Correct hole size for a given O-ring
Correct hole size for a given O-ring
(OP)
The O-ring is AS568a -008.
This is a nominal size 3/16" ID x 5/16 OD" x 1/16" wide.
For a shaft .311" I decided on a gland grove of .0625" depth x .070" wide.
Tolerance on the shaft is +.000 / -.002.
The shaft is mild steel. And the application is a compression screw running in 6061 aluminum head on a model diesel engine.
What is the correct size for the bore?
I guessing +.001"
Meaning that if the shaft is in fact .311" then the bore would be .312"
Or, shaft .310" and bore .311"
Am I correct or not?
Should I be tighter than .001? Or less?
This is a nominal size 3/16" ID x 5/16 OD" x 1/16" wide.
For a shaft .311" I decided on a gland grove of .0625" depth x .070" wide.
Tolerance on the shaft is +.000 / -.002.
The shaft is mild steel. And the application is a compression screw running in 6061 aluminum head on a model diesel engine.
What is the correct size for the bore?
I guessing +.001"
Meaning that if the shaft is in fact .311" then the bore would be .312"
Or, shaft .310" and bore .311"
Am I correct or not?
Should I be tighter than .001? Or less?





RE: Correct hole size for a given O-ring
--Scott
http://wertel.eng.pro
RE: Correct hole size for a given O-ring
I suggest you download a copy of the parker o-ring handbook
h
The optimal dimensions depend on whether it is a dynamic or static seal and whether the shaft spins or is stationary etc. See page V-25 for the various dynamic seals or section IV for static seals. I have carried a copy of this handbook for 35 years (first published 1957). I consider it the bible for o-ring applications. If you are really lucky, the local Parker dealer can get you a hard copy.
Timelord
RE: Correct hole size for a given O-ring
In the UK I seem to recal a British Standard that had this information for standard sizes, not sure I've seen the same in the US.
KENAT, probably the least qualified checker you'll ever meet...
RE: Correct hole size for a given O-ring
I studied the Parker catalog but while it helped me decide on the proper grove for the ID I could not find anything to tell me the correct size for the bore.
This is a static seal, but it does have limited rotation if the compression screw is adjusted to raise or lower the compression slightly.
Anyway, thanks to everyone for the replies.
RE: Correct hole size for a given O-ring
Page IV-5 of 20 shows the gland you want. The dimensions are tabulated on the following several pages for each size o-ring including the bore size (columns A or D). A Parker 2-008 is the nominal size you gave. Another thing, you may have trouble streching this small of an ID over the OD of the rod.
Timelord
RE: Correct hole size for a given O-ring
Static Radial Seal (for -008 O-ring)
Bore Dia = .295" +.002/-0
Piston (Shaft) Dia = .294" +0/-.001
Piston Groove Dia = .186" +0/-.001
Gland Width = .105" +.010/-0
Pressure limited to 1500 psi.
Obviously the above only applies for suitable surface finishes.
RE: Correct hole size for a given O-ring
I see it now.
Thanks.
RE: Correct hole size for a given O-ring
The gland dimensions determine the correct squeeze for the o-ring and allowance for the o-ring to displace when squeezed in the gland without rolling. I believe the actual cross-section of the 1/16 o-ring is .070 inches.
The Parker handbook describes the pressure/material/extrusion relationship as well as other seal and gland data. The Parker handbook was my friend for years, too.
Ted
RE: Correct hole size for a given O-ring
Note that the ether used in model diesel engine fuels is very aggressive with any standard O ring material (eg Viton, nbr, etc, etc.)
Hence the reason contra pistons are usually a transition fit.
Cheers
Harry
RE: Correct hole size for a given O-ring
"Note that the ether used in model diesel engine fuels is very aggressive with any standard O ring material (eg Viton, nbr, etc, etc.)"
This is not a contra piston. It uses a compression plug and Viton o-ring and I don't know how ether affects it.
But it's worth looking into.
Thanks.
RE: Correct hole size for a given O-ring
For a male gland of seal diameter A, gland diameter of B1 and elastomer cross section CS then the percentage squeeze is:
%squeeze=[1-(A-B1)/(2 CS)) X 100.
Likewise, the percentage stretch is:
%stretch=[(B1-d)/d] X 100, d=inner diameter of o-ring.
The female gland uses exactly the same equations, except the seal diameter is now B and gland diameter A1.
%squeeze=[1-(A1-B)/(2 CS)) X 100
%stretch=[(B-d)/d] X 100, d=inner diameter of o-ring.
Typically the percentage stretch regardless of o-ring size or application, static/dynamic, is 2% to 3%. However, the percentage squeeze varies according to static application and cross sectional diameter, or dynamic application and cross sectional diameter. I follow the Parker-Hannifin suggested squeezes to the letter in this regard.
A lot of engineers will simply interpolate between line entries of their o-ring size and application. This is alright, but I've found that in the case of bastardized gland geometries or cross sectional diameters of o-rings made from primer cord of differing thicknesses, that the pure mathematical approach is much simpler.
Analytically, the equations regarding squeeze can be mathematically determined noting the o-ring shape deforms from a circle to an ellipse. This deformation is responsible for "gland fill", which is why the gland width needs to be larger than the cross sectional diameter of the o-ring. You can determine this width by usage of Poisson's Ratio, noting the mechanical deformation of the rubber.
But I do agree with the previous entry, just use the Parker-Hannifin Handbook. It is absolutely the best source on the market and should be sitting right beside the Machinist Handbook on your book shelf.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: Correct hole size for a given O-ring
I have downloaded the Parker handbook and think I've got it figured out.
The bore size should be .312 with a gland depth of .050.
RE: Correct hole size for a given O-ring
The other link only provided me with the first 3 pages ;)
RE: Correct hole size for a given O-ring
It's the way Adobe organizes the virtual book these days! The whole book is there.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada