We are having issues with over torquing wheels on racing karts. Results in snapped studs that are threaded into aluminum hubs. Anyone got some guidance or links to the torque spec for running an 8mm 8.2 stud into a high grade aluminum casting/forging?
Some good info here:
Do you mean you are using an 8.8 grade fastener? If the studs are breaking perhaps you should substitute 10.9 or 12.9. Here is a decent table with some good info on strengths and applications
Pete RoyJ wrote:
You generally run those in once. 8.2 has been addressed. Why are you not using a thread locker to set the stud?
Put a nut on one side of stud, put stud though a drilled plate and torque other side using a proper nut and ramp up testing to destruction to see at what torque value it fails at.
We recently had some studs fail in product we make when torqued to values we have used for years.
Wes
Are you saying that the stud broke, or that the stud pulled out of the aluminum hub?
Cheers,
Bruce (bruceinbangkokatgmaildotcom)
Essentially studs are not installed the way you seem to be planning. Studs use an over size thread on the end to be installed into the parent metal and are simply driven to the designed depth.
If you are concerned about the security of the installed stud you could use one of the various locking substances which are made for various services - easy to remove, never to be removed, etc.
I wonder why you are using an impact wrench? Speed? But if the impact wrench is causing the problem why not try limiting the torque that the wrench can produce?
Cheers,
Bruce (bruceinbangkokatgmaildotcom)
If this is the stud between two halves of the two piece wheel, I'd countersink a recess in the rear section and use bolts, with red Loctite if you want to leave the threads alone. The clamping force would be more reliable. Make them more like the headed and knurled studs on car hubs that they are used to, that can't pull out. KISS.
Threaded studs like you describe have this annoying habit of coming out at the threads instead of the nut if the nut has rusted or stuck on a bit, and you are depending on the softer aluminum alloy as a critical stressed member.
And if they don't notice the stick-out of the studs getting longer than the others (or they all start backing out at the same time) you could have a failure during a race.
You can't stop them from using rattle guns,"that's Real Racing!" But if you supply the guns and lock-out the torque adjustment settings you can limit the torque applied. Might be the better route, even if you have to pay more for guns that can limit the torque to where you want it. Tell them a tall tale if you have to, "These are the Real High-Speed Guns like they use in NASCAR!"
That, or take away the 1/2" full-size impact guns and hand them 1/4" air ratchets (on a restricted air line at 30 PSI so they can't go much past snugged down) and a Clicker torque wrench.
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Given that the 8mm size he specifies is essentially 5/16", it won't take much to over-torque the studs with an air driven impact wrench.
I *think* that what he was saying was that the studs were being broken off from excess torque, and the headed and knurled ones won't do any better in the face of a 1/2" impact wrench.
The 1/4" ones might be a good choice -- about the same drive to stud diameter ratio as with normal automotive studs and 1/2" drive guns.
Enjoy, DoN.
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