Rack & Pinion Slop

Scorpius (Dave) · #1 10-12-2006, 05:05 PM

On the SW880 10" I just bought, it came fitted with rack and pinion focuser and like most budget R&P's there is an annoying slop when adjusting, which shifts the EP up a tad. I had the same problem with a cheap EBay 3" dob.

Having been spoilt with the 2" Crayford on my home brew 8" with a 10-1 reduction gear, I found that the following really does fix the problem. Wrap a single thickness of clear contact around the outside of the focuser tube just leaving a small gap either side of the rack. -- No more slop - worked well on the small scope and lasted very well. A light smear of petroleum gel finishes the job.
This idea has probably been suggested B4 but thought it worth a mention.

iceman (Mike) · #2 10-12-2006, 06:38 PM

Anything that fixes those old R&P's is a good idea

The crayford's are so cheap now I don't know why anyone would stay with an old R&P though

btw moving this thread to Equipment.

cjmarsh81 · #3 10-12-2006, 07:10 PM

Thats a really good idea. I have tried greasing it and continually tightening it, but it always comes back.

jase (Jason) · #4 10-12-2006, 07:38 PM

I bought my nephew a scope with a similar nasty R&P focuser. I used electrical tape with a light smear of petroleum jelly. Works a treat now.

Scorpius (Dave) · #5 11-12-2006, 12:52 AM

Quote:

Originally Posted by iceman

Anything that fixes those old R&P's is a good idea

The crayford's are so cheap now I don't know why anyone would stay with an old R&P though

Agree on that. I was going to take the 2" Crayford off the 8" but the mounting holes (70mm spacing) are closer than the SW880 (85mm hole spacing) and didn't want to drill holes in the new tin can. Probably knock up an adapter plate to accept the smaller base size unless someone makes one to directly fit the SW880.

Anyone know a source of the 85mm hole spaced 2" Crayford?

Scorpius (Dave) · #6 13-12-2006, 10:56 PM

Hi all: I bit the bullet and drilled 4 small holes in the new SW880 tube and made an adapter plate to fit my Crayford 2" 1-1/10-1 focuser which has 70mm hole spacing as opposed to the 85mm of the R&P. Operation went well and the 70mm spaced holes fitting just inside the hole in the tube. I also mounted my 9x50mm finderscope, which I modified the eye piece to take the Canon right angled viewer, which, has the advantage of a 2x feature and focusing ring.

I guess I will fit the R&P on the old 8" and offer that for sale in the new year sometime.

I reckon that also voids my warranty

ah well .....
Here"s a pickie of the two items.

Clear skies

iceman (Mike) · #7 14-12-2006, 06:02 AM

Much better! Nice job!