Mounting: Drive imrovements and folded refractor alignment.

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In my continuing struggle with Slew/Goto motor stalls I removed the RA motor and worm assembly. First I made a brass tension roller in the lathe to replace the brass sleeved, rubber one. Then put the motor back on the mounting. Better, but still occasional motor stalls.

So I took it all off again and withdrew the worm to allow the larger timing pulley to be removed. This is a far easier method than trying to lever the pulley off the worm shaft with the tensioned belt still in place.

A washer was added as a shim behind the pulley and the drive rebuilt and replaced yet again. The motor now ran for much longer before a noisy stall occurred. The OTA and mounting  balance now seems about as good as I can manage. Friction seems adequately low. I'll have to check the height of the worm against the wormwheel again though it seems okay.

There followed an extended session of folded refractor collimation. At first I had the springs fully tightened on the extended mirror cell supports. So I added more packing to the third [fixed but flexible] points of the enlarged triangles. This gave me the freedom to collimate the folding mirrors without compressing the springs so much.

I plan to extend the collimation screws for the second, smaller mirror cell to have adjusters directly on the backplate. The present wing nuts are just beyond comfortable reach. Meaning that I cannot actually look through the open focuser while I collimate. Which greatly slows down collimation. I'll probably use threaded inserts in stainless steel tubes as extenders. I just need to find some smart and comfortable adjusting knobs to go on the backplate.

A visit to a builder's merchant provided a small collection of smart, black plastic furniture 'feet' with potential as collimation adjustment knobs. Matching the threads to a dwindling collection of expansion 'nuts' is proving more difficult. I may be able to turn some hex nuts to fit tightly in the tubing I planned to use. There is also the possibility of cutting fresh threads directly in the tubes [or an adapter] with a tap. Thread locking fluid could be useful here.

Interestingly [?] I discovered that the edges of the OTA frame do not agree with the optical [axis] alignment. It is no wonder I couldn't find Mars by sighting along the frame! I'll have to look into this misalignment because I have no idea why it should be like this. Or whether it is important to image quality. There was an error of about 6' from the optical viewpoint compared with sighting along the corner of the OTA frame when using a 32mm EP. This was using a target at about 175 yards @ 67.5x with a 2160mm focal length.

Click on any image for an enlargement.

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