Pulley bolted connection torque
Pulley bolted connection torque
(OP)
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.



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.








RE: Pulley bolted connection torque
You have a contact area and a bolt tension. Calculate contact pressure, which gets you the force limit between the faces.
If this is a real-world application, however, you may also need to account for the fact that the belt tension puts a bending load on that SHCS. This is not ideal because it can fail the SHCS but also because it has the effect of reducing contact area between the parts (as the 'top' of the pulley deflects away from the shaft and the contact area tips up on edge).
This condition makes it harder to keep the parts fixed, as the result is a net reduction in torque capacity.
RE: Pulley bolted connection torque
RE: Pulley bolted connection torque
Go to Bolt Science and read up on bolt failures. Basically, bolts come loose when there is a mechanism that rotates them, such as the torque your pulley is trying to transmit.
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JHG
RE: Pulley bolted connection torque
But to drawoh's point, whichever direction the pulley absorbs power in during service must be known, so that a left or right hand thread fastener can be properly chose.
You need to choose the threadform so that the service torque does not loosen the fastener.
If it absorbs or transmits power in both directions, you need to pick a more robust arrangement.
RE: Pulley bolted connection torque
Is this an idler pulley, only subjected to radial load from a belt, or is the plan to transmit torque also?
If by chance the bottom of the bore or the end of the shaft are machined convex the diameter at which the friction is applied will be quite small, reducing the amount of torque resistance considerably.
RE: Pulley bolted connection torque
RE: Pulley bolted connection torque
I second this. Works good on the crank damper of many engines.
There are a lot of ways to do pulley->shaft that will be reliable. The one you have shown there isn't one of them.
It would even be better to do a bolt circle of M3's if you absolutely must have a face-to-face connection.
RE: Pulley bolted connection torque
RE: Pulley bolted connection torque
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Pulley bolted connection torque
I understand your concerns, the reason this came about is the shop has limited manufacturing capabilities and the steel shaft is case hardened to ~60 HRC. It's to be used in a non critical application and will transmit around 6Nm of torque in both directions. My calculations show the shaft will see a radial load of around 140N or 32lb.
I need a simple connection so I intended to use Loctite 648 retaining compound but having no experience with using the retaining compound I want to err on the side of caution a little, has anyone used this stuff before and do you think it'll be sufficient? I've heard it's the bees knees. http://www.loctite.co.uk/loctite-4087.htm?nodeid=8...
RE: Pulley bolted connection torque
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Pulley bolted connection torque
I think a more typical damper connection on modern passenger car engines is a close slip fit damper, with a small key to align damper timing marks and timing sprockets properly, with a single relatively large bolt tightened HARD to clamp all the components against a shoulder on the crankshaft to handle belt driven accessories, and maybe most important, so no micromotions occur.
The successful recipe is Big fastener torque for high clamping force and resulting friction, and maximum interspecies contact diameter where the friction is applied so it can resist maximum torquage during operation.
Skimp on the installation torque, and the attachement shows what WILL be the result with a keyed application.
Without, a key the pulley will just slip and tear things up a bit.
RE: Pulley bolted connection torque
Loctite 648 is green stuff, right?
We used green Loctite (622?) to make sure dowel pins were retained. At some point, we decided the anodized aluminium had to be Alodined. The pins did not come out. We had to machine them out. Loctite shaft retaining compound is very effective. Follow the manufacturer's instructions. Since we were using aluminium and stainless steel, we applied primer.
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JHG
RE: Pulley bolted connection torque
Maybe this is done all the time and I've just never seen it.
RE: Pulley bolted connection torque
What?
RE: Pulley bolted connection torque
RE: Pulley bolted connection torque
Really?
Contact pressure, coefficient of friction, and mean radius are all that's required to calculate the torque limit of the interface. This isn't hard.
RE: Pulley bolted connection torque
No, not hard at all when you have [b]all the correct terms[/b].
RE: Pulley bolted connection torque
RE: Pulley bolted connection torque
RE: Pulley bolted connection torque
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: Pulley bolted connection torque
RE: Pulley bolted connection torque
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.
RE: Pulley bolted connection torque