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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
