Re: [ATM] A little scope for my Dad :)

["Andreas Derwahl" <andreas@duda-derwahl.de>]

Hi again,

thanks for posting the additional pictures.

> >Can you adjust the drag on the alt bearings?
>
> Yes, it works very much like the drag adjustment on a fishing pole.  By
> tightening the external nut on the alt bearing, it applies more pressure
to the
> delrin friction disk.  Works very well until the Alt bearing starts to
rotate in
> the rocker box saddle (see things I should have done #2 above)

I am not familiar with delrin friction disks, is that a brand name or some
kind of clutch system or just the name of the plastic used?

> I can't seem to find the web-page / image.  Is it actually this link?
> http://www.duda-derwahl.de/ATM/aluscope2.jpg
>

Ooops, it sure is! A typo, sorry, but I see it cannot keep a clever man from
getting to the right place  :-) .

> My aluminum on delrin alt bearings seemed to work out pretty good.  They
are
> adjustable from very little stiction, to so much that its nearly
impossible to
> move in Alt.  In both cases, once the static friction was overcome, the
kinetic
> friction was very smooth.  However, I may have just gotten lucky...

I have read a lot on the net, that the key to good tracking performance of a
Dobsonian is very little difference between static and dynamic friction.
Your comment sounds a bit like there could be a problem with this system in
higher power observations. Is such a design is prone to overshooting?

Thanks for your comments and clear skies,

Andreas Derwahl


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