which O ring

I need a bunch of little O rings for my Mazak lathe...

There's two O rings on each plunger, six plungers on the turret. Everything else is metric on this machine so I assume these are also. The ring slots in the plunger measure 6.95 mm ID 9.96 mm OD and 2.6mm wide. The bore the plungers slide in look to be an even 10mm.The O ring itself measures 1.75mm cross section after drying it out.

McMasterCarr has a: 1.5mm wide by 7 ID, 1.6mm wide by 7.1 ID, and a 2mm wide by 7 ID.

In English units, I've got steel at 0.273ID, 0.394OD, .100 wide. O ring measures 0.069. Awful close to 0.0625 or 1/16" and McMaster says 1/16 measures 0.070 actual.

McMasterCarr has a 1/4"ID by" 3/8 OD in English.

Which O ring should I get?


Reply to
Karl Townsend
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The 2x7 sounds about right. It will install in the bore with about 10% compression which is close to the recommended range, IIRC.


Reply to
R. O'Brian

That is a size 010 o-ring. The actual dimensions of the o-ring are- ID-.239 CS-.070 If you install a .239 ID o-ring on a .273 OD shaft you will be stretching the o-ring approximately 14%. Stretching the o-ring 14% will reduce the cross section by approximately

8%. This will reduce the Cross section from .070 to .0644. The gland is (.394-.273)/2= .0605 Your % squeeze will be [(.0644-.0605)/.0644 ]x 100= 6%. That's not very much. I would shoot for a minimum of 15%, especially with a .070 cs o-ring. The o-ring CS tolerance alone is +/- .003, and small CS o-ring are famous for immediate set of very low % compression. Will it work?- Most likely. Will it weep oil?- Most likely, depending on the concentricity of the gland to the OD especially if deflected to one side.
Reply to

1.5mm x 7mm. Equates to 7mm ID x 10mm OD, that's what your groove relates to. If you use any other size you will either cut them on assembly or experience premature failure.


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