Dan Miller wrote:

Hey all,

I'm currently turning a piece of bar stock approx. 1.25 inch in diameter
and about 7 inches long between centers in my small Myford ML7 lathe. I
have it in a 3 jaw chuck and rotating center at the tail stock. Given
I've been taking relatively heavy cuts (for me that means 20 thou) but
I'm noticing that the diameter is roughly 5 thousands larger at the
tailstock end than at the chuck end. What's this mean to you guys? Do I
just need to move my tail stock over 2.5 thousands or could it also be a
twist in the bed or something? Thanks

Dan Miller
Seattle WA

I used to turn stuff held in a 3-jaw and a tailstock center a lot, then I
got in the habit of just turning between centers. It's the end-for-end swap
and the remove/replaceability I like. Also, you know the chuck isn't bending
your bar any. To get to your issue, I like to check lathe ways with a precision
level both ways. If it shows as level as you can get it then yes, just set over
your tailstock and be done with it. If your bed is misaligned you will get
similar error, yes. Make this part (by setting the tailstock to correct the
taper) and then recheck your lathe alignment.

The old way is still real good. Make a test bar to turn between centers (you
do have a drive plate and drive dogs, right?) with two collars, one at each
end. Take a very light finishing cut across both collars, striving for the
best finish, and take both cuts without touching the apron or cross-slide
wheels or adjusting your turning tool in any way, then measure the diameters
with a micrometer. If they show the same, you're home free. If not, adjust your
tailstock and repeat. This is the procedure from "How To Run A Lathe" and it
has worked for a long time for many people.

Grant