To hold the centerline on the workpiece will help the device shown in the figure.
Recommend to read
DOOR INSTEAD OF DRAWERS
Plastic drawers commonly used in modern domestic furniture have a long life. After a few years of service, they warp, can't move on rails, and then crumble. Do the drawers only...
IN THE LANGUAGE OF DOTS AND DASHES
It's tempting to assemble a simple Telegraph device and to communicate using Morse code. Reliable two-way communication is needed in the conduct of military sports games and...