Re: [ATM] Steel tubing for mirror cell

["matt" <electro_optic@bellsouth.net>]

for lower mirror edge support, use 4 pins, paired , each at the ends of 2
bars.
The bars should pivot at the middle, just like a 6 point cell (only the 6
point cell would have 3 such bars with 3 pairs of support points, and you
would only have 2 bars with 4 supports ).
Place the bar pivots at the corners between your vertical and horizontal 1"
extrusions , that'd be the most rigid placement.

best regards,
matt tudor


-----Original Message-----
From: Alan K. Henderson <alankh@ev1.net>
To: atm@atmlist.net <atm@atmlist.net>
Date: Wednesday, February 23, 2005 1:39 PM
Subject: [ATM] Steel tubing for mirror cell


Here is my rough draft for the mirror cell. Image is to scale. (Upper
portion not designed yet - saving the easiest part for last.)

http://users3.ev1.net/~alankh/CellDraft.gif

The design assumes 1" extrusion for the cell frame, 1/4" bolts for the
triangles (not shown), 1/2" collimation bolts, and two lower support pins
made from 1/2" bolts and 1.5" nylon cylinders (and 3.5" long). As you can
see, I had already decided to separate the collimation bolts from the mirror
support. My first concern about this design is whether 1" tubing is wide
enough for drilling a half-inch hole without a structural integrity problem.
I'm confident about the bolt thickness; K&B say they'll support a 30"
mirror, which tends to weigh quite a bit more than 50 lbs.

My biggest concern is the lower mirror support. The pins must support 50
pounds. They are currently set 50 degrees apart from each other. The
horizontal extrusion between the pins prevents the downward force of the
mirror (when pointed at horizon) from pushing the pins away from each other.
I doubt that the current design is sturdy enough, but there are several ways
that they could be reinforced. There's room to add two extra support pins,
but figuring out how to evenly balance the load between four pins would be
difficult.

Alan K. Henderson
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