GSO make a great Crayford style focuser that is quite a nice piece of engineering but mine seems to be let down by having quite a large amount of tilt on the main drawtube.
When imaging with my QHY-8 this shows up as annoying elongated stars, emphasised by the short focal length 12" F5 Newt.
I measured this tilt with my digital verniers and it was almost a whole millimetre out.
(Pic 2)
I pulled the focuser apart to see if I could minimise or eliminate this tilt.
Firstly I removed the 1:1 knurled focuser wheel with a 4mm allen key. I also removed the two knobs on the underside, being careful to remember which threaded holes they came from. They are different lengths and have different functions each, as
Pic 3 shows. The longer is the Lock Screw and the shorter is the tensioning/ grip screw.
Removing these allows the remaining shaft and 10:1 assembly to come out to the right.
Pic 4 shows this and also shows the small black bush which I was careful not to lose!
The drawtube can now be removed and I flipped the base plate over to reveal the 4 x bearings which cradle the drawtube in position.
Pic 5. It is this curved plate which must be shimmed one end to
minimise or totally eliminate the tilt.
Pic 6 shows the shim I made up sitting next to the curved plate. For my problem the shim had to sit just under the right hand end of the plate shown in Pic 6. I made the shim out of none other than a Guinness beercan
Pic 7 shows it all back together, the reassembly is just in reverse. I also removed all of my white and black texta markings on the drawtube which noted where each camera came to focus.
I fitted a small 34mm section of old tape measure blade, bent and flexed to match the drawtube curvature. Stuck on with 5 min Araldite. Makes a nice focus point index.
Steve