celestron ed100 upgrading focusser

[A McEwan]

Hmm... very handy!

[kniclander]

"I loosened the two very small recessed allen bolts in the top of the focuser body. These apply pressure to a strip of teflon (or similar) which sits atop the drawtube, inside the body, and helps to even out the travel of the drawtube. I loosened the bolts until they were completely loose but not removed. They are TINY. They get lost easily."

apparently the previous owner of my scope did indeed lose one of the grub screws. presumably (excuse the stupid question) if a 2mm allen key fits it then it's a 2mm grub screw? And are the threads standard or would I need to ascertain/ specify a thread size?

[spaceboy]

Yes 2mm key = 2mm grub. While you make adjustments put a collimator in so that this remains true after adjustment. Refractor Collimation

[kniclander]

well, the deed is done. stripped, re-greased, teflon strips added and teeny grub screws adjusted. There is definitely far less slop in the focusser (ie side to side/ up down wobble) although it's not quite as smooth as I'd hoped and also there is a little slack in it, ie when you turn the focuser wheel, it turns about 2mm before it engages with the drawtube and the drawtube actually moves. Is there anything that can be done to improve that?

thanks everyone for all your help, especially Spaceboy and Ant:icon_salut:

[A McEwan]

Sometimes the trade-off for the better lubrication is that the pinion takeup becomes a bit more noticeable, as it has in your case. I'd suggest trying a different type of grease and definately increasing the shims to remove that slack completely.

It is simply a matter of repeating until you're happy with it really. Experiment with different tension settings from the grubb screws too - they can have a significent effect.

Congrats on taking the plunge though - it can be a bit daunting the first time. Think of all the money you saved!

Ant

[kniclander]

oh god, just done it again - as if collimation OCD wasnt bad enough...

[spaceboy]

R&P inherently have backlash and I'm sorry but other than taking the rack & pinion to a local engineering company and saying improve on this there is not much else you can do. As I mentioned before the most important thing is keeping your collimation spot on to ensure your getting the best from your scope. Shimming and adjusting the draw tube will do this but you will most likely find that at the same time this improves the movement. Improve being the preferred description as don't get me wrong it will never be as good as a crayford but neither will it be as expensive as a crayford. I admit I would like a DS focuser on the C100ED but I could live with out a crayford as some cheaper crayfords are not without there own degree of slop. To deal with any backlash I do get in the R&P I go either side of focus to see where the sweet spot is then come to focus slowly from the one side of focus. (if that makes any sense) After doing it a few times it soon becomes second nature.