29947Re: CNC 4 inch focuser modification
- Feb 1, 2006Hi Harvey,
Date: Wed, 01 Feb 2006 12:51:58 -0000
From: "mrgrytt" <mrgrytt@...>
Subject: Re: CNC 4 inch focuser modification
Even though it's not very difficult for a person to 'do it
themself' it's a scary thing to recommend, particularly if they don't
feel comfortable about it. I wouldn't want to see anyone take a
chance of hurting their scope.
[WG: ] I've been looking into doing this as well to my own 152 for a
few years now, as sometimes my rotating section can go from turning very
easy and smooth to being suddenly jammed up so tight that no effort at
forward movement helps and I end up knocking the whole scope out of
position and losing the object trying to get it loose again.
I always intend to look into the matter 'later' but end up putting the
scope away and forgetting about it until the next time I take it out!
Obviously, it would seem that the heart of the problem is that there is
nothing other than the three set screws riding in the channel which both
hold and guide the rotating sleeve in its motions.
But I also hope/think it very likely that if I follow Thomas' adjustment
procedures recently published (thanks Tom), this will probably either
greatly ameliorate or even largely eliminate the problem to any
reasonable extent, which I will try some day soon when I get the chance.
But there is still the likelihood of the problem returning again later I
fear. The key is in taking the weight off of the groove walls and
eliminating the friction between them and the screws (which your
However, as I do my own machining, I will be eventually settling on some
solution of my own choosing--- I suspect there is more than one way to
address the issue, and correct the deficiency so as to entirely
eliminate it from coming back again and further improving the smoothness
and stability of the rotating collar, which is imminently superb when it
is working well.
To be honest, my own ideas to this problem have been to take an entirely
different approach to the one that you and Tim have chosen, but we
shall see once I have the parts all apart in my hands what I will
In the meantime, as to your comments above, what I would ask and propose
here is for maybe you, Tim, or some other enterprising and magnanimous
person to put together a detailed description and drawings/photos of the
disassembly, reassembly, and any other pertinent points, obstacles or
hurdles for anyone undertaking such an improvement/modification of their
focuser to follow, and maybe put it in the files section for all of us
to refer to?
I've looked at Tim's pictures of the parts, both privately as well as
those recently published here, but they always leave me some questions
as to what the issues were in taking it apart. Mechanically inclined as
I am, I would feel better (as I think many would who are considering
this) knowing exactly what they are getting into before taking a very
expensive product like this apart. I think it is the time now for a
detailed and thorough article on addressing this matter safely and with
minimal risk, much like many others have published articles on taking
apart corrector plates on SCTs and fixing loose primaries, mirror flop
and focus shift. The fact that you say above that the procedure is not
very difficult tells me that it is really quite simple once you see how
the scope is put together, which obviously was designed to be very
robust, as all TMB products have been!
Can I compel you to be our volunteer to create such a document for us?
:-) You wouldn't be recommending anything, just giving us the dry facts
of what is involved and a roadmap based on your own knowledge and
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