Frank, I have to disagree. The reasons you mention for not using an SAE
grade 8 fastener for the most part don't make any sense. They do not
require any special training to "install correctly" beyond the ability
to use a torque wrench, with the thought in mind that any fastener in
any application has an appropriate torque. The special methods you
speak of apply to certain applications only, such as certain automotive
cylinder heads where a torque is applied and then the fastener is
further tightened by measuring degrees of rotation. As such, these
fasteners are only good for a one time use and must be replaced if
loosened. Same when measuring stretch with a micrometer. Neither is
the case here, as you aren't going to tighten anything to a point that
is just short of the material's yield strength. Grade 8 bolts are most
definitely NOT brittle. This implies that they will shatter. And as a
mechanic with 40 years experience, I've just never seen that happen. I
have seen some shear when over torqued, and I've seen some break when
over torqued...but never shatter. If they do exhibit this type of
behavior, then the heat treating was done incorrectly in the first
place. At the typical level of torque used on say R25, you'll collapse
a tower leg before you damage a grade 8 bolt.
That said, they are totally unnecessary for the task and add needless
expense. Cheap they are not. A good quality (not hardware store) grade
5 galvanized bolt is fine for a tower. The case hardening provides a
good load bearing surface, and the underlying alloy provides appropriate
toughness. They still should be installed with a torque wrench in any
case.
73,
Doug, W5GA
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of
donovanf@starpower.net
Sent: Friday, October 19, 2007 9:26 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Galvanized grade 8 bolts
Jeff,
Please check the head markings on your galvanized Grade 8 bolts.
If they're actually Grade 8, they'll have 8 radial lines marked on
the head. The reason I ask is that I've never seen a galvanized high
strength alloy steel bolt. Grade 8 bolts are typically plated and
have a gold color.
The ASTM A490 specification for high strength bolts does not allow
galvanizing because of the high risk of reducing the strength of the
heat treated steel alloy during the hot dip galvanizing process. SAE
Grade 8 bolts use the same high strength alloy as Grade 8 but they're
less expensive (and more common in consumer stores) because the SAE
specification doesn't require testing.
I understand that some overseas manufacturers do offer mechanically
galvanized (N O T hot-dip galvanized) high strength steel alloy bolts.
I suspect they're much more expensive than plated SAE Grade 8 bolts and
they're probably not readily available in the USA.
The alloy steels used in high strength bolts are brittle and achieve
their fastening strength only when properly tensioned by
professionally trained installers with special tools and methods. Its
very unlikely that high strength bolts actually achieve any benefit in
amateur installations, and can actually be very hazardous if not
professionally installed.
My advice: Don't use high strength bolts unless you're a trained and
experienced professional. In critical applications, use ASTM A325
bolts which can be safely installed by non-professionals. In less
critical applications use SAE Grade 5. If you must use high strength
bolts, obtain the training and equipment to use them safely.
73
Frank
W3LPL
---- Original message ----
>Date: Thu, 18 Oct 2007 13:13:18 -0700 (PDT)
>From: Jeff Walker <k4bp@yahoo.com>
>Subject: [TowerTalk] Galvanized grade 8 bolts
>To: towertalk@contesting.com
>
>
>Galvanized grade 8 bolts are available in bulk at a
>VERY reasonable price from...
>
>Gulf Coast Fasteners, Inc.
>1626 Town Hurst
>Houston, Texas 77043
>
>(713) 464-1555
>
>__________________________________________________
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