On 09/06/2014 08:38, Peter Taylor wrote:
"dennis@home" wrote:

http://www.cameragrip.co.uk/acatalog...on_bushes.html

Thanks Dennis, that's a very useful resource I hadn't found before.

Here's a pic of the tripod:
http://www.euphonium.plus.com/images...ripod_head.jpg

The tripod has a flat top plate with a hole about 80mm diameter in the
centre, through which the brass fixing screw projects. The screw is free to
move around in the hole to enable the theodolite to be positioned accurately
over a point on the ground. This means I can't use the conversion bushes,
and the only way I can think of to keep the screwsolidly in a fixed position
is to use a brass bridge spanning across the hole, drilled and tapped
5/8" UNC for the screw, and this bit works fine. The problem is the bridge
needs to be min. 10mm thick, otherwise the end of the screw projects above
the surface, and that's too thick for any camera screws I've seen till now,
which is why I was intending to use a bolt.

The screw in your link with 15mm thread length might be long enough, but
it still leaves only 5mm thread above the bridge and I'm not sure that's
going to be really secure, but I'm going to order some to try.

Discussing it with a friend yesterday he suggested reducing the thickness of
the bridge locally for the screw using a spotface cutter, which means the
15mm screw will be OK. It would also let me use a circlip to retain the
screw.

Getting there slowly! Thanks very much for your link.

This lot will do custom engineering for a price (as will Telescope House).

http://srb-photographic.co.uk/

They also have a lot of other useful and rare photographic goodies.

--
Regards,
Martin Brown