Apple!
sjBrian said:
my faceplate has been centered and flush with the wood. i think maybe it is the way i hold my gouge. the first piece i turned was a small spalted maple blank. it came out fairly nice. my second piece was a large spalted apple blank. that one became off center.
my tools came with a small pen turning lathe i got a few years ago. would bigger tools make any difference?
Bigger tools WILL probably help, the mass makes them bounce less on the tool rest, BUT...
The probable culprit here is the wood itself: Unlike metal, which when properly mixed, is of an even consistency and weight, wood density (weight) OFTEN varies from one part to another...
Wet wood has the most chance to travel. I have seen a 5 inch thick slab from many straight logs bow up MANY inches when cut. They can look like rocking chair bases. That indicates a lot of stress in the wood, so when you try to turn it, the stress is released and "reshapes" the turning.
Also, sap wood usually being lighter and softer than heart wood, for instance can cause pieces to shift if the wood is not all one or the other. Branches and crotches also change the density of the area that they are in, so - even what appears to be an "ordinary" piece of wood can hold significant surprise.
Then you add in the spalting factor, which is yet another opportunity for the wood to work against you. More decay in one area than another can make things out of balance too. The wood itself could be unbalanced and fighting to find it's own center, which could cause the lathe to "vibrate" and cause the light tools to skip which would cause the piece to go off round.
AND, as the edges get thinner, the stress in the wood might be strong enough to push the edges out of round. Unlike a block of metal, the stress of growth is inherent in the wood. That stress could work against you as well.
FURTHER (and most probably in this case), apple distorts like CRAZY, almost all of the time.
So, you might have a perfectly round piece, go in for lunch and come back to an oval... and the thinner the turning gets, the faster the water comes out and the faster it distorts.
Always coat or cover a piece you are working on when you leave it, otherwise you could come back to BIG cracks (I learned that lesson the hard way, and it ain't pretty).