GSO Mirror Cell Improvements!

[Damo636]

I cleaned the primary mirror from my 12" GSO today & while I was at it decided to make a few alterations to the mirror cell! GSO attach the mirror to the cell by using double sided sticky backed pads, three on each triangle, but with only one of the three actually attached to the mirror back. A bit of a mess really....

I have read that a mirror, unless full thickness (2"), should not be attached to the cell at all (can make a mirror astigmatic) and should be free to float on the triangles. This particular mirror is 40mm thick so I decided to make a few changes. After removing the remainder of the adhesive pads, I replaced them with cork pads to allow the mirror to sit unrestrained......

Next I had to come up with a way to insure the support triangles would stay orientated in the correct direction. For this I used a ring cut from an A4 acrylic file folder and attached it with some double sided tape to the support triangles....

Lastly I had to add some lateral support for the mirror so it wouldn't be contacting the edge of the aluminium cell. For that I used two 3mm Nylon bolts, one at 45 degrees either side of the vertical plane.....

All in all I'm pleased with the end result and if nothing else, it'll leave the mirror a whole lot easier to remove in the future!

[Moonshane]

top modding Damo - I agree with your logic completely!

[Mike73]

Great stuff Damo.

[Daniel-K]

great stuff, gave me a good idea for the 16inch mirror cell i need to make up

[Damo636]

Cheers guys! Before assembling the scope I thought I'd check the position of the mirror center spot & found it to be off center by approx 1mm in one direction. I had a fair idea this would be the case, as no matter how well I collimated with tools, it always required a slight tweak by star test. I didn't bother rectifying it this time, but at the next annual clean I'll probably remove the existing spot and replace it with one of those triangular catseye jobs :-)

[John]

Nice work Damo

I can recall my Meade LB having the same mirror cell - when I came to remove the mirror for washing I found that all 9 of the pads were firmly stuck to the mirror back !. After quite a faff to remove them I went for the "loose" mounting option too when I put the mirror back in the cell.

Good idea to use that acrylic ring to keep the support triangles in shape

[laser_jock99]

Cheers guys! Before assembling the scope I thought I'd check the position of the mirror center spot & found it to be off center by approx 1mm in one direction. I had a fair idea this would be the case, as no matter how well I collimated with tools, it always required a slight tweak by star test. I didn't bother rectifying it this time, but at the next annual clean I'll probably remove the existing spot and replace it with one of those triangular catseye jobs :-)

Seems like a common the centre spot being off. You would think after going to the trouble of manufacturing a reasonable quality mirror the manufacture would get the spot dead on? I agree about the Catseye spots that looks like quite a good collimating method.

[Damo636]

Ok, so I couldn't leave well enough alone!

Knowing that the doughnut ring was off

centre, it started to bug the hell out of me!

One Farpoint collimation kit later and all is

now as it should be

http://www.365astronomy.com/farpoint-2inch-reflective-cheshire-collimator-red-p-2161.html

[GreatAttractor]

It's great to find this thread, I'm modifying a 12" GSO cell right now. After some gentle prying and lifting I unglued the primary and inspected the cell triangles. Two are OK, but one is moving reluctantly and jerkily in its ball joint:

 

 

Can anyone suggest what to do with it? I was thinking about applying a bit of lithium grease.