ATM 4" scope plans...

[Ron Forrester <rjf@zero-ping.com>]

Some of you may have read about my 'friends and family' scope making
plan, where I plan to make a handful of simple 4" scopes as gifts for
friends and family (to encourage them to look up once in a while).

I have the glass for the first 3 of these, and I wanted to run my
basic plans by you all to get a reality check. As a point of
information, my only experience to date is the 6" f/6 (spherical)
dob scope I just completed

- first goal -- keep it simple and inexpensive.

- 4" f/5's. Is this a reasonable focal length? Will it be difficult to
parabolize (unlike the 6", I want to go all the way with these as
experience for the 16" will do for myself next).

- PVC pipe for the OTA -- I know it sweats, and isn't too stable, but
I don't see many non-wood alternatives for this, and this is small
enough I don't think it will hurt (we're talking like 18" total ota
length here).

- A simple fork type mount -- I am envisioning these as being table
top scopes, not used for anything but casual moon and planet gazing,
and I really want to make them easy to setup, move, and not be in
multiple pieces. Is a fork mount (wood?) reasonable?

- A stiff single wire diagonal holder.

- Some kind of homemade friction fit focuser -- I have heard of these
being made from pipe fittings, etc, is that right?

- A simple push/pull bolt cell made from some thin hardwood.

- Should I make the diagonals too? Will I save much money? 

So that is the plan in a nutshell. I am trying to keep construction of
each under $100. The glass was $20, so I have $80 left for the rest.

Any comments, suggestions, etc would be really appreciated.

Thanks.
rjf&