maybe I can't think straight today, but I will ask anyway - would the application of grease make a difference? Isn't 5nm the same torque, whether greased or not? Grease may make the threads turn easier, but isn't the net measurement the same whether greased or not? Please help me out on this. I cannot brain, as I have the dumb today.

This would be true - if the end product we are interested in is the torque on the bolt. But it isn't - what we're intested in is the clamping force created by the bolt (in the thread on the Deda faceplate, it was the face plate that broke, not the bolt).

The bolt converts the applied torque to a clamping force via rotating on the threads, which form a helical ramp and which pulls the bolt to a higher clamping force as it screws into the threads. The further the bolt screws into the threads, the higher the clamping force. The amount of torque required to screw the bolt the desired distance up the threads will depend on several factors including the friction on the threads - the higher the friction, the higher the torque required to turn the bolt to desired amount. So, the presence of a lubricant will reduce the torque required to achieve the desired clamping force.

Why not specify the bolt torque with dry threads, and remove the grease from the equation? Because dry friction varies quite a bit, whereas lubricated friction is more consistant. Therefore specifying the torque for a lubricated bolt will achieve a much more consistent clamping force than torquing with a dry bolt.

[berserk87]

Originally Posted by Mark McM

This would be true - if the end product we are interested in is the torque on the bolt. But it isn't - what we're intested in is the clamping force created by the bolt (in the thread on the Deda faceplate, it was the face plate that broke, not the bolt).

The bolt converts the applied torque to a clamping force via rotating on the threads, which form a helical ramp and which pulls the bolt to a higher clamping force as it screws into the threads. The further the bolt screws into the threads, the higher the clamping force. The amount of torque required to screw the bolt the desired distance up the threads will depend on several factors including the friction on the threads - the higher the friction, the higher the torque required to turn the bolt to desired amount. So, the presence of a lubricant will reduce the torque required to achieve the desired clamping force.

Why not specify the bolt torque with dry threads, and remove the grease from the equation? Because dry friction varies quite a bit, whereas lubricated friction is more consistant. Therefore specifying the torque for a lubricated bolt will achieve a much more consistent clamping force than torquing with a dry bolt.

Thanks for taking the time to reply.

Man, I am not on my game today with thinking in detail. I need a nap. It still is not hitting home. I'll revisit this later after I wake up.