moe.taco
10-21-2005, 06:13 PM
As part of my job training I was required to take a class on fasteners (aka nuts and bolts) put on by Bowman distr. The information I came away with was extremely fascinating and I thought I should share this info with you guys. I was blown away by how something so simple could be so complicated. I am also working on a torque spec spreadsheet for grade 5 & 8 bolts and nuts
Here are a few things(do's and don'ts):
-Never, ever use lock washers or Nylock nuts!!! The friction required to compress the washer, or thread the nylon will throw off the torque value by as much as 50%. Use 'all steel' lock nuts or loctite blue if you are worried something might come loose
-Be careful how you handle bolts. The oil on your fingers can lower the torque value substatially. The same thing holds true if you use anti-sieze on the bolt. Applying "dry" torque values to lubed bolts will cause failure.
- A nut is a one time use item. After its initial use the threads have stretched(less friction) to accomodate the bolt. Re-using a nut can reduce the clamping force by as much as 50% per use.
-If using gr.5 or gr. 8 bolts use only hardened washers. If the washers are not hardened it will throw off the torque value substantially.
-A washer is side specific. There is a smooth side and a sharp side. the smooth side should face the head of the bolt. If you put the sharp side against the head you can cut/crack the head of the bolt.
- Use only gr.5 or 8 hardware that is marked with the appropriate dash's and a manufacturer's symbol. This is a sign of quality. If the head of the bolt has nothing on it, the strength is unknown and is considered gr.1-2.
-A quality bolt used in the right appication will fail for 2 reasons. It was over torqued(overstressed) or under torqued(not stressed enough)
Ok thats enough typin for now. There is more, but I think I hit the high points. If you guys have any questions, ask. I should have that spreadsheet up this weekend.
Pete
Here are a few things(do's and don'ts):
-Never, ever use lock washers or Nylock nuts!!! The friction required to compress the washer, or thread the nylon will throw off the torque value by as much as 50%. Use 'all steel' lock nuts or loctite blue if you are worried something might come loose
-Be careful how you handle bolts. The oil on your fingers can lower the torque value substatially. The same thing holds true if you use anti-sieze on the bolt. Applying "dry" torque values to lubed bolts will cause failure.
- A nut is a one time use item. After its initial use the threads have stretched(less friction) to accomodate the bolt. Re-using a nut can reduce the clamping force by as much as 50% per use.
-If using gr.5 or gr. 8 bolts use only hardened washers. If the washers are not hardened it will throw off the torque value substantially.
-A washer is side specific. There is a smooth side and a sharp side. the smooth side should face the head of the bolt. If you put the sharp side against the head you can cut/crack the head of the bolt.
- Use only gr.5 or 8 hardware that is marked with the appropriate dash's and a manufacturer's symbol. This is a sign of quality. If the head of the bolt has nothing on it, the strength is unknown and is considered gr.1-2.
-A quality bolt used in the right appication will fail for 2 reasons. It was over torqued(overstressed) or under torqued(not stressed enough)
Ok thats enough typin for now. There is more, but I think I hit the high points. If you guys have any questions, ask. I should have that spreadsheet up this weekend.
Pete