[TowerTalk] More on Orion mast clamps

Mark . n1lo at hotmail.com
Thu Mar 2 18:32:24 EST 2006

Howdy Steve et all;

I think your proposed solution will work with any or all of the following 
a) Use a locking compound between the inserts and the mast to mechanically 
bond them together. The extra contact surface area you are adding will allow 
a *very* strong bond.

b) Use an insert material that is scored or knurled and hard enough to bite 
into the mast like vise jaws or vice-grip locking pliers.

c) Replace the existing mast clamp bolts with larger diameter ones.

Rick, N6RK, is spot-on when he pointed out that the *frictional force* (not 
adhesive bonding) between two objects is largely *independent of contact 

<<...snip...The physics of the slip-nott don't necessarily make sense.  If
you have a certain coefficient of friction, and a certain amount
of clamping force, in theory, it shouldn't matter if you distribute
the force over a large area with a slip nott or a smaller area.
The slip-nott is not engineered to have more total clamping force.
Maybe it works for reasons I don't understand. Rick N6RK >>

The bonding force of an adhesive is very dependent on the contact area.


There are two ways to increase the friction force:

1) Increase the total force that pushes the objects together.

2) Increase the coefficient of friction between the contacting surfaces.

On the other hand, using an adhesive, such as a locking compound, to 
mechanically bond the surfaces together, is largely independent of the 
clamping forces. In this case, extra contact area *will* increase the 
strength of the bond.

Both methods can be applied together to help grip a mast.

In the case of mast clamps:

#1 above can be accomplished by:
    a) Adding more total clamps or clamp bolts to push the surfaces together 
(they all add up).
    b) Replacing smaller bolts with larger ones that can hold more tension 
(if the clamp body/saddle
       can take the extra stress).

#2 above can be accomplished by:
    a) Roughing up the contacting surfaces, or using different materials 
that have higher friction.
    b) Adding knurling or longitudinal cut grooves into the harder of the 
two surfaces to allow it
        to bite into the softer surface. Look at the jaws on your bench 
vise. These sharp edges force
         material to be sheared off before the two surfaces will slip. Two 
examples of the extreme
         extension of this process are woodruff/shaft keys and spline joints 
in prop pitch devices.
    c) Adding cemented grit (a la guy grips).

Now, the reason the Slippnot works is by 1a above: The Slippnot adds more 
grip area but more importantly, *more clamping bolts*. The two tabs on it 
lock it to the rotator's existing clamp, effectively creating a composite 
clamp having more total clamping force.

Hope this helps.


Steve wrote:

<< Howdy, TowerTalkians --
    Tnx to all for their input on the Orion and its  mast clamping problems.
While I've seen some bolt stretch that is probably a  contributing factor to
mast slippage, it seems that the main problem is that  there isn't much 
area on the clamps to really hold a big torsional load.  While the SlippNott
may help, it hasn't been verified that it'll actually fit  the Orion since 
was designed for Hy-Gain rotators.

    So it occurred to me that if we added more surface  area to the clamps,
that would probably take care of the slippage problem. My  proposed solution 
to get some relatively thin pieces of 2" ID pipe or tubing  and weld a piece
onto each clamp since there's plenty of scope left in the  clamps for this
sized mast. This should significantly add holding power to the  rotator and
inexpensively to boot...snip...Cheers, Steve  K7LXC >>

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