Drawtube wiggle

[david_taurus83]

Had odd shaped stars the other night and upon investigation I noticed there is quite a lot of play in the drawtube. Its hard to catch on video as your peripheral vision can see more but there's a definite wobble. If the rack is at the top then up and down is OK. It wobbles side to side. I've took it off the OTA and there is definitely teflon strips on the OTA side but I can't see any on the camera side. Any ideas? I've never had an issue with these 2.5" R&P focusers until now.

[dobblob]

It's been a while ago and I made no photos of the operation but I can at least attempt a verbal description.......

My R and P focuser had a similar slop. The tolerances were just too forgiving. As I racked in and out I could see out of focus stars , then in focus stars, then out of focus shift across the FOV.

This was a problem as I was replacing the EP with a camera at different focus points. Very annoying having found and centered the guide star in the EP and find it shifting at a different camera focus point.

Very crudely I made up some two part epoxy weld and packed the inside of the focus assembly to provide a long collar around the focus tube and of course avoiding the rack and pinion parts.

I greased the tube first to ensure it would slide in the epoxy collar and not adhere to it. When hardened I had perfect surface contact and no slop over a couple of inches of travel.

I have to admit that I was probably lucky that the focus tube was set parallel to the optical axis. I was careful to let it cure with the draw tube at the central point of travel.

[david_taurus83]

I've sorted it now, I think! There are 3 teflon strips that help align the tube and there are 2 layers of teflon in each strip. The camera side of the outer tube is a little larger than the scope side so that's where there appeared to be the most play. I separated the teflon layers and put a small piece of insulation tape between the layers. This has made it a much more snug fit but it still racks in and out easily via the focuser. It feels much more like the focusers I've had on previous scopes now.