I have an Orion that has never slipped (80m 86ft dipole + DB36) but it
seems a common problem. Certainly has a heavy enough casting, I have
one Orion goofed casting as a door stop. The 4 cast clamping webs are
3/8" thick and 3/4 to 7/8" wide radially. The stock depth of the shallow
V clamping is 3/4" deep. Laying a 2" and 3" diameter circle template on
the cast V leaves most of the web intact. So the stock design works
with any diameter mast 2"- to nearly 4".
So if a smooth contact at mast radius works better than the cast teeth
steps, machining to size will leave plenty of material. I'd estimate
120 deg of contact per half for 3" and 90 deg for 2".
I would do the boring on a lathe. Bolt the halves to a faceplate and
clamp some aluminum spacers thickness TBD between them with the stock
bolts. Then bore with 1-1/2" diameter (what fun to put those to work!)
carbide insert boring bar. The needed boring depth is 5-5/8". Since
the opposing halves can be bored to smooth metal, accurately measuring
the cut diameter is easy. Quick to machine once the fixturing is
designed and built.
I think doing this on a mill with a 6" long 3/4" bar in a boring head
would be very ugly as you mention.
A file test showed modest surface hardness so the carbide insert should
not have difficulty.
Send me a request off list if you want a photo of the casting Orion
forget to drill the holes in for the mounting bolts to the rotator plate.
Grant KZ1W
On 7/29/2020 18:13, john@kk9a.com wrote:
It's difficult to find a good photo of an Orion mast clamp but from what I
found it does appear to be pretty rigid, it may be a little short. Your
reasoning for poor clamping over time seems logical. You certainly can set
the two halves up in a milling machine and take a bore cut to match the mast
diameter. The problem is, it is an interrupted cut which is slow so unless
you can do the work yourself it would likely be less expensive to just
purchase an aftermarket clamp. Also the machined area would have no
corrosion protection and the clamps should be stripped and re-plated.
John KK9A
k7lxc wrote:
Howdy, TowerTalkians -
IMO the Orion mast clamp is a very poor design and has 2 fatal flaws.
The first being that the finish is dimpled and the dimples get flattened
down over time and the clamp loses its grip. The second flaw is that the
teeth only provide a small fraction of a square inch of actual clamping area
- 0.1 sq.in.? - and the teeth get ground down by mast movement hence it
loosens up no matter how much you tighten it. I've sold much superior after
market clamps in the past but can't get my supplier to make more. My
question is can you hone the existing clamp for a better fit? IOW can it be
bored for a 2" or 3" mast? It'd be something like boring a cylinder to a
specified size. If the teeth were filed down, there would be much MORE
clamping area and thus the clamp would actually hold the mast. In my
experience I've only talked to a couple of owners who claimed theirs didn't
slip and ones that I've installed seemingly always slipped eventually.
Cheers,Steve K7LXC
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