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Do you lap your female centres ?

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awemawson:
I've been doing a bit of between centre turning and cylindrical grinding recently.

Now obviously you need nicely formed centre holes for the work to run nicely - I've always just very carefully drilled my centre holes with a centre drill aiming for the best  finish I can get, but I'm aware that lapping the centres is recommended for precision work.

So do you lap your female centres, and if so how do YOU do it ?

chipswarf:
In 1969, at the USAF Machinist's Course at Chanute AFB, IL, the grinding shop had a center lapping machine. It was set up like a drill press, with some sort of chuck holding a rod shaped stone in line with a static center on the table below. There was a rickety appendage that could be swung into place to move a diamond tip in a 30 degree angle to the vertical chucked stone. Thus, was put a 60 degree cone point on the working end.

After 'truing' the stone point, you'd settle one end of the workpiece into the lower static center and run the turning stone point into the top center. All this story telling is by way of suggesting how you might set up your own center lapping device.

chipenter:
Only on stuff that has been hardend and quenched , on softer metal I stop feeding the center and hold it for a few seconds .

leg17:
Center Lapping
As mentioned above, center lapping is for hardened materials, typically for grinding operations.
Abrasive center laps are relatively inexpensive.  They usually are available in a couple of grits.  A medium or fine grit will usually work on properly drilled workpieces.  Chuck the lap in the headstock of your lathe.  Install a conventional center in the tailstock.  Carefully position the tailstock so that the workpiece can be held against the tailstock and not accidentally break off the tip of the fragile center lap in the headstock.  Turn on the headstock, maybe about 500 rpm or so.  Hold the workpiece against the tailstock with the left hand and center it as well as you can.  Advance the tailstock carefully until the lap engages the workpiece.  You will hold the workpiece against the tailstock center to prevent it from turning AND to prevent the weight of it to damage the center lap.  Gently make contact with the lap to clean up the workpiece center.  This should not take much effort if the center hole was carefully machined prior to heat treat.  Be careful backing away so as not to damage the lap.  Reverse the workpiece and repeat.
The lap rotates, not the workpiece.
The lap usually will not be able to bear the weight of the workpiece.
Work carefully.
Let us know how it worked out.

ian99:
Great title for a thread and I was hoping for some pictures. But I guess I have a dirty mind!

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