This moldy-oldy still works. I didn't write it, but I also don't remember where I got it other than to say it was a reputable source or I wouldn't have saved it.
To check the alignment of your headstock and tailstock, insert a live center into the tailstock and a 8spur drive into the headstock. Make sure that the points are not dulled or bent in either the spur or the live centerâ€"this will mislead you in your measurement. Bring up the tailstock to within 1/4" to 1/2" from the spur center, then tighten down the tailstock and quill. Now, observe the alignment of the two points. If the points are misaligned, you can compensate by placing a shim under the appropriate corner(s) of the tailstock to adjust the alignment. Often a sheet or two of paper will be adequate to shim the tailstock. For more exaggerated errors, contact the lathe manufacturer for repair or replacement of the tailstock or tailstock quill. An extreme case may require reboring of the Morse taper on the tailstock quill. If the lathe headstock is bolted to the frame or ways as with the Jet mini-lathe and Delta Midi, you can realign it with the addition of a permanent shim under the appropriate corner. On other lathes such as the Oneway, for example, you can align the headstock by adjusting the jack screws provided for that purpose. If you own a Nova 3000/DVR, you can reposition the lathe ways themselves, as they are screwed to the headstock unit. Be sure to follow the instructions in your owner’s manual for all adjustments noted above. On lathes with a rotating headstock, the click stop positioning may not be accurate enough to return to perfect alignment. A double-ended Morse taper will aid in regularly realigning the headstock each time it is moved. These are available from Lee Valley.