[TowerTalk] Orion mast clamp question

[Grant Saviers]

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 at 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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