GETTING ON CENTRE
Whether you have a lathe with a fixed or a revolving headstock, it is most important to ensure that the head and the tail stock centres line up precisely whenever the tailstock is in use. If the tailstock is idle then it doesn’t have an effect.
This is borne out exactly in a recent little problem experienced by one of our newer members. He was having trouble with his lathe vibrating combined with the fact that the walls of the goblet that he was hollowing were of an uneven thickness. After suspecting the bearings might be worn but finding them to be quite alright, other reasons were looked at and it was found to be misalignment between the head and tail stock centres that was the cause.
While turning the goblet, the piece of wood was held in a chuck and supported by the tailstock while it was turned to the required diameter and roughly to shape prior to hollowing the end to make the goblet. Because the tailstock was out of alignment, it was pulling the wood to one side and directly it was taken out of use to hollow the end, the wood started to run out of true. This started the lathe vibrating and gave rise to the uneven wall thickness.
A simple way to check alignment is to revolve the wood (in a chuck) by hand and just touch the end of it with the tailstock centre point. If it is out of line, the centre point will scribe a small circle instead of making a dot.
Fred Harris.