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Originally Posted by spudrick
Thanks for your help Ian, Will get it fixed this weekend.  |
No worries Terry, glad to be of help.
The Sampson mount as a standard unit was okay for visual use, but horrible to align as the mount was really a knock off design based on a mixture of the old Cave, Edmund Scientific and Fullerscopes Broadhurst and Clarkeson (UK) mount designs of the late 50s and early 60s.
I extensively modified my mount from '75 to '84 to get it not only operating well but to make it far easier to setup, some of the mods I made were:
RA and DEC locks:
If you remove an existing lock you can have the thread identified at any industrial fastner specialist.
From memory they use a BSW thread. I dissassembled my unit, pulled the locks and retapped the thread to accept a standard tri-nut unit as used in stage lighting (Par 56/64 cans). These tri-nuts are available from any stage lighting supplier for a couple of bucks each.
Leg levellers:
I drilled and tapped the end of each leg to take a stainless steel capscrew to act as a leg leveller. On my legset there were threaded holes on the underside of the round tip of each leg. Why capscrews? Though needing an Allen key to use, they are lower profile and less likely to be walked in to at night and far less tempting for people to want to play with.
The Pier:
Before modifying the pier make sure the top of the pier tube is squared off accurately. I ran my pier tube through a lathe to make sure it was accurate to 1/1000th of an inch. This step really isn't needed though as there's so much slop in the RA mount cap anyway.
After squaring the pier tube I plugged the bottom of the pier, just above the leg mounting bolts with a bit of chipboard and gaffa taped the gaps then filled the pier with concrete. It not only reduced vibration but also made the mount far more stable. A lighter weight version would be to fill the pier with expanding foam as used in small boat floatation cells
The mount (RA) Cap:
A horrific bit of design work this! Slop laden, with a single fastening screw it's truly a nightmare.
If you have access to a lathe and milling machine I can supply you with a couple of suggested ways of sorting out the cap, otherwise the best you can do is shim the cap to reduce slop and add 2 extra locking screws at 120° intervals around the cap. I highly recommend replacing the existing tightening bolt (flat screwdriver head) with capscrews.
Other fun:
There's a couple of other nightmares with the Sampson mount, the biggest of which is actually getting the swine polar aligned accurately. As there's no provision in the standard mount for fine adjustments you can either build some (late, mill needed) or use the knockometer method for azimuth adjustment and a variety of methods involving car jacks, lumps of wood etc for the RA polar axis altitude adjustment.
Cheers,
Ian
