Mike you could try Cowells Lathes as well, Alan

Hi Mike

If you have a three jaw chuck and a dial indicator together with nice piece of ground bar maybe 300mm long you can use that for testing.

Just put it in the three jaw and by rotating the spindle with the indicator set on the saddle and on the top of the bar on centre take the two measurements on you indicator at a few places along the bar say every 5mm find the highest and lowest points and write them down then subtract the low reading from the high reading and record the difference. If the bar is not exactly on the spindle axis it does not matter we are nulling the error out.

This will determine if the machine axis is parallel to the bed in the vertical plane. You should allow for sag… Here is a few articles. **LINK**

You can do the same on the side of the bar at 90 degrees to the vertical plane again (and on centre) find the two extremes on your indicator. and record the three values as above.

If you put the results of your measurements in Excel you can graph them, It should generate a reasonably straight line if your lathe is in good condition. Bear in mind this test is checking the relationship of the saddle to the bed against the headstock axis.

Ideally the result should be two flat straight line graphs… Or (At the risk of starting old argument among members) Pointing a couple of tenths up and forward towards the operator at the end of a 300mm bar. Not easy to set up.

The ground test bar must be the same diameter along its length and truly round, This can be checked by placing it in a v block and measuring it using three points. Remember measuring a bar with a mike at two points is not a test for roundness.

If you do decide to purchase a taper test bar it will almost certainly not be concentric with the axis of the headstock spindle. Particularly if the lathe is an older machine, tapers get damaged and bearings wear.

The method above will correct the errors if you do decide to purchase one.

Regards
John

Edited By John McNamara on 09/12/2013 07:52:25