Thread: Turning between centres ?

Mike, you can turn it to an accurate size using a 3 jaw or 4 jaw chuck - it's just that as soon as you take it out of the chuck there is a lot more trouble getting it bang on centre again.
A mandrel will do the job, but usually have a very fine taper to lock on the part being turned (from memory I think it's something like 5 thou per foot). Therefore you need to be able to accurately turn the mandrel to a few thou as well as cut a very fine taper.
Accurate has a whole variety of meanings too, but my first thought would be to chuck it up in a 4 jaw chuck, as if you turn half to size you should then be able to reverse it and get the other half concentric within a thou with relative ease - would that be good enough? (depending on the chuck and lathe you could probably do better, but it will take longer).

Michael

Another option are the expanding mandrels from machine tool suppliers. Just throwing it out there.

If you mark jaw position on the piece before taking it out of the lathe and then using the tailstock as a "press" to evenly push it whilst refitting and slowly tightening the chuck you can get within 1/2 to 1 thou quite quickly. This will not work well for scaled, rusted or otherwise rough bar to jaw contact. Jaw -job contact surface needs to be on clean bar. And also gets damn difficult for small thicknesses, ie thick washers or spacers.

Are you trying to turn the OD of the solid piece to suit the bore?
If so why not mount the piece of bar and drill it to suit a bolt,then put the bolt through the hole,tighten the nut and place this back in your lathe chuck so you can turn the OD.
Any reason why all the keyway has not been removed from the outer ring.

Originally Posted by pipeclay

Are you trying to turn the OD of the solid piece to suit the bore?
If so why not mount the piece of bar and drill it to suit a bolt,then put the bolt through the hole,tighten the nut and place this back in your lathe chuck so you can turn the OD.
Any reason why all the keyway has not been removed from the outer ring.

That's a good idea , the centre bush has now been bored to accept a bolt or a mandrel as the case may be . Yes there is a small section of keyway still there . I didn't want to make the bore any larger as the piece of scrap I found for the centre bush is just large enough at the OD to fit in the bore , by about 1/16" . MIKE