NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Visit to Freiberg
From: Courtney Thomas
Date: 2005 May 23, 17:02 -0500
From: Courtney Thomas
Date: 2005 May 23, 17:02 -0500
Bill, Thanks for your replies. I somehow missed the earlier post to which you refer concerning "power lines". Could you relay a copy please ? Cordially, Courtney On Mon, 2005-05-23 at 15:18, Bill wrote: > > What is backlash ? > > Courtney > > Any "slop" in the gears. If something is machined for a "press fit" you will > need and arbor press or some other method the fit one part inside the other. > Gears would wear rather quickly and be very hard to turn. If the part > sliding in is machined smaller than the opening it goes into for a sliding > fit, there will be some slack/slop. The easier they slide together, the > greater the slop. > > > > Without going to Germany, how do you know if it's a problem with your > > sextant ? > > I suggest power lines (see earlier post). > > > > Can you [yourself] approximately 'measure' it's significance with your > > sextant and correlate turning said 'screw', recheck and approximate a > > satisfactory adjustment ? > > Would have to see a SNO-T again to know how it is set up. My table saw for > example, gives the operator the ability to move the blade-angle-adjustment > gears closer together to reduce backlash and compensate for wear. It will > stay where set. My Astra IIIB, according to Celestaire, uses a spring to > apply pressure on the worm gear to hold it against the arc teeth. > > The plus side of a spring is that the pressure of the worm gear against the > arc will remain almost constant along the arc, even if the arc is not > perfect. IF the screw on the SNO-T regulates a spring pressure, the same > would apply. > > IF the screw on the SNO-T fixes the worm gear in a given position (like my > table saw) then the backlash will vary along the arc unless the arc is > perfectly equidistant from and tangent to the pivot point of the arm. > > My Astra appears to use a brass worm gear, so it will probably (slightly) > self lubricate against brass or a hard aluminum alloy arc. It may also wear > faster than the body. But easier to replace a worm gear than the sextant > body/arc. > > In either case the tradeoff for reducing backlash is increased gear wear and > increased effort to turn the drum. Which points out the need for keeping > the gears clean and lightly lubricated. > > Bill