Thread problems... [RE-wrenches]

[Jim Duncan]

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Two messages that I read the last few days applied to threaded fasteners 
with defects. Galv buildup and microscopic fractures. Both reminded me 
of my good 'ol days as a toolmaker and the horrors faced with bum 
threads in expensive little pieces of metal.
Most roof-mount risers, stanchions or whatever you call them, are 
mass-produced from 6061-T6 aluminum and any threaded holes are power 
tapped. 
After hundreds or even thousands, of threaded holes produced with one 
tap, the finished ID threads will develop those microscopic fractures.
That's not so bad when the final assembly includes properly cleaning 
threads beforehand. But any outdoor dusty/windy situiation, reaching in 
a box of bolts and driving it home leaves a lot of room for 
contamination. 
In particular, tightning a stainless steel bolt into aluminum threads 
and the bolt gets tight too soon. That's probably a sign that the 
threads are beginning to gall. You will never get the bolt to come out 
if you force it in until it's tight. Stainless and aluminum are a 
notoriously incompatiable pair.
Some grades of aluminum we referred to as recycled beer cans because it 
was so "sticky" when machined. And with the boatloads of imported metals 
coming to our shores, you have no idea what the purity of the metal is.
Anyway, spend a few bucks on a can of anti-sieze compound and it will be 
the best money spent since your cordless drill. The good stuff has 
finely powdered nickel in a petro based grease. It only takes a tiny 
amount applied with the brush-in-can to insure that the threads won't 
gall. Even with some contamination it makes a big difference. 
It will also make any torque readings much more accurate. 
BTW It's the only type of lubrication you should ever put on threads 
unless the manufacturer says different.
Jim Duncan
North Texas Renewable Energy Inc
Fort Worth, Texas

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