From wpk@saao.ac.zaTue Aug 11 10:32:58 1998
Date: Thu, 30 Jul 1998 09:56:07 +0200 (GMT+0200)
From: Willie Koorts <wpk@saao.ac.za>
To: Paulina Fernandez & Eduardo Perez <pfernan@rdc.cl>
Subject: Re: Your telescope mount


On Wed, 29 Jul 1998, Paulina Fernandez & Eduardo Perez wrote:

> Dear Willie,
> 
> I seen your scope mount WWW and looks quite good. I Starting with my plans
> to build an EQ mount for my 8" DOB some weeks ago and Im quite intrigued
> about your design.

Hi Eduardo

Thanks for the nice comments.

> My goal is use the mount for astrophotos. 
> 
> 1.- I would like to know if you are using this mount for that purposes or
>     only for eye view tracking

So far I have not tried any astrophotography with the scope and thus was 
only used visually.  The main reason being that my drive is not actually fine
enough.  As I explained to Anthony Davoli (see my telescope FAQ page), the
present gearing translates into 3.3 seconds of arc movement of the telescope
per step of the stepper motor.  This should be about 1 arc sec/step or better
(I seem to recall reading somewhere some time) to be good enough for
photography. This you will also have to keep in mind when designing your
drive chain gearing if you want to use a stepper motor. 

> 2.- Some sugestion about the kind of panelboard used and the thickness to
>     do not have deformations problems?

To make the split-ring, I used plywood originally used as a shipping crate. 
The wood looked like fair quality but is not the best I have seen before, but
not the worst either.  This was 12mm thick (1/2") which I doubled up by
glueing two layers together yielding an effective 24mm (~1") ply. For the
telescope box I used 9mm marine ply also doubled up giving an effective 
18mm (3/4") ply. 

As far as deformation goes, nothing that I could really notice.  The weakest
point is probably the split-ring where there is only 70mm left at the end of
the split.  This is solved by making the telescope a good fit (sideways) into
the split - that's why I also cladded the sides of the DEC rings with Formica
which push against teflon pads on the mount.  Another possible source of
deformation is the foldable ring itself being forced open at the hinges by
the telescope's weight.  This is prevented by the two aluminium brackets
forming triangles and which are positioned such that they also touch the 
DEC rings, counteracting this force. 

> Thanks in advance and best regards,
> 
> Eduardo Perez
> Forest Engineer
> Santiago - Chile

You're welcome.  Happy ATMing.

Regards
Willie
                        Willie Koorts   wpk@saao.ac.za   

       Cape Town,  Observatory   33d 56' 03"S   18d 28' 36"E   GMT + 2h
       Wellington, South Africa  33d 38' 56"S   19d 00' 52"E   GMT + 2h

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