wooden bowls

[simons360]

l ordered a 4x4x8 block of ambrosia maple and when l finished my bowl and brought it into the house it warped, thought it was dry because it was wax coated. Any help would be a blessing.

[Nick]

Please read what I had to say about "shop drying" in http://www.shopsmith.net/forums/showthread.htm?t=454, then consider this:

The wax coating on exotic bowl blanks is not there to keep the stock dry. It's there to prevent rapid expansion and contraction from changes in relative humidity that might cause the blank to warp, split, or check. If the blank where shipped from one part of the world to another without the wax coating, it's possible that the relative humidity to which it's exposed would shift drastically in just a few days. As it rapidly released or absorbed moisture, the outside of the blank would begin to shrink or swell before the inside and the blank would tear itself apart.

In this case, the wax serves one of the same purposes as a wood finish -- it prevents the rapid release and absorption of moisture, slows down the expansion and contraction, and allows the wood time to acclimate itself to changes in RH. Wax is impermeable to moisture, but the coat is thin enough and there are enough scrapes and scratches in it by the time it gets to you that it becomes, in effect, a semi-permeable membrane that simply slows down the movement of moisture rather than preventing it completely. The blank will still "shop dry," but you have to give it enough time.

One of the things you can do to hasten the shop drying -- safely -- is to scrape the wax off the areas showing flat grain, but leave the coating on the end grain. End grain releases and absorbs moisture much faster than flat grain. The wood will acclimate itself to the RH in your shop, but not so quickly as the resulting shrinking or swelling will cause the blank to check or warp.

With all good wishes,

[charlese]

l ordered a 4x4x8 block of ambrosia maple and when l finished my bowl and brought it into the house it warped, thought it was dry because it was wax coated. Any help would be a blessing.

Last November, I ordered two salt and pepper grinder kits from a vendor recommended by WOOD Magazine. The salt grinders were to be made from maple and the Pepper grinders from walnut. (Thought this sounded like a couple of good Christmas gifts.) The maple blocks were dry, but the walnut blocks pegged my moisture meter at 20% +

Result: The families got their salt grinders with a promise that pepper grinders would be comming as soon as the wood dried out to allow turning. Made 2 plus inches cylinders out of walnut. Coated them with white glue and set them aside to dry out. We live in the Mojave desert and didn't want the blanks to dry too soon. Left them in the unheated shop this winter, since February (miosture was down to 18% near the ends) have taken them outside in the sun during the days. Have even put them in paper sacks and laid them outside in temps of over 90 with humidities in the teens. Today I measured the moisture again. (the meter measures 1/2" deep) They are both finally down to 8% near the ends and 15% through the middles of the blanks. They are getting close! Folks are waiting!

Moral: Drying takes a long time!
2nd Moral: If you can, get your hands on a moisture meter. (Mine is the kind that has no pins)

[james.miller]

Just how much did it warp? Most wood will release stresses as you turn it which can cause it to warp slightly even when it's properly dry. The thinner the wall thickness the more it can warp (the guy that turnes cowboy hats turns them down to less that 1/16" thick). Even some of the stable woods like Mesquite can warp slightly.

If it warped a lot it probably wasn't dry enough. If it's too wet it's probably best to rough turn it to about an inch thick then seal it with wax or put it in a brown paper bag wrapped with newspaper and let it finish drying for several weeks to several months (depends on your RH) then finish turning it. Sometimes the rough turned bowls crack when drying but a lot of the professional turners still rough turn the blanks while there wet.

Some turners intentionally turn thin walled bowls when they are wet so that they will warp, hoping that they will warp into an interesting shape.

I've had some success drying rough turned bowls in the microwave oven. It smells bad and can start a fire if you try to go to fast. If you have a very sensitive scale you can weigh it first. Then put the rough turned bowl in the microwave for 10 seconds. Wait for several seconds then feel how warm it is, if it's just warm nuke it for another 10 seconds. Never let it get hot as you will burn the wood or start a fire. Weigh it periodically to see if it is loosing weight. Keep nuking it for 10 seconds then waiting until it is just warm then do it again. It is done when you don't loose any more weight after a couple of cycles. If you don't have a scale it's done when it doesn't get very warm after a few cycles.

Jim in Tucson

[Greenvilleguy]

I always rough turn a bowl first and then let in shop dry. The concept is that it will warp from drying or just from stock removal stressing the wood differently. If you rough turn first, there will still be enough stock to true the bowl back after warping.

The question always is "How long do I leave it drying?" and the short answer is "Long enough". Purchased wood should be realitively dry and should need only a day or two for the wood to stablize in it's new shape.

With wet wood, I've had some success (and some failures) placing the rough turned bowl in a paper bags or wrapping with newspaper to slow the drying process. Theorically, you should weight it periodically and use it when the weight stops dropping. To be honest, I've never had the patience to do that. I typically wait a month and put it back on the lathe. The good thing about wet wood is that it is free so who cares if you screw up a piece now and then .

I've never tried the microwave approach above, but it sounds reasonable. I've got some wet Bradford pear downstairs. Maybe I'll give it a try.

By the way, I have some wet sweet gum. I've rough turned two bowls. The rough bowls looked great, but the next day they were both cracked. Any ideas on how I can slow the drying process down enough to prevent this? By the way, blanks cut and shop dryed before turning also crack. The squirrelly grain seems prone to cracking, but it's a very interesting wood with lots of grain and color variation.

[simons360]

Rough turning and then l will put it into a bag and keep it in my walk in cooler for a while, think that will work. thanks.

[rcartmetal]

Another approach is to boil the rough turned bowl in water for a bit. This seems to soften the cell walls and allow them to come to equalibrium with one another.

[charlese]

Another approach is to boil the rough turned bowl in water for a bit. This seems to soften the cell walls and allow them to come to equalibrium with one another.

This is very interesting! In the youngsters' vernacular - Radical! Does this really work, Spike? Have you ever tried to change the shape, by clamping or molding, after boiling?

[rcartmetal]

This is an approach that I read about numerous times, and just day before yesterday an old local turner told me I had better do this with the cherry stump I'm cutting up for bowl blanks. He said myrtle needed it too, and as I have recently turned a myrtle bowl from stock that I thought was seasoned and subsequently cracked, I am inclined to believe him. I will do this with my next cherry bowl and report on the outcome.

[Greenvilleguy]

Yes Spike -- please let us know. I'm thinking along with Chuck, i.e. if this works we can intentionally wrap bowls as well creating some very interesting affects.