On 11/7/2011 2:50 PM, K7LXC@aol.com wrote:
> Howdy --
>
> I've got a sloppy fit between a mast clamp and a mast - both steel. It
> won't shim properly so I think my only option is to pin the mast. I've
> done it a bunch of times and mostly they hold butr sometimes they don't so
> I'm
> proposing to use 2 in one direction and another two 90 degrees from the
> first two with good-sized high strength bolts. Other than the challenge of
> doing it at altitude, is there anything else I should be considering? Or is
> there another way to do it?
>
There is also the option of having an adapter made of the proper size,
for the mast, or rotator mast clamp which would probably require the
services of a machine shop.
It depends on your over all installation including the capability of the
rotator.
I'd not pin a mast holding much in the way of wind load to rotators
using spur gears and wedge brakes.
It's had on the rotator and the mast. The mass of the antennas, torsion
capabilities of the mast, the length of the mast,
and any slop in the rotator will let the antennas swing, some times a
substantial amount.
Grade 5 or 8 bolts should be plenty strong. Most hardware store and
even big box stores carry them if you ask.
However those bolts need to be *tight*. That not tightened down tight,
they need to fit tight and be close to an interference fit.
IOW you may need to *drive* them in so long as it does not bugger up the
threads. You should actually see smooth marks on the bolt from being
driven in.
Depending on the strength of the mast the bolts need to be at least
several inches apart.
IF the drilling is going to take place on the tower "up there" you need
a "v-block" fixture to make sure the hole is really perpendicular to the
mast and
comes out 180 degrees from where it went in. The "V-block" also makes
life a lot easier when it comes to actually doing the drilling. The
hole in the V-block needs to be smooth with a very hard surface of the
proper size. A "V-block" can be constructed out of a piece of steel
angle and 1/2" plate although 1" would be better. Just assembling the
two in a large vise should assure the surface of the block is
perpendicular to the pipe in both axises. A little welding is handy
here. Drill the hold from the "V" side with a small pilot drill to make
sure it's centered. Then step drill out to the proper size. Use a very
sharp drill for the last pass, or better yet, use a reamer. Here the
drill should be just a slip fit. This is drill press (or milling
machine) work, not for hand held drills. I would oil quench the block
for hardening and possibly lap the final hole for smoothness. If you
want it right it's going to take time. If you are in a hurry and the
bolts are an easy fit they *WILL* work loose and enlarge the holes.
If you have to put the holes in "up there", clamp this fixture to the
mast, drill the first hole and use it to pin the mast (it helps to do
this with an undersize drill and fixture). Then use the regular fixture
to drill the hole and ream for an interference fit. drive in all the
bolts and *then* redrill that original under size pilot hole for the
regular size bolt.
Having said all this, unless you have a rotator strong enough to hold
everything pinning the mast can result in tearing the rotator apart and
I do not recommend this approach unless using some really strong
rotators such as the prop pitch or the newer double worm gear drive
types. Yes, I know there are exceptions and somebody knows somebody who
has used a ham IV pinned to a monster for the last two decades with out
problems, but the odds are against you.
> This is a prop pitch with big antennas on it.
Which should handle the pinning nicely...depending on how BIG those
antennas really are<:-))
73
Roger (K8RI)
>
> Cheers,
> Steve K7LXC
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|