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Old 01-19-2009, 11:01 PM #1
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everything you need to know about ORINGS!

ok, so in the last few days I've had a few people asking for parts made that have oring glands (grooves) in them, and I'm tired of having to try and explain why a 1/16" cross section diameter oring needs a shallower gland than 1/16 to sit in. SO the point of this thread is for good reference when your going to make apart that requires oring grooves. the following pages give all the info the hobbiest needs for making PROPER sized oring glands, oring material selection, and PROPER oring diameter clearances.





in addition the specification for a good majority of the AS568 orings can be found here

On top of that ZDS has a very good sorce of information that can be found here

OR ,what most of you want to see, the hard numbers for the size gland you need for a specific oring size look here
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Old 01-19-2009, 11:02 PM #2
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Here is a Matlab code to approximate oring friction force. you should be abel to copy and paste it right into matlab.



% Cliff Burger
% oring friction force calculator

%to calculate Elastic Modulus. USE HARDNESS SHORE A VALUES!!
T=200; %Oring Tensile stength (psi)
E=350; %Oring percent elongation
Y=T/(.001*E);

%if elastic modulus is know, uncomment "Y=" section and comment previous
%section. % Resorce: http://www.matbase.com/material/poly...ber/properties
%Y= ; %(psi)

D3=.25; %Bore Diameter (in)
D4=.125; %oring gland diamter (in)
d=.07; %ACTUAL measured oring cross sectional diamter (in)
r=d/2;
Ff=(2*pi*D3*r*Y)*(1-((D3-D4)/(4*r)))*(1-((D3-D4)^2)/(16*r^2))^.5 %Friction force (lb)



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Old 01-19-2009, 11:13 PM #3
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Old 01-19-2009, 11:23 PM #4
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this thread = win. should be stickied for people that need the information and dont know where else to find it....

btw, zoom window feature on new mouse FTW
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Old 01-19-2009, 11:27 PM #5
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heres another good source http://www.parker.com/literature/ORD...g_Handbook.pdf
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Old 04-15-2009, 01:37 PM #6
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just added another link...why isn't this sticked yet??
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Old 04-19-2009, 07:52 PM #7
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Disagree about the gland depth!!!! Go looser, be happier!
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Old 04-23-2009, 10:53 PM #8
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lol. those are the specs i've used so far on all my orings, and i haven't had a single sealing issue yet. they have worked good for me so i'll stick with them.
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Old 04-23-2009, 10:56 PM #9
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good info cs900
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Old 04-23-2009, 11:35 PM #10
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If by work you mean they'll seal pressure, then yes! But the grooves will end up waaaaaay tighter than they need to be for a moving part. The rings will wear out quicker and need lubrication more. Also technically more friction although that's not often an issue, depending on the forces being used.

When I design a moving o-ring groove (for paintball...nothing else), I usually match the outside surface to the theoretical OD of the o-ring, then stretch the inside surface about about 0.002-0.003 larger (on the radius, so twice for the diameter). Though it depends on the size of the o-ring since larger ones will stretch different than smaller ones. It amounts to quite a different diameter than you get from suggested numbers that come from industrial applications guides like the one in the first post.

But in the end, experimentation is REQUIRED, no matter the situation. The best way to do it is to machine several parts to use for testing and use the best one to draw the final dimensions.
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Old 04-23-2009, 11:47 PM #11
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agreed.

however the orings themselves will vary more than those tolerances you stated above, so it really is a crap shoot working with orings. that's why we have standards to follow
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Old 04-24-2009, 12:00 AM #12
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You know, I've heard that before, but I've come to think it not true as of late. The published tolerances on the buna rings I personally use is +0.0025, but I swear to Gort it has to be tighter limits than that. It just seems like fits are too consistent from one ring to the next...even different batches over months' time. Of course that's not scientific in the least, I don't want to sound like that
I'm not sure what the specs are for supposedly "higher-quality" materials like urethane or hydrogenized rings, makes my head boggle thinking about it (lol) hell it could be the same for all I know...
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Old 06-04-2010, 02:28 PM #13
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sorry to bring this back from the dead guys, but i've recently been doing a failry particular design for a customer, to the point where I need to approximate the friction due to the oring squeeze. So I made a cool little matlab code to calculate it, and I figured maybe someone here might use it some day. Everything is pretty clearly labeledso you know what variables to input into the equations. Any questions, or if you want to mock me for my poor coding skillz, please feel free to post up.

the code is posted in the secoind post above....
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Old 06-04-2010, 02:35 PM #14
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Awesome, I love matlab.
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Old 06-04-2010, 03:00 PM #15
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yeah, there are a dozen better ways to code that, but i wanted something quick and dirty I could just get to the design, lol. feel free to put some prompts in for the variables...I almost did that, but then realized I was too lazy....
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Old 06-04-2010, 06:14 PM #16
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this for me?
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Old 06-04-2010, 07:09 PM #17
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yup
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