Hi Nige

The classic method, if I understand the request correctly (Saturday night wine, not your description) is to use a dial gauge.

So hold a parallel in the vice jaws and set up a stationary dial gauge touching it, perhaps by putting the magnetic base on the lathe bed.

There is a theoretical error in that all lathes are supposed to face very slightly concave on extremes of tolerance, but hey, it's only small.

You need to clamp the casting to the cross slide with Tee bolts and clamps etc. and tap the casting progressively to true it up. Bit of a chew, but the only way.

It will take a lot of time to fly cut that lump off with the lathe.

Good Luck – Will

If you don't have a clock gauge, how about chucking a good piece of bar in the 3 jaw, or even better turn a bar parallel between centres. Then clamp the base end of an engineer's square in the machine vice at centre height, offer the blade up against the captive bar, and nip up the clamping bolts when it's parallel.

… and when clamping your parallel in the vice, put a piece of round stock, say about the size of a pencil, between the moveable jaw of the vice and the parallel. This will ensure the parallel is pushed up against the fixed jaw and give a true reading of the position of the fixed jaw. Otherwise, the moveable jaw can tilt out of square vertically and allow the parallel to sit not quite dead true to the fixed jaw.

Hi

I guess the question really is how do I align the vice fixed jaw to a plane at ninety degrees to the axis of the spindle. The alignment of the vice jaw must be both vertically and horizontally in line with the plane. The plane will later be the path swept by the cutter or fly cutter.

On method that would work quite nicely would be to remove the 3 jaw and replace it with a face plate assuming you have one. You could then fit a dial indicator or pin with a rounded end on the face plate at the diameter that allows the measuring device to clear the vice as it is swept, A small bracket or fixture made from scrap maybe. to hold it.

If you don't have a face plate then make up a crank and fit that in the 3 jaw, attach the indicator to that.

If you don't have an indicator a piece of feeler stock could be used to check the gap at the end of the pin, testing at various positions for a similar tension.

You will also need a piece of material of known flatness to fit in the vice jaw Long enough an wide enough for the indicator to run on over its sweep of 180 degrees.

Maybe a piece of polished kitchen stone ofcut or plate glass lightly clamped in the vice if there is not a flat surfaced object to hand. I would put them between 2 pieces of copy paper to reduce the chance of cracking, unless the job required super accuracy. Modern papers are pretty even.

This method cancels out any error in your face plate because you are measuring 2 points at 180 degrees
Three points if your flat surface is wide enough to check against it at 90 degrees.

So your vice will be aligned in 2 planes.

Regards
John

Howard that is what has been said above, first by me, 2nd by Martin and then by Phil