Bowl Warpage --- What Happened??

[Doug M Jones]

I roughed out a thorny locust bowl about 6 weeks ago, soaked for a day in DNA and then put in a brown paper grocery bag to dry per all the instructions I have seen on the web. I checked the weight every few days and when the weight hadn't changed in 3 weeks thought it was safe to turn. I probably left the sides a little narrow when I roughed it out but was able to turn a nice round bowl with about 3/16" sides. Looked really great at this point. I put the sanding pad in the drill, slowed the lathe to it's slowest setting and started to sand. Tried to keep nice light even pressure. After sanding through 180, the bowl was not even close to round anymore. Did the heat from sanding warp the bowl? I tried to bring it back to round with the bowl gouge but ended up with an exploding bowl when one side became too narrow. Any help you can give will be greatly appreciated.

[Bernie Weishapl]

Doug most times when I rough a bowl I leave the sides at least 3/4" thick and no less than a 1/2". On bigger bowls the walls are 1" or thicker. 3/16" doesn't leave you much to work with. By the time you take a 1/16" off the outside and 1/16" of the inside it doesn't leave much. I did the same thing on one of my first bowls.

[Patrick Taylor]

Even after the blank is dry, there are still residual stresses in the wood. When you turn away more wood, those stresses can cause the wood to move a bit more. If that's the case, there's not a whole lot you can do besides sand carefully. When I get movement after final turning, I usually sand the best I can on the lathe's slowest speed, then stop the lathe to sand out the missed spots, then sand with the lathe on slow again to even out the sanding marks, then stop it to make sure there are no tool marks left, etc. etc.

Maybe someone else has some experience with that species? I don't know how much movement to expect with it.

Also, maybe your bagging job was too good at insulating the piece, and it stopped losing weight but was still wetter than the shop air?

Sorry about the explosion! :(

[Bernie Weishapl]

Just a another note Doug on what Patrick said. I wrap my bowls like a Christmas present after doing the DNA soak. Then I cut a opening out to the rim inside the bowl making sure the rim is still covered. I then turn it upside down on a drying rack or cooling rack you can get from Wal-Mart for a buck or so. I also have them drying in a place where it is cool and not much air flow.

[Sean Troy]

A good rule of thumb that has seemed to always work well for me is rough turn the piece to 10% thickness of the diameter.

[Frank Kobilsek]

Doug

Another issue is consistent thickness in your roughed out bowl. If you have 3/4 wall at the rim and 1.5 thickness in the bottom you'll have more troubles with warping and cracking. This is true regardless of drying method.

Frank

[Ken LaSota]

Doug the thing I learned from Bill Grumbine's dvd is that you leave the sides 10% of the dia. and make the bottom less . If they do start to warp after th final cut they become art and good conversation pieces. I have many that have contorted after the final turn and finish but don't go back to the lathe.
Ken

[William Bachtel]

Locust takes longer to dry than 6 weeks. Unless it was in a kiln. You proably had a little stress and a little moisture. I wood have sanded it, and finished it, and noone wood have noticed, wood is a living, thing and will always move, from time to time.

[Al Wasser]

I don't turn much green wood, mostly dry. Believe me kiln dry wood moves. I have figured out that once you start a bowl, finish it. Don't do part today and part tomorrow. I trurned one a while back, and after sanding etc, I decided I did not like it. SO I thought I would rework it tomorrow. Tomorrrow I turned the lathe on and we had a big time dancing bowl. So it got a coat of finish. Wood just has stresses in it and when you remove part of the wood, green or dry, those stresses change and the shape changes - some pieces more than others

[Bob Hovde]

Some wood moves very little - some moves a lot, no matter what you do. The moving wood is best turned all at once, left alone and promoted as "art."

Bob

[Doug M Jones]

Sorry Bernie, I wasn't real clear. I left the sides about 1/2 inch when I roughed it out and took it down to 3/16 with the finish turning. After DNA, I put it in a single grocery bag, cut out the mouth of the bowl and set it upside down on the rack to dry.

Frank,
You may have hit my problem. Two things, I went to the burn pile and pulled out the projectile and noticed that I left the bottom about 5/8" thick when the sides were 3/16. Also, I don't have a chuck yet so I glued it to a block to attach to my face plate for roughing out. I soaked it with the bowl and left it attached to the bowl while drying. In essence, the bottom of the bowl including the glue block was 2" thick. I did an oak bowl last week and noticed that it moved a tiny bit after I parted it off from the glue block.

Guess I need to point LOML and the kids toward a chuck for fathers day. Our 30th wedding anniversary is the day after fathers day, I've got a really nice anniversary ring picked out for Cindy, I suppose a chuck would not be romantic.:p

Thanks for all the great advice.