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Mike Burdick
02-18-2005, 04:40 PM
I was wondering how Concentric makes their live center to compensate for work piece expansion. Are the bearings free to move axially and the thrust pressure (from spring or whatever) is what keeps the bearing from rotating in the seat?

Thanks...

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[This message has been edited by Mike Burdick (edited 02-18-2005).]

Lynn Standish
02-18-2005, 05:36 PM
The MSC catalog has a cutaway view that explains it better than I could. Try here:

http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=1537

Mike Burdick
02-18-2005, 07:08 PM
Lynn,

Thanks for taking the time to find and post the link!

Tom CPM10V
02-18-2005, 11:16 PM
Currently rebuilding my early Concentric live center [Morse taper #4]. Mine has tree bearings: 2 needle bearings support the rotating center radially, and one thrust bearing supports it axially. RADIAL LOAD: [1] The OD of the needle bearings is a light press fit into the center's stationary main body. [2] The ID of the needle bearings is a close, but sliding fit around the center's rotating spindle. AXIAL LOAD: The rotating spindle is supported at its rear by a stiff spring, and in turn this spring engages a 3-piece thrust ball bearing. Thus, the rotating spindle is free to compress into the stationary main body ... to a depth in which the axial force exerted by the workpiece is matched by the progressive resistance of the spring. Hope this helps a bit.

Mike Burdick
02-19-2005, 12:10 AM
Tom,

Yes it does!

The reason I'm asking is that I was thinking of building my own live center and was thinking of how it should be constructed in order to allow for work piece expansion. Having the bearing move was the only way I could think of to accomplish this.

By the way, would you mind posting those bearing numbers from the Concentric that you have apart?

Thanks...Mike

Tom CPM10V
02-20-2005, 12:23 AM
The original needle bearings were Torrington part numbers GB-1212 and GB-1112. I was unable to find a GB 1112 so I am using a regular B-1112. [The "G" identifies it as precision.]

The thrust bearing does not have a part number on it. It is approx .840" on the OD by .700" thick. Balls are approx .281" in diameter, and there are 5 of them. With some spacers, I'm sure I can convert to Torrington needle thrust bearings.
BEST WISHES, Tom

Mike Burdick
02-20-2005, 01:24 AM
Tom,

Thanks for taking the time to give me that information. I appreciate it very much!

- Mike