NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: "Lost Motion" Question
From: Greg R_
Date: 2006 Jul 17, 19:32 -0500
I'd agree with your theory except for one thing: In practice whenever I
turn the drum in the opposite direction there's absolutely *no* lag in
the celestial object moving in the opposite direction. Might have
something to do with the fact that both sextants are relatively new and
don't have a lot of wear on the teeth.
I think the best way to answer the question "scientifically" (at least
in the limited case of my 2 sextants) is to take a series of sights
with some done in the same direction, and some done "up and down" like
I mentioned earlier and compare the results.
--
GregR
--- Red <hellosailor@verizon.net> wrote:
> Greg-
> "But wouldn't any backlash ...be immediately apparent"
>
> No. Backlash is considered to be any slippage in the gearing
> mechanism. Consider this little ASCII art, if it comes over properly:
>
>
> ----U----U----U----U
> =A===A====A===A====
>
> Those are uppercase "U" and "A" meant only to illustrate a poorly
> fitting set and unevely made of gear teeth, i.e. the worn smoothed
> teeth against the newer sharper teeth, with "wear space" exagerated
> between them all. What happens if you shit the rack "A" from left to
> right? Well, it engages properly in either direction. But shift it to
> the left, and it hits the "U" teeth and engages/aligns in a different
> position from when you shift it to the right. And as the unevenly
> positioned teeth wear, that will shift a bit more too.
>
> With or without spring loading, or grease taking up slop, etc., that
> kind of "gear slop" is generally considered to be a part of the
> "backlash" problem, even if it isn't truly backlash (a force pushing
> back). So always working in the same direction (i.e. always go past
> and always come back) simply ensures the two racks (gears, screw
> threads, whatever) are meeting on the same side, which gives a more
> uniform and precise result.
>
> >
--~--~---------~--~----~------------~-------~--~----~
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To , send email to NavList-@fer3.com
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From: Greg R_
Date: 2006 Jul 17, 19:32 -0500
I'd agree with your theory except for one thing: In practice whenever I
turn the drum in the opposite direction there's absolutely *no* lag in
the celestial object moving in the opposite direction. Might have
something to do with the fact that both sextants are relatively new and
don't have a lot of wear on the teeth.
I think the best way to answer the question "scientifically" (at least
in the limited case of my 2 sextants) is to take a series of sights
with some done in the same direction, and some done "up and down" like
I mentioned earlier and compare the results.
--
GregR
--- Red <hellosailor@verizon.net> wrote:
> Greg-
> "But wouldn't any backlash ...be immediately apparent"
>
> No. Backlash is considered to be any slippage in the gearing
> mechanism. Consider this little ASCII art, if it comes over properly:
>
>
> ----U----U----U----U
> =A===A====A===A====
>
> Those are uppercase "U" and "A" meant only to illustrate a poorly
> fitting set and unevely made of gear teeth, i.e. the worn smoothed
> teeth against the newer sharper teeth, with "wear space" exagerated
> between them all. What happens if you shit the rack "A" from left to
> right? Well, it engages properly in either direction. But shift it to
> the left, and it hits the "U" teeth and engages/aligns in a different
> position from when you shift it to the right. And as the unevenly
> positioned teeth wear, that will shift a bit more too.
>
> With or without spring loading, or grease taking up slop, etc., that
> kind of "gear slop" is generally considered to be a part of the
> "backlash" problem, even if it isn't truly backlash (a force pushing
> back). So always working in the same direction (i.e. always go past
> and always come back) simply ensures the two racks (gears, screw
> threads, whatever) are meeting on the same side, which gives a more
> uniform and precise result.
>
> >
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
