52 replies to this topic

[apfever]

OK, so you drilled out the center of the holder so the main bolt could pass through and take an acorn inside?  No clearance concerns or special short acorn to clear the glass?  The acorn nut would be a full threaded bore so it can go on 'backwards'?    I LIKE this. I'd still use allen head cap screws for collimation so I can rest the allens in place and have simultaneous adjustment on two screws.  The larger collimation screws can be rounded or pointed on the end so they nest in the original holes in the holder. Nesting the screws would keep them from walking the holder around when they are turned. 

 

The ones I'm working on are all different on how the center bolt is attached. They all have the set screw but one has one nut as you described, one has two nuts with one on each side of the spider hub, and one had no nuts - only the set screw. They all looked original with factory finish over them. One nut had a star lock washer. Typical variations that might have changed daily or even the same day!

 

Nice idea but I'm going more original and avoid the drilling and tapping. deSitter's work is well thought out and part of my decision to stay original is to simply offer another idea. I will get the allen bolts. I'll leave out the main bolt set screw - Yep, bad idea - and lock the bolt with a nut tightened to the hub.  

 

Original is not the best design for sure but not horrible, not the worst by far. The vane hub could have been larger and used as the back plate, with the mirror holder moved much closer to the hub. Hindsight. 

[deSitter]

OK, so you drilled out the center of the holder so the main bolt could pass through and take an acorn inside?  No clearance concerns or special short acorn to clear the glass?  The acorn nut would be a full threaded bore so it can go on 'backwards'?    I LIKE this. I'd still use allen head cap screws for collimation so I can rest the allens in place and have simultaneous adjustment on two screws.  The larger collimation screws can be rounded or pointed on the end so they nest in the original holes in the holder. Nesting the screws would keep them from walking the holder around when they are turned. 

 

The ones I'm working on are all different on how the center bolt is attached. They all have the set screw but one has one nut as you described, one has two nuts with one on each side of the spider hub, and one had no nuts - only the set screw. They all looked original with factory finish over them. One nut had a star lock washer. Typical variations that might have changed daily or even the same day!

 

Nice idea but I'm going more original and avoid the drilling and tapping. deSitter's work is well thought out and part of my decision to stay original is to simply offer another idea. I will get the allen bolts. I'll leave out the main bolt set screw - Yep, bad idea - and lock the bolt with a nut tightened to the hub.  

 

Original is not the best design for sure but not horrible, not the worst by far. The vane hub could have been larger and used as the back plate, with the mirror holder moved much closer to the hub. Hindsight. 

The key point of my rebuild was to make dimples in the cell plate so the pushers can push and not wander. I filed down the ends like a pencil and they went into the dimple and pushed. The tiniest adjustment of the pushers caused a visible change in collimation. I also remember thinking I needed 10-28 screws for a finer adjustment but didn't have a tap for that Ah the fun of homebrew engineering! If I could make money on spiders, I would be making them today!

 

-drl

[mfoose]

I'm still thinking about what to do for the secondary mirror holder. I may end up just keeping it as is and putting a nut to act as a stop on the collimation bolt that could damage the mirror. That way it would stop before any potential damage and I would simply loosen the two other collimation bolts and try for collimation again. I don't love the design, but I don't want to spend too much time on it if it holds collimation fine as is. 

 

With the spider removed, I cleaned the tube today. Any tips on how to straighten the spider vanes after it's put back in?

 

I also worked on the focuser today. It cleaned up easy and the brass came out looking nice. Time to re-install.