Successfully drying rough bowls: Is there a tipping point in terms of diameter?

[Rip Littig]

Recently I've been chainsawing large bowl and platter blanks from black walnut trunk sections (25" total diameter; 20" heartwood). After rough turning and coring, the largest bowl is 20"+. Using the 10 percent guideline, wall thickness is 2" or more. Regardless of using paper bags, sealer or another method to prevent cracking, is there a diameter where you start to lose significantly more stock? I'd rather find out now vs a year or more later. I understand few people want finished bowls anywhere near 20". My intent is to donate them as auction items for nonprofits events, etc. If I'm likely to lose a large percentage of these bowls I'll start with smaller blanks and be content with a diameter that is much less prone to cracking. Thanks in advance for any words of wisdom!

 

[Dennis J Gooding]

I do not have much experience with large walnut. Have you considered boiling the rough turned bowls before drying?

 

[Rip Littig]

I haven't, though that's a good suggestion for proving extra protection from cracking.

 

[Richard Coers]

Absolutely not. Walnut dries incredibly easily, but if you include wet sapwood or crotch figure, there is no predicting the wood movement. I once turn 18" soft maple bowls all the time, with little to no loss.

 

[JeffSmith]

I just roughed and cored some walnut I got through the local club. Boiled it and it’s stacked for drying now - don’t anticipate any problems so far , but it’s going to sit on the shelf for a few months before I look at it again. I skipped boiling some NW Bitter Cherry I roughed a few months ago and am paying the price in platter blanks that are going to the firewood pile. Bowl blanks have been better behaved so far.
I usually plan to boil any fruit woods or walnut I get. The big leaf maple and alder that often comes my way seldom requires boiling so I get out of practice…until the price needs to be paid.

 

[Rusty Nesmith]

Recently I've been chainsawing large bowl and platter blanks from black walnut trunk sections (25" total diameter; 20" heartwood). After rough turning and coring, the largest bowl is 20"+. Using the 10 percent guideline, wall thickness is 2" or more. Regardless of using paper bags, sealer or another method to prevent cracking, is there a diameter where you start to lose significantly more stock? I'd rather find out now vs a year or more later. I understand few people want finished bowls anywhere near 20". My intent is to donate them as auction items for nonprofits events, etc. If I'm likely to lose a large percentage of these bowls I'll start with smaller blanks and be content with a diameter that is much less prone to cracking. Thanks in advance for any words of wisdom!

I have never lost anything no matter the size when sealing with green wood sealer and putting on a shelf. I lost quite a few using the brown bag method, that is why I switched.

 

[Lou Jacobs]

Absolutely not. Walnut dries incredibly easily,

I agree with Richard. Walnut I’ve worked with has been consistently easy to dry without mishap.

 

[hockenbery]

Walnut wood shrinkage is 5.5% radially and 7.8% tangentially these are pretty close making walnut one of the least warping woods in North America.
Hemispherical bowls with even walls will dry with a high success rate.

Compare to madrone which is famous for severe warp radial 5.6% and tangential 12.4%

Bigger issue with walnut is ring shakes. This is a preexisting separation around growth rings.
I’ve found ring shakes in quite a few walnut.

 

[Leo Van Der Loo]

I've turned quite a lot of large bowls from green wood, dried in my Brown paper bags, I don't remember a single one that split drying them that way.

Brown craft paper can be used instead of a bag.

Here a couple of larger pieces that I have turned.

Large Honey Locust.



Large Maple bowl.



Black Walnut bowl.



Large rough turnings

 

[Rip Littig]

Walnut wood shrinkage is 5.5% radially and 7.8% tangentially these are pretty close making walnut one of the least warping woods in North America.
Hemispherical bowls with even walls will dry with a high success rate.

Compare to madrone which is famous for severe warp radial 5.6% and tangential 12.4%

Bigger issue with walnut is ring shakes. This is a preexisting separation around growth rings.
I’ve found ring shakes in quite a few walnut.

Thank you Al. Does this stability mean I should rough turn larger walnut bowls to < 10% thickness?

 

[Rip Littig]

I've turned quite a lot of large bowls from green wood, dried in my Brown paper bags, I don't remember a single one that split drying them that way.

Brown craft paper can be used instead of a bag.

Here a couple of larger pieces that I have turned.

Large Honey Locust.

View attachment 61296

Large Maple bowl.

View attachment 61298

Black Walnut bowl.

View attachment 61302

Large rough turnings

View attachment 61303

Leo, you never cease to amaze me with your knowledge and talent.

 

[John Grace]

I've tried all of the above but then just became a bit lazy. Rough turn my pieces to 3/4" to 1" wall thickness, slather it in anchor seal, set on the shelf for 8+ months to finish drying. I've never 'lost' a piece of walnut or maple to cracking...ash and white oak, yes. Depending on what my wood supplier gets me...I will frequently start a piece with an eye towards how much heart is left on the blank being sure to cut that away first and foremost. What I haven't seen mentioned above is subjectivity relative to shop conditions and geography. Turning in an area with lots of humidity is going to dry dramatically differently than the southwest so as they say, individual results may vary.

 

[Norm Marentette]

Tried them all, haven't had the same results as Leo but noticed that bowls with no knots, etc. should be sealed with CA at the very least. I now am sealing knots if any, then using glue and water mix on tenons, then using log sealer from woodchuckers.com (half the price of anchor seal in Canada, let it dry in cool garage at the moment for about 2 weeks, then stack neatly in crawlspace of house, 70 degrees approx. on cement floor for a year. Currently have approx. 150 bowls rough cut, maybe lost 5 bowls so far. Most are hickory and hackberry, which is even more prone to cracking with ring shake. Next lot will be mostly walnut. Already found first walnut bowl so easy to turn and work with compared to Hickory. Sometimes if I really want to slow down drying especially in first week I will cover stack of rough cut bowls with large garden paper bag. Have been roughing all bowls at 10% of dia. also.

 

[hockenbery]

Thank you Al. Does this stability mean I should rough turn larger walnut bowls to < 10% thickness?

There are several variables. Grain orientation, position, how well you recenter the dried bowl, etc

If you rough turn a 20” diameter bowl with center of the bowl on the grain with rim toward the center -
The dried bowl will shrink about 0% in the long grain direction. Most of the perpendicular shrinkage to the long grain will be radial.
So the OD of the 20” bowl will be about 20 x 18 7/8. With a 5.5% radial shrinkage.
To get back to round you cut 9/16 off each endgrain edge and 0 off the side grain edge of the rim
If you want a 1/2” wall you need a wall thickness of 1 1/16. - if everything is perfect…..

you won’t get the bowl perfectly centered on the grain.
You won’t get the bowl perfectly centered to return it
You probably need to take of more wood after the bowl is round to get a sandable tool surface. 1/8? 1/4? Which add 1/4 or 1/2” to the thickness.

2” wall thickness is comfortable. 1 3/8 wall thickness is pretty risky for getting a 1/2” finished wall thickness.

You know your skills at centering blanks on the grain, centering blanks on the lathe, centering dried bowls for returning, cutting to smooth on the second turning.

I wouldn’t recommend a wall thickness less than 1 3/4 at the rim it can be 1 1/4 at the bottom to get 1 3/4 with a 1/2 tenon.
I always want some wiggle room if I haven’t done everything perfectly.

 

[Joe Cincotta]

Recently I've been chainsawing large bowl and platter blanks from black walnut trunk sections (25" total diameter; 20" heartwood). After rough turning and coring, the largest bowl is 20"+. Using the 10 percent guideline, wall thickness is 2" or more. Regardless of using paper bags, sealer or another method to prevent cracking, is there a diameter where you start to lose significantly more stock? I'd rather find out now vs a year or more later. I understand few people want finished bowls anywhere near 20". My intent is to donate them as auction items for nonprofits events, etc. If I'm likely to lose a large percentage of these bowls I'll start with smaller blanks and be content with a diameter that is much less prone to cracking. Thanks in advance for any words of wisdom!

I dry most of my bowl blanks using desiccant beads with no issues. Takes a few days at most, but the are only 6-10". On a side note would you be willing to sell a blank or two? I'm looking to some very large Walnut bowl blanks, I had a few that I turned "22"x 10" that I gave as gifts to family members ands now have other family wanting one as well. I just can't seem to find blanks that big any more.

 

[Rip Littig]

I dry most of my bowl blanks using desiccant beads with no issues. Takes a few days at most, but the are only 6-10". On a side note would you be willing to sell a blank or two? I'm looking to some very large Walnut bowl blanks, I had a few that I turned "22"x 10" that I gave as gifts to family members ands now have other family wanting one as well. I just can't seem to find blanks that big any more.

I wish we lived closer Joe. Considering how large and heavy they are, shipping becomes too cost prohibitive unfortunately.

 

[Don Stephan]

All my bowls are once turned, usually salad mixing bowls 14-20" diameter, wall thickness around 1/2". They are dried in paper bags on a concrete floor on grade. Small cracks are filled with tinted epoxy, seldom have a significant crack that makes the bowl suitable for a hand towel lining and cat bed.