ATM 8" refractor project

[David Margrave <davidma@eskimo.com>]

Hello,

I'm going to be particpating in the 8" refractor class at the western
washington university telescope optics workshop.  I want to prepare a few
things in advance: spherometer and wedge tester.

For the spherometer, there seems to be a lot of talk back and forth about
what is suitable for a dial indicator/micrometer.  Some people have said
that the cheap .001" dial indicator is fine.  Others say that you need
.0001", which would require either a micrometer spindle, dial test
indicator, or precision dial indicator.  I have found .0001" dial
indicators with very limited travel, .0005" with suitable travel, and of
course the standard cheap .001", but nothing of the sort that Roger
Ceragioli calls for in his instructions: .0001" with 1/4" travel.  Is it
simpler to just take a hacksaw to a micrometer to salvage the spindle?

What size base should I be making for working on an 8" lens?  I'd guess
5-6".  I have access to a machine shop which I'll make use of for this
project.   Should I try to make a fancy base with multiple tapped holes
for the feet, or just keep it simple and permanently fasten the feet.
I've seen some plans for adjustable spherometers of this sort which seem
interesting.

For the wedge tester, I think I've got the general idea.  I'm going to
take a sheet of melamine (laminated particle board), and put in some
threaded inserts for holding the feet and the stops, and for the dial
indicator post.    No need for metal or high precision in the construction
of a wedge tester, right?

I have an idea for a relatively simple do-it-yourself optical tube: with a
router cut some rings out of aluminum plate, take a sheet of aluminum and
run it through a slip roll, put a 'step' on one edge to make for a
prettier seam, and then screw or rivet the skin to the frame of rings.  I
don't have the background to make the design decisions however (how many
rings, how thick a skin, etc).  For the lens I'll be working oon, I think
I'm looking at a 10' tube, so I may build it in two or three sections
which can be bolted together.  I'm also seeking information on lens cell
design.

Thanks,

Dave