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After mounting my Sky-Watcher short-tube achromatic
refractor atop the LX90, the entire balance of the scope needed
reconfiguration along two dimensions. My existing Meade weight set was
insufficient for this task because it is one-dimensional and only
permits balance within the horizontal axis. Because the centre of
gravity shifts upward after mounting the short-tube, equal weight needs
to be added at a similar distance below the LX90 in order to balance the
scope along the vertical axis also.
The most
popular option to solve this type of balance problem is to purchase the
Losmandy weight
and dovetail plate system, and many amateur astronomers have done just
that. Rather than pay several hundred Australian dollars for something I
felt I could make myself, I started searching for a solution on the net
and came upon the work of Janet Miller. Jan had a very similar setup to
my own and her solution was to modify the Meade weight system to enable
it to balance her scope in two dimensions. My mod is very similar to
Jan's work, which you can find well documented
here.
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Procedure
This mod requires a thread being tapped into the 1-pound
weight so that either the 2 or 3-pound weight can be attached to it by
threaded rod and hung along the vertical axis. I have never tapped a
thread in my life so I sought lots of advice from the bloke ay my local
hardware store. Jan also advised caution in undertaking this mod as the
steel weights are made of very hard steel. Unperturbed in my desire to
save big pucks, I pressed on.I used imperial
stock for this mod as it was more available than metric sizes for the
rod diameter and type I was after. I chose 5/16 inch steel rod and
obtained a 5/16 inch tap for about AU$7.00 at the local hardware store.
For this sized tap, a 1/4 inch hole is to be drilled to the depth you
need, about 40mm in my case. It is critical that the hole is perfectly
perpendicular to the surface of the weight, so take your time lining
things up, or use a drill press if you have one. When using the tap,
turn only part way then retreat to snap the new steel thread, then rock
the tap back and forth along the new thread until the motion feels
smooth before proceeding further. Periodically retreat all the way out
and back in again. You will need to use a suitable oil and use lots of
it. I used fine-grade sewing machine oil, which worked very well. Take
your time and don't overstress the tap by forcing it too far each turn.
The
final
product |
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Front view
The one pound weight (left) is tapped. The two pound weight (right) is
attached through its normal attachment axis. |
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Side view
For a view of the mod
attached to the scope, click
here
(scroll to bottom of page). |
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All information and images are copyright
© 2003-2004 by P B Langsford. Please ask if you wish to use them or link
to them |
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