----- Original Message -----
From: "Tom Witt" <wittsend@jps.net>
To: <tigers@autox.team.net>
Sent: Monday, June 13, 2005 8:40 PM
Subject: Re: Front crossmember
> 2. I have cut threads with a die in both grade 8 bolts and the Tiger rack
> arms. I did extesive back cutting (maybe ever 1/12th of a turn or less).
> Yes, it took a long time. Yes, at the end the dies didn't look great, but
> they were not that bad either. I would think one "might" actually cut at
> least another set with these (left/right thread) $9 dies. Extensively
rotary
> wire brushing the threads removes the small amount of burrs that were
left.
Sometimes the theory of doing
> things and the reality are two different things.
> Sometimes you just have try and see for yourself.
> Tom Witt
If you were to take a microscope and look at the roots of the threads you
cut, you would find lots of small tears. All of those are initiation points
for fatigue cracks.
The theory says that a cut thread has far less fatigue resistance than a
proper rolled thread.
Fatigue is as real world as it gets.
The home made threads you have will not have nearly the fatigue life that
rolled threads will.
That doesn't mean it will fail tomorrow or even 20k miles from now. But like
fulcrum pins, it will fail.
I just hope that you are going slow when the time comes for you to see for
yourself.
Somebody else mentioned Carrol Smiths book on fasteners. I highly recommend
it. It is written by and engineer who knows race cars. But it is written
for a non technical audience.
Carrol has a gift of explaining esoteric topics is a clear and straight
forward manner.
Erich
|