NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: A-10 Sextant Manual
From: Douglas Denny
Date: 2009 Jun 12, 00:52 -0700
From: Douglas Denny
Date: 2009 Jun 12, 00:52 -0700
Bill Morris: I was in error referring to a washer at the lower bearing - as I thought at first on disassembly, stuck to the bearing boss - but is the bearing itself which is a press fit into the boss. And on reflection admit the bearing should be adequate for location and positional accuracy providing the shaft does indeed press fully into the bearing due to the springs. Any friction in the shaft in its bearings mitigates against this. A proper thrust bearing would not go amiss as a proper job to reduce friction here, but the loading is so slight it is hardly necessary on second thoughts providing the whole shaft is clean, oiled and free. It was not perfectly so, with some 'stickage' - not surprising after 60 years, but even when cleaned and re-assembled the problem persists. I am now baffled, as having cleaned and re-assembled with a slightly stronger spring to ensure good location of the whole assembly on rotation of the worm the "backlash" problem is still there with a vengeance. I can only conclude that the very slight leeway in the shaft end-float is the problem still, being completely convinced (though not proven) the sector to worm gear is adequate; and that friction of the gearing from the adjustment knob through the helical gear to the worm shaft keeps the shaft slighty one way, then the other depending on the direction of rotation. I conclude it is an inherent fault consequent of the design of the gearing mechanism itself, probebly due to the high friction of the helical gear (transfering motion to the marking disc) - and is very frustrating. Attention finally moves to the counter mechanism, but that appears to be direct gearing to the first dial (seconds) and does not give the impression backlash would be present here. It is annoying I have not been able to cure the problem. Any further ideas are welcome. Douglas Denny. Chichester. England. P.S. If you wish to converse in more detail which as you say is not strictly of navigational interest here, my e-mail address is: douglas.denny@btopenworld.com --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---