I do not have enough mechanical knowledge to understand why the clamping
surface area would not matter. Are you saying three center punch sized
points with the same clamping pressure would hold the mast just as well?
DOM tubing has pretty tight tolerances so results should be consistent. A Ø2
tube has a +.006 -.000 tolerance so it will be reasonably round. A portion
of the K7NV clamping tube is cut away so it should form to the mast when
tightening. If there is a big glob of mast galvanizing in the mating area
it should be cleaned off. Of course the K7NV clamp will not tighten well on
1 1/2" pipe. I have two K7NV rotators with Ø3" masts and they were tightened
just using combination wrenches. So far I have not experienced slippage with
reasonably large antennas. I am sorry to hear that yours does not work, I
wonder why?
John KK9A
From: Richard Karlquist [mailto:richard@karlquist.com]
Sent: Tuesday, November 8, 2022 5:29 PM
To: john@kk9a.com
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] More friction needed
I have one of the K7NV clamps, which is on my K7NV prop-pitch.
I agree that Kurt's passing was a great loss to us, but as far as this
clamp is concerned, it is possibly "too brilliant ... by half". The trouble
is that the target mast must be:
1. Perfectly smooth.
2. Have excellent "circularity", as opposed to "eccentricity".
3. Have a diameter very close to 2.000 inches.
or else it may only sort of work, but not as well as you might think.
There is a certain amount of "luck" in meeting these requirements.
Then there is "physics":
Static Friction (IE "stiction") is a function of total clamping
pressure, period. Having a lot of area doesn't help. In defense
of the K7NV clamp, it is designed to have multiple clamping bolts,
so we can count the combined clamping pressure of the N bolts.
More physics: read up on cylinder head bolt design and the need
for the head bolts to be elastic. Inelastic U-clamp bolts deform
the clamp instead of stretching.
If your K7NV clamp works really well, then I am happy for
you ... that you were lucky, or maybe you tightened it with a
24 inch breaker bar.
I will also say that it is way better than the M2 clamp (also own
one of those).
---
Rick Karlquist
N6RK
On 2022-11-08 13:46, john@kk9a.com wrote:
I don't think adding a friction material will help. There are better mast
clamp designs out there. K7NV(sk) came up with a brilliant idea of clamping
a round mast using a round clamp (imagine that). I thought that you also
manufactured a replacement clamp that used u-bolts which could be properly
tightened and remain tight.
John KK9A
k7lxc wrote:
Howdy, TowerTalkians -
I need more friction between an M2 mast clamp and the mast. How could I
do that? What materials would work? Tnx. Cheers,Steve K7LXCCell:
206-890-4188
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