Above is a picture of my 'bearing edge supports', and here is a picture of the supports mounted inside the mirrorbox. Like piano wires, they can follow the (very small) axial movements of the mirror, when it sets on the pads when going from horizon to zenit and from zenit to horizon. Why not stick to piano wires? Two reasons:
1. I like to experiment with lateral supports, looking for the best way to support the mirrors edge without visible deformation of the mirror.
2. When I collimate the primary when collimation is relatively far off, the mirror tends to 'hang' a bit in the piano wires. Pointing the scope in vertical direction lets the wires 'jump' to neutral position again, after which the collimation can be finetuned, so it's not really a big deal. But after I motorized my telescope (Mel Bartels' stepper system), pointing the scope up was a bit more work then it used to be and I decided to look for another solution.
How did I make them?
In the 15 mm (outside) diameter tubing (so not 20 mm like the picture says), fits a 12 mm outside diameter
and 10 mm inside diameter round piece of copper tubing. The copper is
glued into the square aluminium and a 10 mm threaded rod is glued into
the copper tubing. The rollerskate bearings are 22 mm outside diameter.
When the epoxy is cured and the assemblies are painted flat black, I
just take the piano wire supports out of their holder (a connector nut)
and put the bearing supports in place. A one minute job. The nut on the
threaded rod functions as a locking nut.
Rob van Vreeden, one of the memebers of my local astronomy club, also uses bearing supports, though completely different disigned, in his 16 inch tri-dob. A picture of his mirror cell is here and a closup of one of the bearings is here.
