NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: "Lost Motion" Question
From: Bill B
Date: 2006 Jul 17, 20:43 -0500
George
> But wouldn't any backlash (i.e. any lag in the body moving up or down
> when turning the micrometer dial in the opposite direction) be
> immediately apparent to the person taking the sight? Both of mine seem
> to start moving immediately when I do that, but maybe there really is
> some subtle lost motion happening there that isn't obvious to the
> observer?
I think and gear slop might show up in a slight twiddle. Assume for the
sake of argument there is none. There is also bearing play, or the restraint
that keeps the worm gear itself from moving fore and aft. Assuming that
bearing play is more resistant to pressure than gear slop (not a safe bet,
just a what if) it would take more pressure, maybe enough to rotate the worm
gear, before it would come into play.
In a deliberate set of sun off and on the arc this afternoon, I took the
precaution of moving the drum at least 30' clockwise and then anticlockwise
(bringing the reflected image down) instead of the usual 5-10 minutes
twiddle. In 12 observations each on and off the arc, it *seems* to have
increased my sigma over the small twiddle method. I say *seems* as this was
one set, one day, and my abilities to see precisely (at least as recorded
from observations) can differ from day-to-day or hour-to-hour, or even
minute to minute.
Bill
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From: Bill B
Date: 2006 Jul 17, 20:43 -0500
George
> But wouldn't any backlash (i.e. any lag in the body moving up or down
> when turning the micrometer dial in the opposite direction) be
> immediately apparent to the person taking the sight? Both of mine seem
> to start moving immediately when I do that, but maybe there really is
> some subtle lost motion happening there that isn't obvious to the
> observer?
I think and gear slop might show up in a slight twiddle. Assume for the
sake of argument there is none. There is also bearing play, or the restraint
that keeps the worm gear itself from moving fore and aft. Assuming that
bearing play is more resistant to pressure than gear slop (not a safe bet,
just a what if) it would take more pressure, maybe enough to rotate the worm
gear, before it would come into play.
In a deliberate set of sun off and on the arc this afternoon, I took the
precaution of moving the drum at least 30' clockwise and then anticlockwise
(bringing the reflected image down) instead of the usual 5-10 minutes
twiddle. In 12 observations each on and off the arc, it *seems* to have
increased my sigma over the small twiddle method. I say *seems* as this was
one set, one day, and my abilities to see precisely (at least as recorded
from observations) can differ from day-to-day or hour-to-hour, or even
minute to minute.
Bill
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
