Re: ATM Looking for mirror cell ideas

["Bill Prewitt" <bprewitt@newreach.net>]

I don't have any pictures yet, but I just completed one & will have it on
the page in a week or so. The star test shows no
astigmatism or "pinched cell" effect.

Basically, you use a router to cut one 3/4" plywood disk to the mirror
diameter and another to the inside tube diameter.
Drill 3/8" holes in the centers as a bearing surface for a 1" marble or
steel ball. 

Near the outside edge of the smaller disk, drill holes for three carriage
bolts, to extend through both disks, the gap, and an inch
beyond. Countersink on mirror-side of small disk to hide the bolt heads.
Capture the ball with a "picket fence" of
brads to the rear of the small disk.

Assemble as: carriage bolt, small disk, fender washer, compression spring,
fender washer, large disk, fender washer, and 
wingnut times three. Epoxy the carriage bolt heads to the small disk,
leaving a flush mirror-side surface. 
Attach mirror by placing three nickels at edge near bolt heads, and
squeezing three 1" mounds of RTV about 1 1/2 to 2" in 
from edge at midpoints between nickels. (I've seen a cell-design program
"somewhere" that calculates exact positions.)

Remove nickels after 24 hours and enjoy. You may wish to add three padded
metal clips to secure the mirror in case of 
separation- don't touch the glass, just be close.

Unless you have a very thin 8" mirror, this cell should work just fine.
Also, University Optics sells sand-cast aluminum cells for 
less than $50, if you don't trust glue.

         Good luck,
         Bill Prewitt



Paltry first attempt at a home page:
http://www.newreach.net/people/bprewitt/www/index.html


>Date: Wed, 21 May 1997 20:57:29 -0400
>From: mcola@netexp.net (Mark Colasante)
>Subject: ATM Looking for mirror cell ideas
>
>I am building an 8" Dob and want to build my own mirror cell.  Does anyone
>know of any resources that describe the construction of these? I am
>particularly interested in making one from wood and using gel/silicon
>"pockets"
>
>Thanks,
>
>Mark Colasante