O-ring design choices

J

JohnAspinall

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I'm making a vacuum chuck adapter for my woodworking lathe. I need to get a seal as my adapter fits inside a 10mm bore.

I've searched most of the threads here that mention O-rings, and tried out several of the on-line O-ring calculators that were mentioned in those threads. If I stick to standard sizes (ISO 3601, or AS586), I end up with a design that either (1) stretches a 011 to its limits, or (2) has a very loose fit with an 012.

Any suggestions? All info and comments appreciated.

( Here are the nitty gritty details, if you want to try your hand at the design. Bore is 10mm nominal. I don't have a set of pin gauges, but using drill bits as feelers, I get a loose fit with an X drill at 0.393, and a no-go with a Y drill at 0.401. Those are the actual measured sizes; I know the nominal hole they drill is 3-4 thou larger.
The adaptor carries the O-ring grooves on its outside; it is the male part of the junction.
This is for vacuum, so pressures are low, and this is a static fit.)
 
Baring the ability to make your own O ring, make your parts to fit / utilize existing O rings. Or you could just stretch an 11 to it's limits & see how long it lasts. Chances are the stretched O ring will adapt & give a satisfactory lifespan.
 
You probably know this but an o ring groove is square bottom not radiused.
 
"You probably know this but an o ring groove is square bottom not radiused."

"And an O ring slot has a 5 degree taper on the sides. "
_______________________________________________________________________________

I didn't know this. I've never had to do O-rings---yet.

I'm smarter than I was a few seconds ago- I know how to cut the tool now- thanks!
 
kd4gij said:
You probably know this but an o ring groove is square bottom not radiused.
Click to expand...
The depth of the cut of the o-ring groove is also to a fairly tight tolerance, and is not perhaps what you might guess. There are also differences in the grooves for static and for sliding o-rings. O-rings live a tough life, but do an amazing job of working and lasting much longer than might be expected from what they have to put up with, without leaking. There are also lots of materials o-rings are made of for special purposes beyond the "standard" black buna-n rubber.
 
I did not know about the o-ring channel bring square cut but I will definitely be looking into the design of future projects needing "Glands" (thats the technical name for the o-ring channel/seat which I also just learned:sherlock::grin:)

kd4gij.....Thanks for sharing that info. Before i read your post I ALWAYS thought/assumed that the groove the o-ring sat in was semicircular and would have never figured square cut and are much more complicated than I ever imagined.
 
The Parker o-ring handbook (which you can download from their website) has lots of good information on o-ring gland design and dimensions for various pressures and sealing scenarios. Start there and adjust the diameters if necessary. There are also lots of odd size o-rings besides the standard 2-xxx sizes, all listed in the handbook appendices.
 
"There are also lots of materials o-rings are made of for special purposes beyond the "standard" black buna-n rubber. "
That's a fact, back in 1994, I believe, right a,round the time we stopped using R12 freon.
The auto industry switched over to a blue or green colored o-ring to seal the ac hoses and tubes (high side-suction side).
Cars and trucks ac systems leaked at every o-ring joint until this change was made.
I didn't know there was a 5 degree angle.
 
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