Pulley bolted connection torque 1

[Arrow22]

Hello, I could use a little help with a calculation that I've been struggling with.

I wish to mount a pulley to the end of a 20mm shaft whereby a M8 cap screw will secure it, there won't be a keyway or any other method of preventing the pulley from slipping, only the friction from the contact of the end faces as this will be a slip fit onto the shaft.

So this is where I need a little help, I want to calculate the torque required to make the joint fail so the pulley slips on the shaft. The pulley won't actually be under massive load but I'd like to be certain it's not going to fail.

Here's a few pictures of it.

Cheers, Tom

Sorry for large images.

 

[MintJulep]

Roger that.

 

[SnTMan]

How bout an interference(shrink or drive) fit?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Jboggs]

Again - make the shaft stationary and mount the pulley on a bearing. Solved.

 

[jlnsol]

Hello Tom,

Bolt tables say that an M8 steel 8.8 class bolt is tensioned at 90% of its minium yield strength when 24,6 Nm torque is applied.
At that torque the bolt tension will be 18,6 kN.
These values are valid for a thread friction coëfficiënt of 0,12 which means oiled.
I would suggest that you use a loctite bolt locking liquid to secure the bolt to the shaft. That will make the 0,12 value applicable when fastening the bolt since the loctite will act as liquid film.
So i.e. 12,3 Nm bolt fastening torque gives 9,3 kN bolt tension. My best guess here.

Further:
ds = shaftdiameter
dbh = bolt head diameter
dwh = washer hole diameter
dpbh = pulley bolt hole diameter
fs = static friction coëfficiënt between steel parts greasefree and clean is in the range 0,5 - 0,8, so take you’re figure here ;-)
Fb = bolt tension you will apply

Then:
M pulley fail = Fb x ( (ds+dpbh)/4 + (dbh+dwh)/4) x fs

Why the + sign? Because friction will occur at two surfaces together which are at the point to start slipping over each other: the bolt head/washer face and at the pulley/shaft face.
Why the /4? Because we need the mean radius of the contact surface.

 

[Arrow22]

Thanks jlnsol that answers my question perfectly