Iggy,
Please find my old response to this procedure. The following sequence is essential.
1) mount test bar into spindle. Spin it to verify it is centered. (no tail stock)
2) use the indicator on the horizontal axis and measure change parallel to the bed by moving the carriage.( Record the readings if
not 0)
3) repeat number 2, but with the indicator on the top of the test bar (vertical axis)
4) if these results are not 0, the head stock must be aligned with the bed with shims. This is very simple to do, but not
necessarily easy. Removing the gear box and drive will be required.

Remember, the most important adjustment is the bed itself. To do this, you must have a precision machine level. This must be done
over a one month period, especially on a large heavy machine. Lathe beds are like a big heavy piece of rubber and they twist very
easily. Follow these steps.
1) level the bed front to back at the head stock end placing the level on the bed at the head stock
2) adjust the bed level head to tail stock with the level on a machine bed flat front or back side doesn't matter.
3) check the bed level front to back at the tail stock end. if the bed is not level there and the bed is still level at the
headstock, you have bed twist.
Be prepared to adjust and readjust through several iterations before you are happy with your findings.

If you have twist, you must counter twist the bed straight. Once that is completed, be prepared to check the set after a few days
and repeat again 'till straight. This can take up to a month to get the set stable. If this is a large machine without a cabinet,
this can be done with the adjustable feet alone. If the lathe bed mounts on a cabinet, remove the bed mounting bolts at the tail
stock end, jack the bed up a bit and shim to suite, until straight. I often drill and tap the bed feet and use a screw to twist
the bed straight, then use feeler gauges to determine the shim size. Then backing off or removing the jacking screws
afterwards.You may note that when measuring for twist that the bed appears to sag in the middle....they do..... it's normal. You
my also find that the bed dynamically twists with the carriage motion....again this is normal. The carriage is front heavy because
of apron weight. My 13 x 40 SB twists.002"in the middle with the carriage centered.
Steve


"Ignoramus2532" wrote in message ...
I bought a "test bar", which is a 10" or so long with MT3 end.

I inserted centers in the headstock and tailstock and mounted the bar
between those. Then I aligned tailstock with headstock, such that the
position of the indicator was the same at both ends.

This gave me about 6 inches of travel along the straight portion of the
test bar.

The good news is that the travel of the indicator, as I moved the
carriage from one end to another over 6 inches of distance, did not
seem to exceed 0.0003" or so.

Of course, aligning tailstock using position of carriage as a
reference, and them measuring deflection of the indicator on carriage
using the bar as reference, is a little bit "self referential".

In other words, the indicator does not really tell me if the carriage
moves parallel to the imaginary axis of the spindle rotation, because
that axis was not used in any way. But what the indicator does tell
me, is that along those 6 inches, the carriage moves on a straight
line.

That is already something and is much better than what happened with
my old lathe, where the carriage moved along a jumpy line (as
evidenced by abrupt changes in thickness of a test cut).

I will try to do more measurements.

i