There are "stainless" hose clamps and then there are ALL stainless hose
clamps. Value engineering can result in hose clamps for which the band is
stainless but the screw isn't. How do you tell without waiting to see if
the screw becomes a rust ball that loses its grip when later tightened or
loosened? Some alloys of stainless are at least weakly magnetic so pay
attention when checking stainless with a magnet. A weak attraction is
normal for some alloys of stainless. With clamps that have stainless bands
but not stainless screws the magnet test will show strong attraction to the
screw and no or weaker attraction for the band.
As previously posted heat cycling can help get it tight and right. When
cycling the clamp (cold-hot, cold-hot, etc) you should tighten at the end
of the hot cycle before cooling the clamp to take advantage of the expansion
and contraction which is the reason for temp cycling.
If you have to make do with inferior clamps that tend to strip when
tightening, consider using two clamps, side by side and get the clamping
force you want without stripping the clamps.
73,
Patrick AF5CK.
-----Original Message-----
From: Grant Saviers
Sent: Sunday, January 27, 2013 7:17 AM
To: Jerry Gardner
Cc: Tower Talk List
Subject: Re: [TowerTalk] Hose Clamps
This could be the result of "value engineering" of the hose clamps by
MFJ, so you might consider buying new clamps from McMaster or others
that are US made "all stainless".
I also found in assembling 3x TH7's and other antennas with hose clamped
slitted tube sections that 2 or 3 tightening cycles are needed. After
some thermal cycles and a few days the stresses redistribute in the
connection. If you can create larger thermal cycles on purpose, it
helps - e.g. leave the antenna in the sun and then sprinkle with cold
water. Then retighten each clamp. So far, this has worked with no
loose elements after years of service. The boom clamps can also benefit
from this approach. Retightening bolts after a few thermal cycles is a
standard manufacturing process when fastening systems are near their
stress limits.
The small diameter clamps are the most fragile, so have some spares.
Grant KZ1W
On 1/26/2013 10:05 PM, Jerry Gardner wrote:
I'm putting together a TH-7DX and am having trouble with the hose clamps
used to hold the telescoping sections of the elements together, especially
the smaller diameter tubes.
The instructions say to tighten the clamps until the two tubes will not
slide in and out or rotate in each other. I find that if I tighten the
clamps enough so that this is so, the clamps often break (the screw
housing
bends and will no longer hold the screw).
Is there a way to tighten the clamps enough to secure the tubing without
breaking them?
73, Jerry
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