Clicky collimation screws after a few months of disuse

[sockatume]

I dusted off my Skywatcher Heritage 130p (who knew that lockdown would coincide with such bad weather?) and decided to check the collimation as I'd not done that in about a year. The collimation needed a little bit of a tweak, and was surprised to find that all three of the actual collimation thumbscrews (not the locking screws!) now click quite distinctly and noisily in to the exact position I had it in previously. It's like it has a detent now! I'm not sure quite how that could be happening mechanically but it seems that something must've worn or seized. Should I be worried about that? The screws otherwise turn smoothly and it isn't (yet) getting in the way of adjusting the collimation, but if it picks up a click for every position it's left in it soon will!

[DaveL59]

overtightened locking screws perhaps, deforming the threads slightly? or a touch of corrosion which can be cleaned up if you've a tap and die of the correct size.

[sockatume]

I had the locking screws just finger-tight but maybe the metal is a bit soft. There's probably some spares kicking around online I guess?

Edit - I'm being silly, if it becomes a problem I could just equally loosen all of the knobs and get far enough away from the clicky spots while having the same collimation..

Edited July 18, 2020 by sockatume

[NGC 1502]

One possible way to sort this is to remove the mirror and cell from the tube, strip out the collimation screws and clean up the threads as already suggested.  This includes the screws themselves the threads they pass through plus any nuts etc. Reassemble with a small amount of grease on the threads. Not much grease is required but best if it’s right along the length of the thread. You can achieve that by running the threads along their full length a couple of times after applying the grease.

Of course it’s vital to protect the mirror surface from damage or grease contamination.  Mirror cells are basically very simply constructed so if you go carefully you’ll be fine.  Perhaps place a piece of tape on the cell and a corresponding piece on the tube, avoiding any difference in spacing of bolt holes in a different orientation than the original position.

Ed.

[sockatume]

Thanks both (and please excuse the late reply!). I'll put cleaning up the threads on the to-do list for any future serious maintenance of the 'scope (e.g. if I ever need to wash the mirror).