Control Distortion of Wet-turned Bowls

[Darryl Fective]

I'm just wondering if others have attempted to control the tendency for a wet-turned bowl to become oval shaped. I'm often too lazy/impatient to twice-turn pieces, so I'm experimenting with some pressure longitudinally to counter the lateral shrinkage forces. It started with a piece about a couple months ago. I turned a thin bowl about 6 or 7" diameter. It was a Chinese elm blank that was very wet. As it dried it became very football shaped. I liked it initially, but I didn't like its new shape, despite generally really liking the warping and distortion that happens naturally. I put a pot of water on the stove and heated it up, not boiling, but maybe 180° if I'd have to guess. I put the bowl in and weighed it down and let it soak for a while. After removing it, it was very flexible and I put a couple rubber bands around it. It's dry and finished with a diameter varying by only about 1/4".

I just turned this one a couple days ago. It's a little over 1/8" thick, but has a thicker rim. (not sure if that's good or bad for this, we'll see) Anyway, I thought I'd try to monitor the dimensions and add rubber bands as necessary to keep it close to round. (keeping pressure against the rim on a flat surface would probably only invite splits) It was less than 1/8" this morning, so I added a couple more bands.

 

[robo hippy]

For me, the more they warp, the more I like them. As for controlling the warping, only really effective method involved slipping a round form over the outside of the bowl as it dries. Can't do it on the inside because your blank will split. Boiling might help, but again, you would need a circular form on the outside. My bowls are turned to slightly under 1/4 inch to maybe 5/16. Most of the time I will use the stretch film on the rim which is the most vulnerable part for cracks starting. They are done moving in maybe 5 days. You need a lathe that goes down to 15 or so rpm to be able to power sand and keep the abrasives on the wood.

robo hippy

 

[Leo Van Der Loo]

Wood shrinks and does not get shorter or longer.

The bowl you turned is getting narrower, making it appear that it got oval.

This once turned and dry bowl shows that the sides are lower and if you would pull the ends closer together, it would make that a lot more so, the second picture shows the sides up from a flat surface.




The eye gets tricked really like with this Walnut bowl, it looks really oval, but it is really still round.


It looks very oval, but it is still round.

 

[Don Wattenhofer]

Wood shrinks and does not get shorter or longer.

The bowl you turned is getting narrower, making it appear that it got oval.

This once turned and dry bowl shows that the sides are lower and if you would pull the ends closer together, it would make that a lot more so, the second picture shows the sides up from a flat surface.

View attachment 59968
View attachment 59969

The eye gets tricked really like with this Walnut bowl, it looks really oval, but it is really still round.

View attachment 59970
It looks very oval, but it is still round.

View attachment 59971

The one fact that Leo left out is that wood shrinks radially, tangentially and linear, with the linear being almost non existent so it is impossible to control it the way you propose. You might be able to control the oval by compressing the linear, it if you once turn green to a very thin wall but it would still be distorted in other ways. There is no point in trying to control the oval. There is one way to eliminate the oval, that would be end grain with the pith in the center but that leads to many other considerations to allow for the shrinkage that absolutely will happen.

 

[Jim Reynolds]

Side note: the wooden cowboy hat contingent are all in on controlling the shape of the "bowl" while drying. JoHannes Michelsen is an expert in the wooden cowboy hat arena. This is a link to his website. Perhaps he would share insights from his experience with you.

 

[hockenbery]

Side note: the wooden cowboy hat contingent are all in on controlling the shape of the "bowl" while drying. JoHannes Michelsen is an expert in the wooden cowboy hat arena. This is a link to his website. Perhaps he would share insights from his experience with you.

Totally agree but Johannes is bending the wood in the direction it wants to go.
@Darryl Fective is trying to limit the natural warp.

 

[Richard Coers]

Side note: the wooden cowboy hat contingent are all in on controlling the shape of the "bowl" while drying. JoHannes Michelsen is an expert in the wooden cowboy hat arena. This is a link to his website. Perhaps he would share insights from his experience with you.

Johannes doesn't control the movement, he increases the movement to get an even more oval form to fit the human head.

 

[Don Wattenhofer]

Johannes doesn't control the movement, he increases the movement to get an even more oval form to fit the human head.

In other words he is not making hats for Charly Brown Wops that would not work anyway, because there is not shrinkage linearly so you can't make a round hat.

 

[robo hippy]

I had a madrone bowl that came off the lathe at 22 inch diameter. When it was done moving, it was 25 by 19 inches.

robo hippy

 

[Leo Van Der Loo]

You know what they say "No picture, it didn't happen ;-))"

 

[hockenbery]

madrone bowl that came off the lathe at 22 inch diameter. When it was done moving, it was 25 by 19

know what they say "No picture,

I’ve done just a handful of green madrone turnings
Fun to turn, shavings could be a mile long they streams off and fold up on the floor.
They break when you pick them up.
These I did with a tool finish then when dry sanded lightly with 400 to remove the fuzzy feeling
These are little guys 5” diameter

Hour or so off the lathe

A day off the lathe pretty much dry

In a group lower left. A lot more interesting than when it came off the lathe.

 

[DON FRANK]

Several years back a made a framework to try to restrict the movement and all that did was make bowls crack. I tried them boiled and unboiled and had the same results with both. If it wants to move it's gonna move.

 

[Don Stephan]

For me, a warped bowl is most honest to the nature of wood. But warped bowls take much longer to sand, and not for everyone.

 

[robo hippy]

Leo, that bowl is shown in a video I did about cutting up logs for turning. Maybe I can find that one....

Found it, at about 6:30

robo hippy