Re: [ATM] Focuser speed reducer

["Don Clement" <don_clement@charter.net>]

There is no reason a Crayford  can't also use a single leadscrew without
resorting to additional geared or similar type reducing mechanisms. In fact
I have just such a design that combines the basic Crayford with a single
zero backlash leadscrew. Also no focus locks are needed with this modified
Crayford design. But the modified Crayford design still has stiction with
it's roller/slider bearings and is not nearly as smooth as my compliant
zero-stiction focuser.

I received this e-mail from Dave Erickson about a my moving mirror
Bellerophon focuser that supports a 10" conical mirror in his 8.2" F2.6
astrograph:

" As a side note the F/2.6 has been operational for almost 2 years without
requiring collimation!  This is a testament to the stability of your focuser
and my structure..."

BTW, Dave collimates his astrograph using an interferometer.


Don Clement
Running Springs, California



> Don Clement wrote:
> > I don't use or need speed reducers. Just use a single fine pitch
leadscrew
> > with zero backlash nuts.  The advantage is no backlash or play from an
added
> > gear (or similar type) reduction mechanism. There is also excellent
> > repeatability and ultra-smooth movement because the leadscrew nuts
average
> > over many threads and have a very large contact area. Of course fine
focus
> > is inherent with leadscrew focusing whereas the Crayford design has  the
> > inherent coarse focusing limitation in which a focus reduction mechanism
> > must be added for any type of fine focus. Also the contact area of the
> > Crayford is very small, a point or line contact at best so there is also
a
> > limitation on maximum load before slipping occurs.
>
> So basically, you aren't answering my question at all, but telling list
> members why they should buy your focuser over a crayford?
>
>

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