Modifying fasteners

[tkelly27]

I was hoping I could get some help with securing our brake rotors. We're using hubs from a VW with M12X1.5 studs. The studs stick out the back, and that's where we're mounting the brake rotors. Following the rules, the nuts that retain the rotors to the hub should be a grade 5/metric 8.8, correct? Our problem is that standard size thickness nuts won't clear the front upright support ribs, and finding the proper grade thin, or jam nuts is proving very difficult! The two alternatives are to mill down the regular sized nuts, or to mill down the ribs.

If you cut down a grade 8.8 nut, is it no longer a grade 8.8 nut? Any suggestions on where to find 8.8 jam nuts?

[Chris Lane]

The only fastener modification I would feel comfortable with is cutting bolts to length.

Start milling down nuts and you'll be asking for trouble. You are reducing the amount of thread the bolt can 'grab'.

I wouldn't be using jam nuts on this either. I would use some k-nuts. Nylocks would be susceptible to the brake heat.

I'm not sure where you're getting this grade 5/metric 8.8 rule from; the only ones that I can see that are of significance are that you must use positive locking mechanisms and have two full threads protruding from the top of the nut.

Alter the upright if you really have to. Be careful though, as you'll only want to remove as much as is absolutely necessary. If you really want to use these hubs that is.

[James Morris]

8.8 refers the UTS and the yeild of the bolt
This means that the UTS = 800N
The yield = 0.8 of UTS
The yield = 640 N

A 12.9 refers to a UTS of 1200N and a yeild of 0.9 x 1200 = 1080N

Follow?

Bolts should be roughtly tightend to 60% of yeild. This is the axial torque supplied.

You can get any bolt in any size with diffrent grades, you just have to multiply the axial torque by the cross sectional area of the bolts shank to work out the clamping torque.

Only the first 3 to 4 threads of the nut actuall 'grab' onto the bolt thread as these slightley deform under the torque and react the force.

[Mustang Mac]

As stated by Chris Lane

Start milling down nuts and you'll be asking for trouble. You are reducing the amount of thread the bolt can 'grab'.

I wouldn't be using jam nuts on this either. I would use some k-nuts. Nylocks would be susceptible to the brake heat.


As a Tech Inspector this is one area we look closely at. Remember that a failure here may cause limited or loss of braking. Cutting down a nut to clear is never a good answer. My suggestion would be to go with the k-nuts and modify the upright, making sure not to jeopardize it's integrity in the process.

[HenningO]

Originally posted by James Morris:
8.8 refers the UTS and the yeild of the bolt
This means that the UTS = 800N
The yield = 0.8 of UTS
The yield = 640 N

A 12.9 refers to a UTS of 1200N and a yeild of 0.9 x 1200 = 1080N


With N I believe James refers to N/mm^2 which is equal to MPa. Just to avoid any confusion!

Go SI-units! http://fsae.com/groupee_common/emoticons/icon_wink.gif

[James Morris]

Yep sorry my mistake, defo is MPa. In my defence it was coming up lunchtime and i was thinking of what to have in my sandwich http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif

[Chris Lane]

Oh well, that's ok then!

What was for lunch today?