Attaching threaded 'scope rings to threaded plate

[DarkKnight (Kev)]

I want to attach a pair of guide 'scope rings to a Losmandy dovetail plate. Both have 1/4" threaded holes, hopefully with the same pitch.

I seem to recall reading or hearing somewhere that it is not a good practice to screw two threaded items together as they may not mate perfectly and I can sort of understand why.

If this is a problem I think I can see two possible solutions. Firstly, use my small round file to remove one lot of threads, probably from the 'scope rings, or I was wondering if an appropriate spring washer would take up the slack in the mounting face.

Any advice appreciated.

Cheers

Kev

[gary]

Hi Kev,

What you are referring to is known as a "clearance hole".

The O.D. of a 1/4" thread is 1/4".

If you have a drill press, you could drill out the scope ring threaded mounting holes.

Ideally drill them with a 6.2mm drill bit and then use a 1/4" reamer
to ream them out to exactly 1/4".

But a round file and patience will get you there. Has been known to
work for the occasional escaped prisoner.

[Kunama]

Originally Posted by DarkKnight

I want to attach a pair of guide 'scope rings to a Losmandy dovetail plate. Both have 1/4" threaded holes, hopefully with the same pitch.

I seem to recall reading or hearing somewhere that it is not a good practice to screw two threaded items together as they may not mate perfectly and I can sort of understand why.

If this is a problem I think I can see two possible solutions. Firstly, use my small round file to remove one lot of threads, probably from the 'scope rings, or I was wondering if an appropriate spring washer would take up the slack in the mounting face.

Any advice appreciated.

Cheers

Kev

Yes, it can be done but in order to align the ring at 90º to the plate there is likely to be a gap. Measure this gap with a feeler gauge and use a washer slightly thicker than the gap. This saves altering either the ring or the plate.

Otherwise I would be inclined to drill the hole in the cheaper part to let your bolt pass unhindered by the existing thread.

[DarkKnight (Kev)]

I think I can work around the problem by using the recessed non-threaded slots on the Losmandy VUP4 plate.

This will only give me 2.75" between the new rings as opposed to 3.25" on the dinky mount that came with the 'scope, however as the new rings are much more solid I don't foresee a problem. But then I've had the odd 'whoopsie' to date in my not so short and often frustrating journey into things 'Astro'.

Cheers