[Cartel, LLC]

I am needing to cut an inside square o-ring. I haven't really researched it yet as far as tooling or how to program it. I'm just curious if anyone else has done this and if so what type of tooling did you use? Thanks!

[cadman@teluspla]

On a lathe or mill?

[Cartel, LLC]

Sorry. I guess that's important. It's on a mill. I'm machining a bore for a brake caliper and going to put an o ring inside the bore instead of in the piston. I've thought about just using a keyway cutter? I don't know if it's as simple as that or ???

[Geof]

You could cut a useable O-ring groove with a Woodruff cutter and chamfer the top edges using a threading cutter, but I am not sure your design having the O-ring in the bore is a good idea.

Make yourself a drawing of your design and also a drawing of a conventional design with the O-ring in the piston. Then figure out the forces acting on the O-ring from both the fluid pressure and the direction of movement of the piston in the bore.

With the conventional design the fluid pressure pushes the O-ring forward but as the piston moves the O-ring is dragged backwards in contact with the bore.

With your design the fluid pushes the O-ring forward and the motion of the piston also drags the O-ring forward. I know the piston does not move much but this type of arrangement may be more prone to failure due to the O-ring extruding into the clearance between the bore and piston.

[RCaffin]

I am needing to cut an inside square o-ring. I haven't really researched it yet as far as tooling or how to program it. I'm just curious if anyone else has done this and if so what type of tooling did you use? Thanks!

For a milling cutter:
Take a bit of round silver steel rod and some 1/8" tool steel. Machine a slot in the end of the silver steel and braze the tool steel in place. Grind tool steel into required shape. Btw: round off the inner corners for stress relief.

Poke cutter down centre of hole, move slowly to side, g2/3 around as needed.

I make a lot of custom tooling like this, and it works fine. later on you get into using a diamond wheel for the shaping, but a simple disk-shaped point is enough.

Cheers
PS: but it IS better to put the O-ring on the piston, as OP said.

[cadman@teluspla]

I don't know if you are aware of it but I will throw this out there.
The geometry for an o-ring groove is not as straight forward as it may seem.
The side walls should taper between 2 to 5 degrees.(4 to 10 included angle)
The radius at the bottom of the groove varies between 0.005" - 0.035"
depending on the size of the o-ring.(0.005 - 0.015 for a 1/16" cross section
0.020 - 0.035 for a 1/4" cross section) Several in between.
Over 1500 PSI you should consider allowing for back-up rings.
Just thought I would share this info.

[tfro]

I don't know if you are aware of it but I will throw this out there.
The geometry for an o-ring groove is not as straight forward as it may seem.
The side walls should taper between 2 to 5 degrees.(4 to 10 included angle)
The radius at the bottom of the groove varies between 0.005" - 0.035"
depending on the size of the o-ring.(0.005 - 0.015 for a 1/16" cross section
0.020 - 0.035 for a 1/4" cross section) Several in between.
Over 1500 PSI you should consider allowing for back-up rings.
Just thought I would share this info.

Most standard o-ring grooves can have walls up to 5 degrees, but 0 is extremely common (I'd say the norm). Using a back-up is dependent on the elastomer and the application. Many elastomers will hold 10,000+ psi at elevated temperatures with no back-up in place. Back-ups will actually lead to sealing issues at low temperatures/low pressure applications for some elastomers.

Here's the go to resource for o-rings if you don't have an existing standard to use: http://www.parker.com/literature/ORD...g_Handbook.pdf

Also, in dynamic applications I've never had an issue with an internal/external glands, use what makes sense for installation and protection of the critical sealing surfaces. Dual acting hydraulic cylinders have both styles and work just fine...