I used the program
plop to
calculate the number of mirror supports needed and their positions.
An 18-point support was found to be adequate. The first plan was to
use a single plywood disc to hold all 18 points. I got as far as
siliconing the mirror to the disc when reservations set in. I post
to the ATM mail list confirmed my fear that this was unlikely to
work.
The recommendation from the list was that an
18pt floatation cell was the only way. So out came the jigsaw and
welder. The triangles are 6mm aluminium, the rest is steel. I found
that printing the graphic output from plop onto acetate at full size
helped when putting it all together.
The supports points were made with small
copper discs with a small portrait on them (cost 1p each). The pivot
rods are held on to the 12mm collimation rods by smaller bolts
Instead of using ball and socket joints to
hold the triangles I used an
idea
from the ATM mail list of using nylon bolts. These allow a few
degrees of flex without shearing
Another false start was had gluing the mirror
to the cell. This led to astigmatic or triangular stars indicative
of pinched optics. I have ended up using cork pads on the supports
and holding the mirror in place with a sling. Also note the addition
of a fan into the side of the mirror cell, another directs air onto
the back.
