[TowerTalk] Mast slipping

Mon Jul 23 09:13:08 PDT 2012

Wonder if any of y'all with this problem have ever tried coating the mating
mast and clamp interface with Red Loctite?
Real cheap to try it.  Does a terrific job of preventing movement in bolts
& nuts, you have to blast to get them loose.

Don  N7EF

On Mon, Jul 23, 2012 at 8:40 AM, K8RI <K8RI-on-TowerTalk at tm.net> wrote:

> On 7/23/2012 3:50 AM, Grant Saviers wrote:
> > No doubt one can design and spend $$$ for boom clamps that will exceed
> > the torsional strength of the mast,
>
> No one has talked about exceeding the torsional strength of the mast.
> It's been exceeding the internal strength of the rotator.
>
>   but why bother when off the shelf
> > economical hardware will do the job?   The major problem we all seem to
> > agree about is adequate clamping to the mast when it is hardened (alloy)
> > steel.  In spite of galvanizing, it is still hard and slippery - just
> > try to clamp hardened steel in a machinist hard jaw vise (which I
> > regularly do).
>
> Same here.
>
> >  So it takes a lot of contact area and a conforming
> > material to generate the friction necessary to generate sufficient
> > clamping force and hard steel on hard steel is a very poor choice.  The
> > cast aluminum surface in a DXE saddle clamp does that job well and two
> > or three of them provide plenty of contact surface compared to anything
> > I've seen in an out of the box antenna boom to mast clamp.  A u-bolt
> > holding a tube against a flat plate or against a muffler clamp style
> > saddle are recipes for trouble.
>
> Agreed.
>
>    In the first case there might be only
> > two points of contact, one on the plate and one at the apex of the
> > u-bolt unless it is perfectly sized to the tube.  In the second case,
> > the stamped saddle sides will spread out as force is applied.
> >
> > There is no benefit to having the saddle extend further than the DXE
> > single saddle clamps as there is no force from the U-bolt to provide
> > clamping force.
>
> Here we disagree, but the clamping action does reduce with distance from
> the bolt. OTOH a two inch wide saddle would give notably more grip than
> a one inch wide. saddle.
>
>    If more clamp is needed, there are the DXE "super-duty"
> > saddle clamps with two saddles and through straight bolts.
>
> I prefer two saddles on one u-bolt.
> However when it comes to anything larger than a 2" mast I prefer a
> larger clamp with straight bolts.
>
> >
> > For mast to rotator, if a split sleeve is used such as in the K7NV
> > rotator clamp there is force around much of the circumference clamping
> > the mast and maximum contact between the surfaces if tolerances are
> > correct.  see http://www.k7nv.com/proppitch/id35.htm
>
> Something similar to that is what I've been referring to. What I don't
> like about that is the asymmetrical forces exerted at the base of it.
> Of course if there is only a few thousandths clearance between loose and
> tight it wouldn't be a problem.  I'd rather see it as a split fitting as
> the 4 bolts holding it to the rotator would be the weak point and for
> that size (2 or 3") The clamp is far stronger than the attachment bolts
> and both far exceed the needed strength.
>
>   Since most masts
> > have multiple antennas, the strength needed at the rotator is a sum of
> > all the torques and the upgraded rotator clamps (over stock) are
> > probably worthwhile in many large antenna installations.
> >
> > The engineering tests show that double nuts, properly tightened are
> > superior to lock washers and the nylock nut is somewhat better as the
> > second nut.  see http://www.boltscience.com/pages/twonuts.htm  Even if
> > the nylon degrades (there are non nylon inserts as well) the double nut
> > friction still is better than a lockwasher. The most important factor is
> > sufficient bolt torque to insure the nuts stay tight.  I considered
> > mentioning using a torque wrench to get the bolts adequately tight and
> > that is definitely a good idea.   There are other choices as well to
> > insure the fastener stays tight.  Perhaps the easiest and most reliable
> > is Loctite.
>
> Agreed
>
>   The medium strength grade (blue 242) can be disassembled
> > with hand tools (no heat required).  However, the bolt surface should be
> > clean so use the Loctite to prevent SS galling.
>
> I just use what are called double sided lock nuts.  They appear to be a
> normal nut, possibly a little thicker than normal. Looking closely you
> can see two very small indentations 180 degrees apart on the flats.
> They work very well and I've never had one come loose, but you do have
> to remember to use either locktite, or neverseize to prevent galling.
> The neverseize will not normally reduce the gripping force enough to
> cause a problem.
>
>    Belleville washers are
> > used when stress or temperature cycling can cause the tension in the
> > bolt to reduce, potentially lowering the friction force holding it or
> > the nut tight,
>
> The last time I use Belleville washers was when working in industry, but
> they are certainly superior to lock washers.  That was over 35 years ago
> and I'd even forgotten about them.  I've never had conventional lock
> washers last more than a few years. SS lock washers do last, but do not
> appear to add much force. The only lock washers I've seen that worked
> well, were *big*! Big as in one inch and up.
>
>   a problem in steam lines but not likely on a tower.
> > Bellevilles are very high rate springs that are not flattened at the
>
> The use of Belleville might be indicated with large Aluminum boom to
> mast clamps with SS bolts of 3/8" and up where the expansion ratio
> between the Al and SS is substantial.  Probably not needed on tribander
> and WARC 7 size antennas, but they certainly should not hurt.
>
> > required bolt torque/tension. There is also a ratcheting 2 washer
> > combination (Nord-Locks) that causes the tension to increase if the
> > assembly starts to unthread but these are about $3 each in 3/8 SS from
> > Fastenal (if you can find them ).  Regular split ring lockwashers are
> > now recognized as just about useless, they flatten at required torques
>
> In over 50 years I've only had one boom to mast clamp come loose and
> that was on a Hy-Gain TH-5, maybe 8 or 10 years ago.
>
> One of my pet peeves is hardware on Force 12 antennas. So far I like the
> antennas and would get them again, but I've had to replace all the
> U-bolts with SS saddle clamps.  I had to soak the nuts with PB-Blaster
> for about 24 hours to get them off and then I still twisted off 3 of
> them.  That is a lot of saddle clamps and IIRC it cost over $100 to
> replace them with the saddle clamps on the C19 XR. Now I'd like to
> replace that with the C31 XR.
>
> BTW although those saddle clamps are a bit pricey, you can't build them
> yourself for that price unless you just happen to have some 1" thick Al
> plate or rectangular rod handy or one whale of a good source.
>
> 73
>
> Roger (K8RI)
> <snip>
>
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