Just received an Odyssey Compact. Need some help..
Posted 10 June 2011 - 06:12 PM
What I meant was two (or three) brackets with a bearing point along the side, positioned at a point midway up. If the mirror was flat, it would be at half the thickness of the mirror.
The point of the tape around the periphery of the mirror would be to restrict the movement of the mirror - just like mirror clips. And like them, the idea is to not have any force incident on the mirror in the normal operation of the scope, thus they don't distort the mirror. The normal load path is through the bearing surfaces ONLY. The clip/tape is to secure so that if inverted, the mirror doesn't fall out.
Do not recommend a tight ring around the mirror of firm material as thermal expansion might bind and buckle. Another approach is to use a edge support strap.
Do more research on cell design. You need to understand more.
I'm thinking of a low profile design (my mirror is further back in the tube, requires it) out of 3/8" square extruded aluminum in two T sections joined with collimation screws. Three bars with pivots in center and nylon pads at ends. Two outrigger brackets support the edge through a nylon bearing as a single point of contact. Tape surrounding mirror as in the original cell - that doesn't bother me.
Posted 11 June 2011 - 07:22 AM
Posted 11 June 2011 - 07:24 AM
Posted 11 June 2011 - 02:20 PM
I must say though that the original cell that came with your telescope looks like it was thoughtfully constructed.
My criticism of it would be just the "slop" and "flop" aspects in its concept of "edge support". One could also improve the ventilation as well.
Posted 11 June 2011 - 03:37 PM
@George, thanks. I actually found this the other day and proceeded to confirm that the system is working properly.
@wfj, from what I'm hearing it seems I'm going to need some guidance / directions in either dealing with this current cell or constructing a new one. Some things I understand, others I have yet to understand
Posted 12 June 2011 - 07:13 AM
A 6-point cell can be built with one trip to the hardware store. Here's picture of one that I use for my 14-inch. The mounting plate is honeycomb aluminum panel but could just as easily be wood. A little flexure in the mounting plate does not matter. Note the use of box channel (and a lot of little nuts and bolts) to build the support frame.
Posted 12 June 2011 - 09:04 AM
On another note, I just noticed on my coulter cell that the cardboard triangles used for the nine point were flexing to the point that the mirror essentially rests on the mounting posts rather than the points. Would aluminum strips eventually do the same thing with the eight pound mirror, and if so, would it be better to use square tubing like you do in your designs?
Posted 12 June 2011 - 11:01 AM
Incidentally, properly designed 6-point cells are usually superior to nine point cells for small mirrors. This is based on finite element analysis. See for example:
For my travel scopes like the 14-inch, I take the mirrors out and so do not use silicon. The 12.5-inch scope uses mirror clips that do not quite touch the mirror surface but will keep it from falling out if tilted down. This scope is permanently mounted.
Posted 21 January 2013 - 05:07 PM
Posted 22 January 2013 - 10:26 AM