make thrust bearings without grinding? CNC lathe?

[pmurdock]

ok.. so I want to make a few bearings.. these are thrust bearings.

See wikipedia for photo of what I'm talking about

http://en.wikipedia.org/wiki/File:Th..._din711_ex.png


all the faces of the bearing require 32 Ra finish.. no prob on the a CNC lathe.

What I do have a question about is the raceway. I would like to get a raceway with a finish of 8 Ra or better. I'm wondering what the general consensus is on achieving that?

I will start with 8620 steel machine everything to size (except the raceway - which I imagine I should oversize? how much is needed) then send it to the heat treaters for case hardening (carburizing - case depth - any recommendations?) and then mount it back in the lathe and hard turn the raceway.

Now I have been looking at some Kennametal inserts (wiper technology). See Kennametal catalog here (http://www.kennametal.com/images/pdf...OSFEVMCQFB0IV0) see page A20-A23

These inserts claim a potential Ra of 1 which I find hard to believe, but makes me think that 8 Ra just might be possible. Anybody have any experience machining to these type of surface finishes? I'd like to do them in house if possible and can't justify buying a grinder just yet.

How about a round insert like an RCMT - perhaps those might do the trick - though I don't see any PCBN or DIAMOND versions of the RCMT.

Perhaps machine to size or + 0.0002 or so and then only worry about polishing the raceway after case hardening (read that in a post by HuFlungDung).

cheers!
Paul

[RICHARD ZASTROW]

I've seen your method done. It was on the turntable for a fire engine ladder truck. The groove was turned in both plates on a Vertical Turret Lathe. They are then burnished by rotating the table with the rolling balls sandwiched between the plates.

The grooves are then flame hardened. Any distortion is neutrallized by the weight of the ladder rig and the clamping of the plates.

This is probably not done this way anymore. Slewing rings are now more available commercially.

Dick Z