Re: [ATM] 16in tridob rebuild 1st light (long)

[Dave Smith <smithersscope@yahoo.com>]

--- Jan van Gastel <jhm.vangastel@wanadoo.nl> wrote:

> I like the ball-socket joints for the trusses. It
> cost me lots of time and 
> frustration to get the angles right and still the
> secondary is not exactly 
> centered above the primary. Maybe I will go for the
> ball-socket method as 
> well when I have time.

The ball & socket clamps work REALLY well. I'll get a
better idea of how well they hold up and how close (or
repeatable) collimation is based on continued
assembly/reassembly. So far though, I'm very pleased
with them. They are also VERY easy to construct...a
block of solid wood with four holes, two of which are
tapped & threaded. The balls I purchased from the
art/craft store had a small flat surface on one side
where I drilled and epoxied in a short section of
wooden dowel to connect to/insert into each truss
tube.
 
> I have a question about your new focuser. You say,
> that one bearing support 
> works better then two? Could you please explain?


You bet, Jan!
First, so everyone's on the same page, here's a link
to an image of the original focuser.
http://dsmith.no-ip.org/smithersscope/images/focuser_01_sm.jpg

and here's a link to the solidworks images of the fix:
http://dsmith.no-ip.org/smithersscope/atm/solidworks.htm
(scroll down about 3/4 of the page)


In the original version of the Crayford I had two
pieces of nylon driven by two nylon thumbscrews that
applied adjustable force to the focuser shaft and
focuser draw tube. Depending on how much weight I had
in the draw tube (i.e. +/- heavy barlow) I found
myself constantly tweaking the tension on the
thumbscrews. A couple of times one of the little
pieces of nylon fell out. Very annoying. Dangerous if
the focuser fell apart while viewing! So while
thinking of a fix, I realized I only needed one piece
of material rather than two. I happened to be in East
Texas at Christmas when this happened to my brother's
8" Newt (I had given him my original focuser.) My dad
didn't have any nylon, so we used some weird synthetic
plastic (Delrin?) as a quick fix. We took an 8 inch
stick of this plastic (about 1/2 inch thick and 2
inches wide) and drilled a hole through the 2 inch
dimension with a bit the same size as the focuser
shaft about 1/2 inch from the end. Then we used a
table saw to rip across the 2 inch width right down
the middle of the hole we had drilled. This left us
with two 2 inch long pieces of plastic with grooves
lengthwise that fit perfectly between the focuser
shaft and the two thumbscrews. (only needed one; why
did I leave the extra in one in Texas? Doh!). We then
drilled divits into the backside (opposite the shaft
groove) to keep the piece centered on the thumbscrews.
It worked better than we expected. It's very smooth
and will probably never wear out.
After I got home I replaced the nylon studs on mine as
well. I didn't have any slick plastic, so I used a
piece of mahogany. It works great also, believe it or
not, without any lubrication.
If anyone has more questions, or if the description
and pics aren't clear enough, just holler.
It's an easy fix and requires no complicated
tooling...a drill and a handsaw would do the job.

Good luck!
Dave


       
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