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 11, 04:56 -0700
From: Douglas Denny
Date: 2009 Jun 11, 04:56 -0700
Hello Bill, The worm assembly came apart very easily. I made a simple crude anvil to back-up the shaft to remove the pins (picture) it being essential to prevent any distortion of the shaft whilst driving the pins out. They came out quite easily. It is also essential to be very careful indeed to remove the shaft without touching the threads as the clearence through the upper bearing is not much. ------------ I am not impressed by the use of this method of position fixing for the shaft axially, even if used elsewhere in engineering. In this instance particularly, the bearing surface of the shaft diameter on the washer must only be a fraction of a mm creating a very small annulus of bearing on the washer, and any piece of dust/grit or other detritus getting between will cause trouble. It also has friction that should be avoided at this point which would be eliminated with a proper bearing. Also, if the washer is slightly bent or out of true and/or the shaft bearing edge not true then there will be an up and down movement on 360 degree rotation of the shaft(unless the washer travels with the shaft rotation which is unlikely with the greater friction of the washer on the bearing boss). The best practice method here should have been a small taper-roller bearing. As there is room between the helical gear onthe shaft, and the bearing boss I shall investigate the possibility of replacing the crude shaft/washer end-thrust bearing with a taper-roller beraing. It should not be too difficult to do and if I can get a bearing with internal diam the same as the shaft diam then I am home and dry - otherwise a bit of lathe work on the worm shaft is necessary. Can be done without too much trouble I reckon. -------- I have not modified the sextant in any way (yet) the ball-race bearing you see is as seen when opened. Regards, Douglas Denny. Chcihester. England. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---