Problem returning bowls

[Griesbach]

I recently started returning some cherry bowls that I roughed out last winter. However, they are not working out and I've had several that broke through the sides and one that blew up. (It wasn't cracked) They run from 6" to 12" dia and 3" to 6" high. They warped and average of 5/16" out of round but were not much over 1/2" thick on the rough turning. I suspect that I failed to leave them thick enough when I first roughed them out.

Any advice for the future and help on how to deal with the remaining rough outs will be appreciated.

 

[Ed Koenig]

My rule of thumb is anything up to about 12" should be left 1" larger or 13". After that, add 10% to the finished size. ie; 18" should be ruffed out to about 19.8" Once you know the characteristics of each wood, you can alter the thicknesses accordingly.

Ed

 

[Mark Mandell]

I recently started returning some cherry bowls that I roughed out last winter. However, they are not working out and I've had several that broke through the sides and one that blew up. (It wasn't cracked) They run from 6" to 12" dia and 3" to 6" high. They warped and average of 5/16" out of round but were not much over 1/2" thick on the rough turning. I suspect that I failed to leave them thick enough when I first roughed them out.

Any advice for the future and help on how to deal with the remaining rough outs will be appreciated.

Cyril,

If you're going to be twice-turning bowls, the general rule is to have wall/rim thickness on the rough-outs at at least 10% of the diameter; sometimes a bit more with wood that deforms a lot during drying. Thus 1/2" would be too thin even on your 6" bowl. Since cherry, like most fruit woods, usually has a fair amount of compression wood and is known for its "dancing" ability, you'll do well to leave it heavier still. Any rough will go "oval" during drying, and if you want to get really technical on the subject, the USFS Wood Handbook will give you forumulas and precise deformation and dimensional shrink rates.

Also make sure that your wall thicknesses are even; leave heavy walls but a thinner bottom and you'll have an "design opportunity" and practice of your inlay technique.

A 6" cherry rough should be cut to not less than 3/4", and a 12" bowl to not less than 1-1/4".

Better Luck with the next batch.

Hey, it's how we all learn.

M

 

[-e-]

additionally, fruit woods are excellent boiling candidates.

 

[Joe Fisher]

additionally, fruit woods are excellent boiling candidates.

I prefer mine barbequed. Maybe a nice spice rub, or a marinade.

I agree with the other posters; sounds like your rough-outs were too thin. A rough wall thickness of 10% of the diameter seems to be the accepted norm.

Good luck!

-Joe

 

[Griesbach]

Thanks for confirming my suspicions, guys. The cherry is the hardwood variety not fruit wood. I still have some left so I'll try again. I guess I just couldn't stop the fun of all those sweet ribbons of wood sailing off the gouge .

 

[MichaelMouse]

Well, without being there, I'd say that if you were a fat half inch, you should still be able to do ~1/4" thick walls on a 10 inch or so bowl. You can take a look at what your fellow cheeseheads have worked up as averages for P serotina at http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm chapter three. Tangential 7.1% shrinkage radial 3.7 from FSP to bone dry. Means you should leave about 5/16" over your desired wall thickness for a rough for a 12" bowl. On average, take your desired final thickness and add half your tangential shrink. Any more will give you some redesign capability, but will take longer to dry, as well.

Where folks get into trouble, often, is in centering for re-turning. Not sure if this was the case for you, but I find it convenient to leave my original pin chuck opening for re-use when the piece is dry. I drop the 1" forstner down the hole and mount same way as when I originally turned. The piece is symmetrical that way, so I only have to take off the end grain until it matches the longto regain circularity.

Snapped a picture of a couple of cherry chunks from my basement. Three views of one for you. Note that part of the 1/2" loss is not really a loss, because the outside edges have dropped a full 1/4", and with the slope of the sides, that accounts for over an eighth.

 

[RonW]

I have trouble turning dry cherry for bowls. In my case I soaked blanks in alcohol and let set out to dry for several weeks. When I got back to two blanks, they were terrible to turn even with newly sharpened tools. One bowl blew up on me, which kind of wizzed me off a bit. On the bright side, I got to see how evenly I was turning the walls. As someone said above, live and learn.

Ron Wilson

 

[dkulze]

I'll go Michael one further. If you rough between centers and leave that cone in the middle, it will remain centered and, when dry, you can remount between centers and turn a nice little tennon on the bottom with no prob. Friend taught me that trick and it works well.

Dietrich

 

[Griesbach]

Thanks for all the help, guys. Live and learn . Michael, the link is invaluable, stored in my favorites. The forest products lab is only 100 miles south but they don't accept strangers very well (I'm told, by my forestry friends) . I retired from a career in natural resources, LE aviation, former state chief forester a personal friend - still can't get in . Maybe I smell like concrete .

I shall continue to learn (even by trial and error) but thankful for all the help and friendly information here at AAW.

 

[Ken Grunke]

Try soaking a blank in water or even boiling it, it may "unwarp" itself somewhat so you can turn it before it drys again. Worth a try, I think.