bulging bowl bottoms

"TWW" wrote: (clip) The

^^^^^^^^^^^^^^^^^^^^^^ I believe that is the reason the bottom is usually turned concave. Wood moves, even after it is seasoned, as temperature and humidity vary. If you left the bottom thicker, and then resanded every time the bowl started to rock, you might eventually reach a condition where it changes from concave to flat instead of flat to convex.

When you turn an endgrain bowl, the diameter of the bowl is fairly stable, but greatest warpage is in the direction of top to bottom. In your case, the bottom of the bowl warped outward giving a bulge on the bottom. Regardless of the grain orientation, it is always desireable to recess the bottom of the bowl so that it will set only on the outside edge of the bottom. This helps reduce the possibility of the problem that you had and generally makes a more stable bowl. Some woods warp more than others. Had it been something like black locust, there is a chance that it would not have become bulged on the bottom.

Fred Holder

It warped that way because of grain orientation. On bowls turned with the pith on the top rim of the bowl, and the bottom of the bowl is on the outside of the tree, the bowl bottom will go concave as it dries. When the bottom of the bowl is towards the pith, it will go convex (or bulge). The interesting thing is that if you get it wet again, it will warp back the way it was before it dried. They will always move some, because that is the way wood is. It will change due to humidity variations because it soaks up some moisture. This is pretty much the way boards dry. Cut a flat board off the outside of the tree, and it will warp/cup away from the center of the tree.

robo hippy

Sounds like an end grain project, as opposed to cutting a "normal" cross grain blank?

You're turning green wood here.. the 3 months changed them (in my terms) from WET wood to Green wood.. Sill going to have movement.. In an cross grain bowl, it will warp "egg shape", like a banana split dish.. The way you turned yours, the warp will mostly be in the bottom..

I usually leave enough wood at the bottom of the bowl so that when I reverse it to finish the bottom, I can dish out the foot.. Might have helped in your case, but not sure with out pictures..

Bottom line is: Did you enjoy the experience and want to turn some more? If so, it's a winner, right?

mac

Please remove splinters before emailing

in addition to what everyone else said, I find that oak does this a lot - so either feature it (and turn thin to avoid cracks) or do as others suggested and plan for it.