O ring size for 50mm Finder?

[Orion]

Hi,

I need an "O" ring for an Orion (US) 50mm finderscope, you know the one that allows the finder to sit in the finder mounting tube. I don't have an old one to guesstimate the size from, I can of course measure what I think might be right, but I just wondered if anyone knew or had any suggestions where I could obtain one.

cheers

[steppenwolf]

It is 48mm dia. assuming that it is a re-badged Skywatcher (Synta) unit which I believe it to be.

[Orion]

It is 48mm dia. assuming that it is a re-badged Skywatcher (Synta) unit which I believe it to be.

steppenwolf,

Would that be 48mm inner diameter?, do you know what thickness/dia the O ring itself is.

thanks

[steppenwolf]

Unfortunately, I don't know that - I know that the bag my replacement came in was labelled 48mm! I can't offer to take mine off as they go brittle in use and I suspect it will break like the original. I guess that measuring the groove that the ring sits in by using a digital calliper would be a good start as this would give an indication of the internal diameter but remember that the ring is an interference fit so I would allow a reduction in diameter of, say, a millimetre. It is not that critical because I used an elastic band on mine for some time after the original O ring broke and it stayed correctly collimated with the telescope!

[Orion]

Unfortunately, I don't know that - I know that the bag my replacement came in was labelled 48mm! I can't offer to take mine off as they go brittle in use and I suspect it will break like the original. I guess that measuring the groove that the ring sits in by using a digital calliper would be a good start as this would give an indication of the internal diameter but remember that the ring is an interference fit so I would allow a reduction in diameter of, say, a millimetre. It is not that critical because I used an elastic band on mine for some time after the original O ring broke and it stayed correctly collimated with the telescope!

Measured the sizes with a dig' vernier, so thats no problem, its just knowing how much stretch to allow/change for size, and then finding someone who sells them in very small quantitys.

I've sent a weeping email to Orion (US) Tech support, if they dont come through it looks like it might be an elastic band solution.

You would think all the major telescope suppliers would have some sort of replacement parts system in place for all their bespoke odds & ends, like O rings, thumbscrews, lens caps etc.

Dave

[Tinners]

Like this company?

British Standard Size O-rings Seals NBR Rubber BS102-BS178 from Polymax

[glowjet]

Thats an extremely useful contact, thanks Tinners.

John.

[Tinners]

Although I think it has a £10 min order..

..maybe a good time to replace all the leaking seals in your radiator valves.

[Orion]

I think my problem may be solved by a very kind forum user.