To hold the centerline on the workpiece will help the device shown in the figure.
Recommend to read
GEAR RACK ON THE LATHE
We offer you a simplified method of manufacturing a cylindrical gear rack. It can be done with a conventional tap, picking up the thread profile in accordance with your existing gear....
RIDING ON THE VACUUM CLEANER…
Not so easy to store a bulky vacuum cleaner in a small kvartire. Meanwhile, it is quite possible to "hide" so that it did not occupy a special place. For example, it is very convenient...