mirror cell

[ponytale]

hi all, just thought i would post pics of my mirror cell update ,

the cell is birch ply 24mm with alloy strip ring fixed to edge with 3 places for mirror clips @ 120degree , i decided to try the centre pivot method as i did not have suitable springs to hand, the yellow ball in the centre is hard nylon drilled and threaded onto a stud in the centre this is the pivot on top of the ball is an old router plate that happenned to have a pressed out dished hole in the centre that is the right size , i was going to fix the plate but realized it was a bit easier to adjust with a slideing plate as the adjustments are made the plate moves a tiny amount so there must be slight lateral forces at work i guess ? i found the adjusting very easy a little tighten one way and a equal release the other in small steps seems to be very precise and the mirror plate is very secure and doesn't move afterwards i used a spanner tu adjust but i will fit hole through type knobs soon, the yellow knobs are there temporarily just to stop skin damage to me and thread damage . The mirror is finished but not coated yet as i wanted to assemble and weigh the cell ( 5 kg) so i can substitute the mirror with weights while i do other work on the mount hope this of interest to someone , any comments welcome

[Moonshane]

very timely Tony and a great job so far. I have started work on mine and will be make a very similar design albeit with more structure given it's a 16" mirror.

see the bottom of here http://stargazerslounge.com/diy-astronomer/140533-16-f4-orion-optics-uk-dobsonian-project-2.html where I have made a start.

how are you fixing yours to the tube?

[ponytale]

hi moonshane , i have 3x 6mm woodserts in sides at 120 degrees spacing , i have strayed from my original adustable dob through a trunnion bearing box setup ( too Heavy )to a lighter more portable adjustable 4 tube design in a rocker box at the mirror end, as per attached drawing, as the tube length is adjustable and i will have made 2 mirrors of differing focal lengths i want to be able to swap mirror cells via 3 quick release index bolts,then adjust tubes length to a pre set position which locks then a quick recollimate ,

as the cell is round i can probably drill 3 more 120 degree holes for the index bolts later on when things are more advanced.

truss dob2.doc