Re: Spoke based spiders (was Re: ATM Wiring Spiders)

["Jeff Anderson-Lee" <jandersonlee@sbcglobal.net>]

It sounds like an interesting design.  I might suggest though that
you try to avoid having the secondary holder wider that the
secondary mirror, so either make the second pipe smaller
than the first and fit inside it, or make the pipe that attaches to
the mirror of smaller diameter so that the outer one is still
under 1" in outer diameter.  That will help minimize the obstruction.
There should be no problem in gluing the secondary to a smaller
diameter pipe.  In fact, most primary mirrors are supported by
points inside the radius.

I do notice your setup has no adjustment for tilting the secondary.
You might possibly get enough play from the bicycle spokes
to make that adjustment, but do allow yourself some means to
make that adjustment too.

Jeff Anderson-Lee

----- Original Message -----
From: <k_patel@vsnl.com>
Cc: <atm@shore.net>
Sent: Friday, February 15, 2002 7:47 AM
Subject: Spoke based spiders (was Re: ATM Wiring Spiders)


>
> Hello, all,
>
> Spiders is where my telescope is at, at the moment.
>
> The 6" mirror I was polishing has come back after being aluminized,
and
> to my biased, subjective, eye, it looks beautiful. To my unbiased,
> objective, eye, the outermost half-inch is definitely unfinished, and
> needed an hour or two of extra work on the pitch lap. But I started
> grinding in May, last year, and the family was starting to wonder if,
> not when, it would be finished.
>
> So now I am making the spider, which is being planned as follows:
> The diagonal mirror, whose minor axis is 1" in dia,  will be stuck to
a
> PVC pipe, also 1" in dia, whose end has been cut at 45 degrees and
> smoothened flat. This will be inserted into another, larger pipe,
which
> will be suspended with the help of bicycle spokes. The spokes, each
2mm
> thick, will be inserted through this larger pipe, and their ends will
be
> attached to the frame by wooden clamps. The small pipe slides
smoothely
> in the larger one and a tiny screw will fix it in position once
aligned.
>
> This arrangement will allow the diagonal mirror to be rotated as well
as
> moved towards and away from the main mirror. By suitably positioning
the
> ends of the spokes before clamping it will be possible to position the
> diagonal perpendicularly to the main mirror as well. Once collimated,
> small adjustments to the main mirror (with the help of its own
alignment
> screws) should suffice to maintain alignment.
>
> Advice on the finer points of spoke based spiders and other comments
> from the list will be gratefully received.
>
> Sincerely,
> Kartik Patel
> Bombay, India
> k_patel@vsnl.com
>
>
>