I concur that a live center is preferred, but a cup center is still useful. The keys to using a cup center are:
Use a non-metal mallet to drive the cup center into the end of your stock. Make sure that the outer ring of the cup is at least slightly impressed into the end of your wood stock. If you fear that the center is going to split your wood you can use a drill to create a shallow hole prior to driving the center into your wood. Drive the drive center into the opposite end and if you like, hammer both centers into both ends. I do this so I can flip the spindle end for end during sanding.
L to R Shopsmith Live, Cup and Drive Centers
- Add a little dab of paste wax to the cup. This step is often skipped, but a little furniture paste wax is a big help. Use Johnson's or Minwax or Brewax. The brand doesn't matter, just don't use car wax.
- Insert the cup center into the tailstock and the drive center onto the drive spindle and insert your wood between the centers. Put just enough pressure onto the wood with the quill that the wood is trapped, but not clamped between the centers. There should be no end shake or play, but the tailstock shouldn't be under stress.
- Turn, turn, turn, turn but keep an eye and ear on the cup center. It will beige to loosen due to friction, so every so often turns off the lathe and double-check the tension between centers and if needed adjust the quill out to increase the tension.