Mounting build: Counterweights and shaft locks.

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I should paint the weights white to help avoid collisions with my head in dim light. I might just have to get a longer length of 50mm stainless steel shaft to make more room for more counterweights. Fortunately it is very easy to swap shafts thanks to the Tollok clamping bushes. Apart from handling the sheer weight of the shaft itself, of course. They really are "lumpy!"

It may seem like excessive fuss over a few counterweights but I'm thinking of the future. Old age is eventually bound to take its toll. My ability to lift heavy weights to the height of the mounting is bound to reduce over time. Lifting a weight above head height requires a stepladder to lift me to my former head height.

Moreover, I never fitted shaft locks or brakes to the mounting. The clutches on the wormwheels are protective. Not intended to lock the shafts against severe imbalances. Loose weights on a bare shaft waiting for the locking ring, could easily cause it to tip downwards. With catastrophic results. The damage to the floor and ladder from three 5kg steel disks falling from such a height would not be light. This assumes they miss me as I teeter high on the ladder.

I once tried using a slot in the end of a length of timber to support the shaft while I loaded the counterweights. Though this is not completely safe unless the timber prop is securely located and the bottom resting on a firm surface. Not to mention the prop being of exactly the correct length/height.

What happens when the weights want to be in the same place as the timber prop? When there is no more room for more weights and the locking collar? With such large and heavy weights [and heavy instruments ] it doesn't take much of an imbalance. The whole assembly can rotate viciously when released. I could screw a sturdy metal plate with the slot to the prop instead of having 2" thick timber using up vital shaft space. 

If I let the weights swing downwards I can't reach the raised cradle with the large and heavy telescope!

So I really need secure shaft locks. Not simple screwed rods pressing onto the shafts. That would mar the shafts and make shaft removal through vital components impossible.

Ideally it needs really solid, split block clamps to provide enough pressure from comfortable hand wheels working on ample diameters of stainless steel screwed rod/studding. The split blocks need to be securely located against all rotational movement and a close fit on the shafts.

Excessive precision requirements should be designed out first. While still making the clamps completely fail-safe in use. And, without requiring excessive hand pressure on the hand-wheels. That means ample leverage on the splits by moving the actuating studs well away from the shafts.

The contact/braking/locking surfaces of the clamps must be able to be spun in the lathe. For accuracy in hole sizing and position. A cylindrical furniture 'nut' sitting in a cross drilled hole will avoid deep thread cutting for the actuating stud.

A much simpler idea would be a half circle clamp hinged on a fixed bolt. The bolt becomes the only necessary location point for the clamp. A cylindrical nut in a cross-drilled hole avoids making deep threads in the clamp body which would always be subject to side forces.

The entire clamp can be lost inside the bearing housings. With only the hand-wheel visible on the outside.

Two strips of aluminium could be used with a small separation between them for the tension stud. This would allow the hinge bolt to become an eye bolt sitting between the two strips. The eye bolt would only be subject to compression forces.

A 50mm hole saw can be used to make the half circles. Perhaps clamping two sets of strips together to provide a symmetrical and simultaneous drilling operation.  The eye bolt can be planted once the half circle of the clamping strips are closely located around the shaft. Thereby avoiding the need for high precision in their location. Even asymmetrical pressure over the area of [half of] a 50mm shaft should be enough to hold it absolutely firm.

There was s little room inside the polar bearing housing I decided to go for something even simpler. I bored a cylinder of brass to make a close fitting sleeve for the polar shaft. Then threaded the top plate M8 for a small hand-wheel. The end of the hand-wheel stud was reduced to fit a 6mm hole in the brass sleeve. The hope is that the brass sleeve will provide a lock without the hand-wheel stud coming into direct contact with the shaft. If the threaded rod on the hand-wheel tries to bend sideways I shall have to provide a supporting plate inside the polar bearing housing. Just to stop lateral movement.

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