I have been looking at the WO rotolock focusser. Thanks for the pointer to the WO focusser drawings Stefan but I am concerned that it may not hold a QSI WSG 8 when pointing close to the zenith. Has anyone used one of these with a fair weight hanging off it (2 to 3 kg approx)
You can make the newest WO Rotolock rack and pinion focuser carry a lot of weight but it will require adjustment from new - they seem to set them too light at the factory. The construction and adjustment is very similar to other brands of R&P focusers including Takahashi. I'll resize some pics I have and show the adjustments here soon.
Firstly, if the drawtube has any sideways movement you can slightly tighten the two screws on top of the focuser; this applies pressure to the top Teflon pad bearing on the drawtube. You don't need to unscrew the screws, I removed one in the photo to see what was under it. The screws will only need to be tightened 1/16 or 1/8 of a turn.
Next you can try tightening the tension screw under the focuser to see if that gives you enough lifting power; it probably won't.
Move on to increasing the tension on the microfocuser bearing. Loosen the 3 grub screws on the black housing nearest the microfocuser. Then you need to loosen the grub screw holding the microfocuser assembly to the focuser shaft - it's accessed through the hole in the black housing near the 3 screws previously loosened. You'll need to rotate the focuser shaft to line up the hole with the screw.
Once you have the microfocuser out hold the silver knob while tightening the brass nut at the opposite end. To tighten the brass nut you'll need some multigrips or perhaps a circlip spanner. (previous versions had a knurled nut or flat sided nut and were easier to adjust)
If it's too tight to turn there may be threadlock that you could try loosening with acetone on a q-tip.
You can probably try 1/8th turn, reassemble and see how it feels.
When you reinstall the microfocuser assembly be sure that the grub screw meets with the flat side on the focuser shaft.
I have mine adjusted fairly tight to hold a decent load, the tradeoff being less smooth operation of the large focuser knob. The small knob/microfocuser is still smooth.
Here's a couple more pics showing the focuser internals. You can see the crosshatched area where the focuser lock pushes against, and the plastic part that the tension screw presses on.
Great stuff Tony. Those of us like me who are too chicken or just mechanically clutzy rely or guys like you to delve into the inner workings and let us know whats what.
I guess you're looking at the focuser for the SCT Ulrich, but it should be the same design as the 3.5" refractor focuser. The smaller diameter drawtubes are often easier to get working properly too.
These R&P models are the first of the WO focusers with decent enough design and enough adjustments to guarantee good operation. A lot of their previous focusers were woeful, especially the larger diameter drawtube models.
