2" shaft mounting Pt.49: Counterweight retaining bush.

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While I was on the lathe I turned a hefty, brass, counterweight retaining bush for the end of the declination shaft. However, it would require rather long screws on typical plastic tightening knobs. Unless, of course, I add a wide spacer to ensure finger clearance. Or used hex socket head screws which can be tightened with a hex wrench. Having struggled with hex wrenches on the Fullerscopes MkIV weight retaining bushes over the years I am not very keen. It can be critical to get the clamp on and tightened before one's strength fails and all the counterweights slide off onto one's feet! Which is why I would much prefer tool-free tightening and free-fitting weights and clamping bushes. It was always a struggle to remove the MkIV's shaft clamping bushes.

Simple thumb screws were used on the Fullerscope MkIII mounting bushes. They attracted rust like a magnet due to to both components being made of steel. Wing screws need only a little clearance for the fingers but aren't normal stock items in most DIY outlets. So the search begins again. I could use normal, plated, wing nuts and thread lock a stud into them. They would rust too unless I can obtain stainless steel wing nuts. I can feel another search coming on unless I buy them online.

As a temporary measure I drilled and tapped the bush at 120° intervals anyway. Three radial screws seemed like a better option than the usual one. Then I used plated steel M8 screws and wing nuts. The socket head screws needed the undersides of their heads tapered in the lathe to fit inside ordinary wing nuts. This gave the option of finger tight or hex wrench for extra grip, while still looking quite smart. Now I have had some practice I shall buy stainless steel screws and wing nuts in the same size for a more permanent [non-rusting] job.

Wing nuts provide plenty of torque so there is no hurry to get out the wrench to retain the counterweight. Though I would want to be absolutely certain the weights would stay in place when the declination shaft is vertical! I can see the good sense in radial drilling posher counterweights for individual screw locking. This would not be possible with my cheapo dished 'bodybuilder's' counterweights. I may need to dimple the shaft with a drill to provide extra security for the weight retaining bush screws. First I need to know how many and where the weights will be normally positioned to balance the OTA. An A-frame prop would aid weight fitting and removal.

To complete the day's efforts I drilled out all six altitude pivot holes to 16mm. A painless exercise using the lathe in back gear, the drill in the 3-jaw chuck and the tailstock providing the necessary pressure. Trying to drill large holes in under-powered, DeWalt rechargeable drills, or cheapo bench drills, is a complete waste of time and effort. The speed is far too high so they chatter and grab because there isn't enough pressure even if you lean on them.

Click on any image for an enlargement.

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