Turning a spacer

[jcfx]

I have a spacer that I'm making so that I can do some machining on a chuck backplate installed backwards
on my lathes spindle, the spacer is 2" OD with a 1.50" bore .25" length, so it's basically a ring.
it;s been bored to size and I need to part this off the short billet, and based on my previous experience
parting on a lathe I know the parted off piece will not be dead nuts square, which I need it to be.

I've been eyeballing a small round magnetic chuck, I can part off the ring knowing that one face would
be used as my reference surface and I would use the mag chuck to hold the work to true up the
parted face, since there's not a lot of material to grip on a ring that's .25" thick.

Any suggestions on how to true up the parted piece ?

[Harold_V]

One thing you might consider doing is to partially part the piece, slightly longer than the finished size. When you have the parting cut deep enough to allow a cut, face the side you'll keep, so it's dead parallel with the work. Finish parting, returning to the parting location, avoiding the area you've faced, then you can dial that surface true for a finish cut. If you finish rough facing the parting cut before taking the entire face to length, you won't even have a witness line.

You make no mention of your capabilities, but this is a good example of the benefits of using soft jaws. Properly machined, they'll yield dead parallelism, and eccentricity no greater than five tenths.

H

[Dave T]

Do you have access to a surface grinder ? I would consider grinding the magnetic chuck first.

[Magicniner]

If you pilot drill the part you can machine both faces then bore to size.

[jcfx]

Harold - as you suggested that was my intention, but I got stingy with cutting the 4130 steel rod so it's too short to part at this point
so I'm shimming the part out off the face of the chuck. Unfortunately I do not have soft jaws nor the possibility of adding them because
my chuck has solid jaws not two piece.

Dave T - I wish I had access to a surface grinder, that's a big reservation I have about buying a import mag chuck
there's no guarantee that the base and the face of the chuck are dead parallel to each other.
US made chucks are out of my price range and they're too big.

Magicniner - I did pilot drill the blank, the initial hole is thru but the succeeding holes were not because
I was going to bore to a depth not all the way thru. one face and the bore is machined, but you have me thinking I might be able
interference fit a aluminum rod into the bore so I gain a little more chuck grip to part the piece.

[johnfreese]

Chuck up a piece of bar. Face it off. Attach the spacer with cyanoacrylate glue. Face the spacer using light cuts. Use heat to remove the spacer.

[jcfx]

I chickened out of parting it off on the lathe, I had too much chatter probably from not having enough
material to grip. I wound up using a piece of 1.5 of aluminum rod, as a mandrel and
carefully clamping and cutting it on the bandsaw ( 3 cuts, not thru ) and finished the cut with a hack saw.
Then it was back to lathe to face off the gnarly bandsawed face, I was surprised to get
really close, I used the face of one of the jaw steps as a reference surface.
Dead nuts on in the thousands, but varied about .0002 in the ten thou range.