NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: "Lost Motion" Question
From: George Huxtable
Date: 2006 Jul 22, 11:27 -0500
I agree with all Geoffrey Kolbe's posting about backlash except for
his final sentence, when he wrote-
|Clive Sutherland also mentioned
| the possibility of play in the tapered shaft holding the index arm
| onto the frame. The symptoms of this would be exactly the same as
| radial play in the tangent worm screw shaft.
=================
No, I think the symptoms of such looseness would be rather different,
because it occurs at the other end of the index arm. It would not
depend on whether the drum was being turned clockwise or
anti-clockwise, but it could be affected by any tilt of the
instrument, or by whether it had just been tilted, in the fore-and-aft
direction, or perhaps just according to the way the index adjustment
was being gripped. It could differ depending on whether it was the
upper part of the arc range, or the lower, that was being read. I have
never heard of such an error being apparent in practice in a sextant,
but that doesn't imply that it can't occur.
My cheap Ebbco plastic sextant has a non-tapered bearing as its index
arm pivot (plastic in plastic, polycarbonate) and I can detect no
shake there by feel. I don't know what a dial gauge would show, and
wonder whether prolonged daily use might result in wear and subsequent
looseness. At present it will be contributing little to the overall
inaccuracy.
George.
contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
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To , send email to NavList-@fer3.com
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From: George Huxtable
Date: 2006 Jul 22, 11:27 -0500
I agree with all Geoffrey Kolbe's posting about backlash except for
his final sentence, when he wrote-
|Clive Sutherland also mentioned
| the possibility of play in the tapered shaft holding the index arm
| onto the frame. The symptoms of this would be exactly the same as
| radial play in the tangent worm screw shaft.
=================
No, I think the symptoms of such looseness would be rather different,
because it occurs at the other end of the index arm. It would not
depend on whether the drum was being turned clockwise or
anti-clockwise, but it could be affected by any tilt of the
instrument, or by whether it had just been tilted, in the fore-and-aft
direction, or perhaps just according to the way the index adjustment
was being gripped. It could differ depending on whether it was the
upper part of the arc range, or the lower, that was being read. I have
never heard of such an error being apparent in practice in a sextant,
but that doesn't imply that it can't occur.
My cheap Ebbco plastic sextant has a non-tapered bearing as its index
arm pivot (plastic in plastic, polycarbonate) and I can detect no
shake there by feel. I don't know what a dial gauge would show, and
wonder whether prolonged daily use might result in wear and subsequent
looseness. At present it will be contributing little to the overall
inaccuracy.
George.
contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
