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I put a Crayford from Andrews onto my 8 inch a few months ago. The focusing is much smother now and one turn of the Crayford produces about half the tube movement as the old R&P that came with it. The mounting flange that came with it was exactly the right size for my tube, which saved a lot of work. However, I was not happy with how the focusing mechanism is attached to the flange - two grub screws on either side of a shoulder. I have subsequently machined (having a lathe in the garage is handy) a ring to attatch the two parts together with several screws, as a result you could hang a car or Nagler off it (whichever is the heavier!).
I have also attached a small geared electric motor to the shaft and a couple of batteries etc. for a total cost of about $20.
the main problem I have found with the focuser is that sometimes it slips, and won't move the focus tube up or down (depending on which direction it is facing). I may need to do some more work on it some time, but at the moment it works great! No shaking, and easy to adjust.
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