Need Help!- Spherical Radius - Improving suface finish

[mkslice]

Hello, I'm new here and hoping someone can help.
I have a pin (3/32 dia.) that requires a spreical radius on one end. The radius is .0625, so it is small and the depth is only .005" We need to improve the surface finish from a Ra 32 to Ra 2 or 4. Material is 440C hardened to Rc 55-58.
Any suggestions on processes to rework parts to achieve the finer surface finish? We have tried lapping, but is very time consuming considering we have thousands to do.

Thanks in advance for any help with this.
Marc

[easymike29]

If your pin is long enough you could consider a centerless grinding attachment on a surface grinder. A DedTru for example.
http://www.unisonemail.com/PDF/Broch...dtrusystem.pdf

[mkslice]

Thanks easymike for the reply.
I overlooked describing that the radius is a concave surface. I don't see how that grinding attachment could create that surface.
The pins are 1.5" in length, so lots to hold on to.

Marc

[easymike29]

You dress a convex radius on the grinding wheel and grind a concave radius in the pin while it's rotating.

[harryn]

How about electro polishing.

[HuFlungDung]

Some of the optical machinists have a trick for machining perfect spheres on the mill: they use a flycutter with a known swing diameter, above the workpiece sitting face up on a rotary table. The flycutter is tilted off axis so that it engages the whole surface to be machined, and the flycutter spins whilst the rotary table makes one full revolution and the surface is done.

The axiomatic principle is that a cylinder can sit on a spherical surface and make line contact all round its perifery.

So even though your workpiece is tiny, some sort of grinding rig could be devised to create a concave surface. A lathe spindle is not required since the part is only making one revolution and it need not be fast turning. But you will need a high quality high speed grinder to run a tiny diameter stone, with smaller diameter than the diameter to be polished. I'm thinking maybe some sort of dental drill.