This appears to have said it all.
It sure seems, with most rotators anyway, we are between a rock and a
hard place (maybe not hard enough, hi). Aluminum threads are being
pulled on by a steel bolt that seems to require distortion to stay in
place. Hardened lockwashers that (in order to work) pierce the plating
and allow corrosion.
I guess it's blue loctite, a firm twist and (mercy) at least yearly
inspections.
I think I'm convinced.
Mike N2MG
> -----Original Message-----
> From: w8ji.tom [SMTP:w8ji.tom@MCIONE.com]
> Sent: Friday, January 29, 1999 10:09 AM
> To: gbay; TowerTalk
> Subject: Re: [TowerTalk] greased bolts?
>
>
> Hi Gary,
>
> My experience with this comes from building race cars and high
> performance
> engines.
>
> When a $1.00 bolt failure costs 1/5th of a years income, a person
> learns
> what not to do.
>
> > reassemble everything. I've followed the thread about using
> lock-tite.
> > However, the manual says to use grease and so does the local machine
> shop.
> > Anything wrong with using plain old grease on the threads?
>
> I use "grease" on wheel lug nuts, and oil on connecting rod threads,
> but in
> those
> applications the bolt and nut is actually distorted by the tension
> applied
> when the bolt is torqued. It is the distortion of the hardware that
> "locks"
> the bolts firmly in place without threadlocking materials or devices.
>
> If you aren't tightening the bolt enough to stretch the bolt and
> distort
> the threads, grease or oil is generally a poor idea. Grease is
> generally a
> bad idea
> anyway, because the viscosity is too high and the threads "float" on
> the
> grease when torqued lightly. It's OK if the application is low stress,
> but
> not if the bolt is worked anywhere more than a few percent of it's
> rating.
>
> I'm virtually 100% positive grease is a bad idea in this case. Even if
> the
> rotor and bolt are high enough quality to allow you to stretch the
> bolt
> enough to "lock it" in place without a failure, the rotor plate is
> probably
> not hard enough. If the "soft" plate compresses even a few thousandths
> of
> an inch, you'll loose all the bolt locking when the bolt shaft is
> short in
> length and not stretched more than the wear amount of the plate.
>
> I'd use good bolts and a soft-grade threadlocking compound and torque
> a
> safe amount for the rotor threads. The compound will protect and
> lubricate
> the threads when you install the bolts, and prevent them from falling
> out
> even if the rotor plate compresses or wears at the holes. Since the
> bolts
> are mostly in shear, and not in stretch or compression, the main
> problem
> should be "falling out" and not hardware failure.
>
> A large OD, thick, and *hardened* washer that PROPERLY fits the bolt
> shaft
> would be a big help, because it would spread the load on the rotor
> plate.
> The weak point then would surely be the rotor case threads.
>
> Remember, either you lock the bolt with something or you stretch it
> more
> than the amount everything else changes. If you don't, it will
> eventually
> get loose. Grease or oil is only a good idea when the bolt is
> stretched by
> installation torque more than the amount of give in the other
> materials.
>
> 73 Tom
>
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