Making an 'O' ring

I'm making the o rings for the end caps for WTC's. The cylinder is 100mm and I'm using 3mm o ring material. I remember that the length of the ring should be 3xdia plus dia of o ring. Is the main dia the dia of the end cap, or the dia of the base of the o ring channel. many thanks Roger

I must admit to a bit of trial and error when using O ring cord like this, or I copy the length of a previous one.

You make the length so that the O ring beds down well in the groove without being too stretched or being so loose that it gets dragged out of the groove when you push things closed.

Using cyano to glue the cut ends (I find cut at 90 deg now rather than at 45 deg) is so quick and easy that you can easily shorten the length anyway.

Why would you want to make an 'O' ring with the inherent chance of it failing and leaking at the joint when you can buy proper 'O' rings for a few pence each???


Mark.

Roger, inner dia,of o ring grove.

many thanks.

Hi Mark,

Often need large diameter O rings e.g 100mm and they are often not standard sizes. Certainly wouldn't make little ones.

Hi Mark,

I should explain that I never use acrylic tube anyway. PVC sewer pipe for me. It is tough and cheap and I have never seen a huge virtue in transparency! (If you have to keep checking for a leak then it needs to be built better.)

In Cumbria the woods are not exactly full of local motor factors and I use mail order a lot. To complete my "backwoodsman" approach I just find O ring cord very handy once you have a stock.

But thanks for the tip. I will check on the O ring stockists.

We all have lots of different ways of solving problems but none of them are compulsory!

Lots of smileys (I can't find the smileys panel on here!) and I look forward to seeing you again soon, in Surrey!

David

Hi Mark,
The last tube I built used standard kitchen waste pipe,(41mm) and I machined the end caps from perspex and was able to use an 'o' ring that would fit arround a sink plug.

My next tube was to be 100mm OD and I decided to treat myself to a piece of acrylic tube. I again machined my first end cap from perspex ending up with a dia at the bottom of the 'o'ring slot of 3.523 inches dia as I am using 3mm 'O' ring. Sorry about the use of both metric and imperial, but my lathe, vernier gauge and micrometer are all in inches. So reading your comments about possible cracks to the tube when using 'joined' rings, I would be most grateful if you could obtain for me a 3mm section ring with an inside dia of 3.523 inches. many thanks for your help

Roger.

Mark, that would be great. Can I have a few more days to machine the inner cap, which uses 80mm tube and ask you to send both sizes together.

blessings

Roger

Hi Mark,
'Long, Long, time ago'..... as the song goes, you said you would be able to get some 'o' rings for me. Is the offer still open?

Roger

I have just been refitting my R class with my newly made piston tank and I tested it at the Barrow pond yesterday (FFffffreezing and I nearly lost the sub in the middle after knocking the rudders off!!!! The piston tank and the rest of the sub worked well though.)

The reason for this post is that I also replaced the home made O ring with a proper commercial one. What a difference! Much easier to push the end cap in.(So easy that the unsecured end cap could be pushed out by the internal pressure from the piston tank - watch that one!)

So I really DON'T recommend using O ring cord any more.

David