Making or Buying a Equatorial Mount

In message , Chris.B
writes
Jonathan Silverlight wrote in message
...

My one problem with the Fullerscopes mounts was that the mild steel
shafts rusted even when kept dry. How do you get round that?

I have the same problem. Even dew makes them rust. I plan to replace
them with stainless steel when the right size turns up at work. It is
only available in 5 metres lengths and in production order sizes. The
effort of increasing the shaft size on the mountings themselves. With
all the problems of accurately opening up the holes in the castings,
wormwheels, setting circles, weights, clamps, oilite bearings etc is
probably just not worth it. So I'm still hoping for some metric
stainless stock very close to the original Imperial sizes. Turning
down (the very tough) standard 35mm stainless steel (acid resisting)
bar accurately to the original 1.25" (31.75mm) in the length required
for the MkIV declination shaft would be quite an engineering
challenge.

My Mark III is long retired - I should get it working again :-) - but I
spent a long time looking for stainless steel of the right size. I ended
up using aluminium, which was far from ideal but didn't corrode and
could be reduced to the right size.
I wonder why Fullerscopes didn't use stainless steel. Or plated steel,
like my Vixen mount.
--
"Forty millions of miles it was from us, more than forty millions of miles of
void"

Jonathan Silverlight wrote in message ...

My Mark III is long retired - I should get it working again :-) - but I
spent a long time looking for stainless steel of the right size. I ended
up using aluminium, which was far from ideal but didn't corrode and
could be reduced to the right size.
I wonder why Fullerscopes didn't use stainless steel. Or plated steel,
like my Vixen mount.

I'm not sure aluminium is as inherently stiff as steel. But it must
have lightened the mount quite a bit as the weight is mostly in the
steel shafts. Since high rotational speeds are not involved the
bearing qualities are probably irrelevant while still well lubricated.

The use of stainless steel would have added significantly to the cost
of the mountings. Fullerscopes chrome plated their shafts later.
Presumably once the rust problem showed up. My Mk111 has chrome plated
shafts and still rusted readily where the counter-weights & clamping
screws cut through the chrome.

I have just removed the shafts from my Mk111 to see how they are held
in place. The polar axis is held by a headless, taper-pointed screw.
While the declination shaft is held by a simple hammered in pin. I
tried to use a stud extractor on both and failed to move them. So
drilled out the pin and screw in 1mm larger steps until they came
loose. I'll put the sordid images & details on the website to save
boring the casual reader.

The shafts are 25.35 over most of their length. But 25.45 where they
are lightly knurled for better grip in the short length that fits in
the castings.

Now I really do have to find some stainless steel bar (& quickly
too). I don't fancy putting the rusty chromed shafts back in again.
I'll probably use industrial Loctite to fix the stainless steel shafts
rather than using pins and screws.

Chris.B

http://mysite.freeserve.com/fullerscopes_mk3