Bowl cracked on lathe overnight

[MarkAndrews]

I've been trying to use free wood for my projects so that I can learn how to prepare blanks, dry the roughed bowls properly etc. I had a bunch of ornamental pear logs (it's quite popular in Southern Calif for lining the streets) The bowl pictured was turned from an approximately 3" thick slab that was near the pith but there was no pith in the slab. I turned the bottom, formed a recess for my spigot jaws and then shut down for the night. When I came in this morning it had cracked as you can see from the pictures.
I'm really curious what I did wrong? The bowl was mounted on a worm screw. Should I have unmounted it and saved it in a bag with shavings overnight?
This was an odd log in that the pith was way off center. The slab was cut from the thicker side of the log, could that have anything to do with it?
Thanks in advance

 

[Mike Johnson]

Freshly cut and turned green wood will dry quickly, you need to wrap it in plastic, or put some anchor seal on it, or put it in a bag with the wood chips that came from the wood turning to slow the drying process down. There are a number of methods used, but you need to control how fast the moisture leaves the bowl blank.

 

[hockenbery]

@Mark Andrews
My guess is the wood dried some and needed to move and could not so it split.

In a while you will be able to rough turn a bowl in under 20 minutes.
For now keep it from drying while you work on it.
If I leave a piece on the lathe to talk on the phone, I wrap it in plastic
If I think it is getting dry I mist it with water from a pump spray bottle.
I live in Florida and we have humidity helping most of the year.
If I would have to leave a piece for along time I would mist it to wet then cover with plastic bags.

You might find some useful information in a thread about working with green wood in the
Tutorials and tips subnforum.

http://www.aawforum.org/community/index.php?threads/working-with-green-wood.11626/

 

[john lucas]

Ditto everything Al said. I put plastic over a piece I'm turning if I stop for anything, lunch, potty break, etc. I've had them crack at the slightest drying. I also use the water mist trick especially on hollow vessels.

 

[Zach LaPerriere]

Great advice. I hope I don't loose you, but here's something to consider with wood movement...a wee bit of theory. If you consider that many people rough a bowl inside and out, then dry the bowl with plastic wrapped on the outside (but not the inside) you start to get an idea why drying on the outside when the inside is solid might be a bad idea. In short, the outside of your bowl dried some, shrunk, and the inside was solid. The fibers were in tension, ie. being pulled apart. Different species have different abilities to withstand this tension.

I see that your bowl was heart down, so that's where the crack started. Had the bowl been heart up, the crack would have started at the top. If you had a time lapse video, my guess would be that the crack started very close to the base, closest to the heart. My guess is that if the bowl was quartersawn with the heart some distance from the actual bowl you would have probably got away with leaving it overnight.

I really like heart down bowls. The grain is often stunning, but drying is a little different challenge than the standard heart-up. And in the usual heart up orientation, if there's a little cracking, you can always make your bowl shorter.

Finally, for what it's worth, I pretty much always hollow the inside right after shaping the outside.

 

[Bill Boehme]

I've been trying to use free wood for my projects so that I can learn how to prepare blanks, dry the roughed bowls properly etc. I had a bunch of ornamental pear logs (it's quite popular in Southern Calif for lining the streets) The bowl pictured was turned from an approximately 3" thick slab that was near the pith but there was no pith in the slab. I turned the bottom, formed a recess for my spigot jaws and then shut down for the night. When I came in this morning it had cracked as you can see from the pictures.
I'm really curious what I did wrong? The bowl was mounted on a worm screw. Should I have unmounted it and saved it in a bag with shavings overnight?
This was an odd log in that the pith was way off center. The slab was cut from the thicker side of the log, could that have anything to do with it?
Thanks in advanceView attachment 22257

The shape of the roughed out bowl has an impact on cracking during the drying process. A shape that is spherical or elliptical has the best chance of surviving the drying process. Your bowl blank has a fairly flat bottom and vertical sides which will be much more likely to crack while drying.

After the bowl has been rough turned, I coat it with Anchorseal and let it dry for several months. Anchorseal is wax and water emulsion that slows down the drying process. The slower that a rough turning dries, the better the chances that it won't crack. Other turners put the rough turning in a paper sack to create a humid environment that retards drying.

 

[john lucas]

I don't use the plastic to dry the bowl just to preserve it for a few hours or even a day so that I can finish things.

 

[Raul McCai]

you might be able to save the bowl with a band saw and glue.
But :
What every one else said: Wrap the green wood in plastic for overnight.
I will toss shavings in to the bowl and wet them down. I'll wrap wet rags or paper towels around a piece and then poly wrap it.

 

[Bill Boehme]

you might be able to save the bowl with a band saw and glue.
But :
What every one else said: Wrap the green wood in plastic for overnight.
I will toss shavings in to the bowl and wet them down. I'll wrap wet rags or paper towels around a piece and then poly wrap it.

Wetting down the shavings or using paper towels to keep the wood wet are both good for times when you need to interrupt the turning overnight. What I have heard others say that they do after rough turning is put the bowl in a paper sack and pack shavings around the bowl. Maybe that might work in a very humid climate, but not around here. In this climate the shavings are nearly dry by the time they hit the floor and if I were to pack them around a rough turned bowl it would be like putting a desiccant in the bag with the bowl ... not a good thing.

 

[Mike Johnson]

I have put some of my freshly turned bowl blanks in plastic grocery bags and tied it closed.
I have also used a damp towel and wrapped the bowl inside the towel.