Re: [ATM] diagonal flat testing

["Jerry B. Hillman" <JBHillman@ev1.net>]

Hi all,
Mirror cell is  Plop designed 18pt.
It is built from two pieces of 3/4" plywood. The back piece has 6 holes
drilled into it spaced 60 degrees around and placed two inches in from the
edge.  Three of these, spaced 120 degrees apart, have inserts to hold a 1/4"
x 20 bolt.  The other three are drilled out to allow a 1/4" bolt to pass
through.
The other piece of plywood actually holds the mirror.  It has three holes in
the back, with inserts to hold a 1/4" x 20 bolt.  These three bolts allow
collimation. A spring between the two sheets of plywood and each of these
bolts provide tension on the bolts.  The other three bolts are there to lock
the adjutments in place.
The 18 points of support are built from 1/8" thick aluminum triangles cut to
size specified in plop generated diagram and placed in position by that
diagram.  All trianges have small countersunk holes for placement of
bearings to rest on. The bottom three triangles rest on a 1/4" ball bearing
attached to a slightly counter sunk hole in the plywood.  A thin sheet of
plastic holds these pieces in alignment. The remaining nine triangles rest
on 1/4" bearings countersunk in the first three triangles.  All bearing
joints between triangles are made with small amounts of silicone to keep the
joints pliable. Thin sheets of plastic hold the top nine triangles in
alignment.  The mirror rests on teflon disks 1/2" in diameter.  Mirror is
held in position by a sling positioned to be exactly centered horizontally
on the edge of the mirror. This sling is made of ball chain to eliminate the
possibility of binding and minimize stretching.
Both points where the sling is attached to the cell have a small flange that
extends out over the mirror to prevent the mirror from tipping forward out
of the cell.  These flanges clear the mirror by 1/16"  Extremely horizontal
positioning of the OTA allows the mirror to fall forward slightly but I
considered this unimportant since I don't use the telescope for viewing in
that position anyway. Upside down trees are not interesting targets.

Clear skies, Jerry




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