Reply To: Single Point Threading

[Bob Tascione]

Hi William,
Yes you can use a dead center in a chuck which in this case should work fine for you although it’s much more secure to use a center that fits into the taper in your tailstock or into one or more step up sleeves. This screw is so tiny though for your large lathe that the amount of pressure being exerted against the chuck should be negligible. For tool clearance you can grind a flat on your dead center shank for clearance.
Taking a series of really light cleanup cuts with a very sharp threading tool can sometimes solve the problem without using a center but you’ve most likely already tried that. Another thing that works very well and helps reduce deflection is to thread from the headstock out toward the tailstock. The tool is placed upside down in the tool post with the cutting edge set at center line and the lathe run in reverse. By cutting a relief a little less than the minor diameter of the thread into the stock just under the screw head you will be able to start the cut from the same point without digging into the steel. You would then run the lathe spindle in reverse. The result will be the same right hand thread. This is a technique used often in machining and is the way I usually do single point work. Without a mechanical disengage or kick out stop it is a less stressful way to thread (at least for me) as it almost eliminates the possibility of crashing into the headstock. I say almost because if an operator isn’t paying attention after stopping the lathe for a thread depth test and then re-starts the lathe in forward rather than reverse and kicks the thread feed in…well, surprise! There are other techniques that work well too but using a center is always a good way to go if you can swing it. This technique may seem complicated but thought I would throw it out there to show that there are other ways to do the same job. If you decide to experiment with this your tool post will need enough clearance to allow your threading tool to be raised enough to bring the cutting edge ‘up’ to the stock center.

Hope this helps William,
Have fun!
Bob