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Old 2nd February 2011, 08:50 AM
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rich rich is offline
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Join Date: Nov 2008
Location: Shebbear, N Devon
Posts: 1,643

This is the standard wheel that is in the box from new.

Two changes that I have made, and I think I've mentioned them before. First, the small wheel is a very close fit over the two O rings, and crushes them a bit too much for my liking, making the wheel stiff to turn. It's not the action inside the scope, it's just friction of the wheel and the O rings. So I've opened up the internal diameter of the small wheel by a tiny fraction, about 0.1 to 0.2 mm, using wet and dry paper on a suitable mandrel, then polished. The O rings are still pinched but not crushed so the water-tightness is not put at risk.

Second point, the small wheel has a slot machined on the underside, and the square shaft of the focussing movement sits in this slot. There was a bit too much clearance, and the gap had been taken up by a kind of threadlock compound. I cleaned all that off and made a top hat shaped shim 0.11mm thick that sits over the square brass shaft and packs out the gap between the shaft and the slot in the wheel. Much better job, and any backlash - which there isn't - would have to be from the action rather than from a loose wheel.

0.11mm shim is quite easy to find. It's the thickness of a Cola can.

I suppose I was just being picky, looking to improve an already superb scope. I've seen scopes where the wheel has been too tight on the O rings and it's dragged them and torn them up. At one time it was a standard mod on the mark 1 big Nikko to take out one of the O rings and bin it.
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