Mods to pressure plate on Altair Astro focuser

[fwm891]

Like others I've had a few problems with hanging a filter-wheel and a cooled CCD camera from my bog standard focuser. As we've had nice weather I decided to try and do something about it

The scope is an Altair Astro 8-inch f4 newtonian with supplied focuser.

I've replaced the original tension/pressure plate with a new one that contains set a pair of small ball races (7 x 3 x 3 mm). See photos of roller assembly. A screw behind the roller assembly supplies the needed pressure.

The focuser had a neat hole taking the locking screw which simply applied a point pressure to 'lock' the focuser moveable tube. I reasoned that if I removed the point pressure and replaced it with a pair of ball races, I should be able to get the required pressure to stop the focuser tube sagging when loaded and still be able to adjust for focus

On the opposite side of the focuser tube are four ball races which act as fixed guides.

By applying pressure to the new ball races I simply 'push' the focuser tube into the guide bearings on the opposite wall.

I re-drilled and taped for the locking screw but found that by applying a little extra pressure with the original tension screw the whole assembly locked anyway.

I have a small lathe with a vertical slide which enabled me to do the small amount of milling involved with this mod. Had I modified the original pressure plate then the mod could be done with a drill and file to square out the through hole.

It all works well with regards to supporting a load - I now need to look at the machined flat that the roller presses against as that shows very uneven wear...

[fwm891]

Update:

I've attached a schematic to (hopefully) show the position of the pressure rollers with reference to the guide rollers.

I've also been playing with the tension and can now use both coarse and fine focus knobs with the tension set to much higher limits than previously. It would lock-out the fine focus knob before making small adjustments almost impossible.

There doesn't appear to be any sag from the central focuser tube with the Atik 383L+, SX Usb filter wheel, TS OAG, Baader MPCC and a short 35mm extn tube hanging out

I'm hoping tonight to finally get a chance to try the mod out in anger....