KK9A wrote:
"One could certainly design a better method of clamping than the Orion mast
clamp, however apparently the rotator will destruct when connected to very
large antennas. I spent some time looking at K7NV's prop pitch rotators and
some of them appear to use a mast clamp similar to the Orion. Is this the
same problematic clamp that is on the Orion 2800? Some K7NV's prop pitch
rotators use his mast clamp, which apprears to be a better option." ......
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John,
It's the same clamp parts but built differently....
Some people want or need the OR2800 kind of clamp to accomodate odd sized masts.
I usually only make my type of clamps for the most common sizes, 2", 2 7/8" and
3". Making custom "one offs" is pretty expensive.
So, I get the clamp parts from M2 and rework them so that:
1) The base plate flathead fasteners that connect to the prop pitch are
increased to a larger size so they won't shear off so easily. I've received 4
prop pitch rotators for rebuild with the original fasteners sheared off. Often
the reason for failure is the loosening of these fasteners and then the
corrosion in the threads locking them in the loose state. These flathead screws
should be installed with a thread locking compound that resists loosening and
keeps water out of the threads.
I use the base plate with the larger dia bolt circle. This connection is good
for around 36,000 in-lb of torque, using a shear strength for the fasteners of
50% of Ultimate. The smaller bolt pattern with the smaller fasteners is good
for about 16,500 in-lbs
2) The clamp jaws are resurfaced to fit the actual mast that will be in it,
along the full length of 4 or more ribs (approx 1/8" wide contact surface) on
each jaw, instead of just a few small spots like they are with the raw casting.
3) The casting bumps are removed around the clamp jaw fastener holes so they
won't loosen as the bumps wear down.
4) The cap screws holding the jaws to the base plate are changed to a higher
strength alloy, and are longer with nuts added to the bottom side of the plate,
because a 3/8" dia thread in a 3/8" thick plate is not enough. Standard thread
engagement should be at least 1.5 x the diameter (or 9/16").
Then I send the unit with a big high strength bolt to pin the mast to the
clamp. Haven't heard of problems with any of these so far.
Pinning the mast to the clamp doesn't void the warranty, because the prop pitch
gear train (at least like I build them) can't be broken.
73, Kurt, K7NV
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