Green Wood Drying for Other Than Bowls

[LANKFORD]

So far, I have read about drying wood and 99.9 Percent of the info and replies to questions relates to bowls. What about turning green wood or maybe still-a-little-wet like 25-35 percent moisture content for items such as bud or weed vases that are basically a solid item with maybe just a small hole for a weed or flower. What kind of warping, cracking problems might I encounter? And would it be possible to get a finish on something around that 25-30 percent mark? Most of my dry wood is still about 8 to 15 percent moisture content which I guess is what it stabilizes at in Virginia.

 

[Bill Boehme]

It does not really matter what you turn, the warping and cracking problem (actually, more correctly the drying process) is the same whether it is a bowl or something else. Some woods are just about immune to warping and cracking and other will move all over the place and crack like crazy if not properly dried. Things like wall thickness and whether the pith has been removed can greatly affect cracking. Sometimes warping is not a problem, but if it is, let the wood dry after rough turning before doing the final turning.

Bill

 

[Jeff Jilg]

I agree with Bill. If you are trying to keep a piece like an 8" thick piece of wood with the pith in it (like a small log) intact, it will be tough. Even if you dried it under controlled conditions the pith will will not shrink as much as the outer diameter of the piece of wood. This will cause radial cracks in most woods. In this situation there is no way to avoid them, unless you use mesquite. And even mesquite cracks sometimes.

With all wood drying processes, the objective is to dry the whole piece of wood at the same rate. The easiest way to do this is to control the rate of moisture loss and let it dry slowly. The fastest way is with a kiln, where the humidity is controlled, and is slowly reduced at a controlled rate.

Some woods are less prone to cracking. But even the same species can be erratic. I have 3 chinaberry logs in my garage now. They are from 9/05 and each is about 8" dia x 2 feet long. (I originally was going to rough process these by 12/05). Anyhow, 2 have minor cracks and 1 is almost crack free. The wood is probably down to 30%. It is a very porous wood. Sometimes you get lucky. The same situation with oak would have resulted in 3 heavily cracked logs (unusable).

 

[TurningDog]

it also helps to leave whole or split logs as long as possible, especially when you do nothing else to them. Since most of my pieces have natural defects in them anyway I don't get upset about having some cracks in the final piece no one but me knows it was just from storing it. It also helps to store logs off the ground if you store them outside, I usually store my whole logs on top of pieces I am trying to spalt from direct ground contact.

 

[john lucas]

I have been working on things you can make from green wood and it's a difficult topic. You can of course make chair legs, that's been done for years. I have developed a way to make 3 part christmas ornaments out of green limbs. I have been trying to figure out a way to make things like lamps and weed pots out green logs but I'm not sure it can be done without hollowing them in some way or going to the extremes of boiling, alcohol soaking or some other messy expensive system. Controlling the drying of uneven thicknesses is the problem.

 

[TurningDog]

you can of course dry your rough turnings in the microwave if the are small enough and if not in your regular oven set at 100 degrees with the door cracked open with the fan running (my wife hates this method). Or of course find yourself an old fridge and make a kiln out of it. A good place to get those fridges is http://freecycle.org/ also a terrific place to get free wood

another thing that works well for me on boxes is rough turn a 3 to 5 inch cylinder 12 to 18" long and wax the ends. If you make a lot of boxes like i do this a great way to have the prep work done and make for easy storage. once mostly dry I can simply grab a cylinder from the neatly stacked pile part it into 3 or 4 boxes and either rough the boxes then microwave to final or rough then micro dry and finish.

 

[MichaelMouse]

It's Scientific

Until the wood reaches ~30% moisture by weight, not a problem. Not a problem downhill from there unless it's a "difference" problem. Wood will change dimension in predictible and linear fashion as it loses the bound moisture regardless the shape it's in. While we can mitigate the effect of this change, we can't stop it, so we have to plan for it instead.

Though they're a bunch of Packer fans, the folks at the Forest Products Laboratories have done a lot of research, the results of which are posted here, http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm as well as at the main site, if you use the search. Chapter three of the handbook, though you'll want the whole thing, is a pretty good place to start.

Look carefully at the diagrams of dimensional change, and the tables of percentage change, and make good use of the knowledge you gain. For a practical demonstration, look at the construction-grade lumber at the local yard. Look at the orientation of the rings and the direction of change, and soon you'll know without looking at the rings, rather from the shape of a piece, where in the tree it originated. That's the key to predicting direction and dimension change.

Best thing for you to do to begin with is read, second, is to get yourself a hygrometer - humidity gage. That's the key to predictable and safe drying, control of relative humidity. Can't exercise control over an unknown.

 

[Brian Hahn]

So far, I have read about drying wood and 99.9 Percent of the info and replies to questions relates to bowls.

The reason is that there really isn't a way to dry solid objects significantly faster. It takes time for the water to migrate out of the wood, and the thicker the wood the longer it takes. You can speed the process up a little bit, but nothing like the speed-up from rough turning a bowl.

At one time I tried PEG (polyethylene glycol 1000). It eliminated the cracking and checking but had a host of disadvantages, the biggest ones being that the process and subsequent drying take much longer than untreated wood, and that finishing can be a problem.

I've had good luck drying larger billets (up to 5" square) by heavily waxing the ends and coating the sides with shellac (several coats for the large ones) and then letting them air dry for a couple of years. But that doesn't work for all woods (white oak has been a real problem).

As far as finishing a wet piece, penetrating oil finishes (i.e. Danish Oil) seem to work reasonably well. Once the surface is dry, thin film finishes (wipe-on oil, shellac, wax, etc.) will adhere, but the finish must be thin and flexible to allow for the wood movement as the piece continues to dry. Either method of finishing will also retard the moisture loss through the surface and help to reduce cracking, especially if the finish really soaks into the end-grain.

 

[hockenbery]

I turn my hollw forms from green wet wood even wall thickness and just dry them, sand them, and finsih them. The drying I do by putting them in a cardboard box for 1-2 days withthe flaps almost closed. open the flaps for 2 days a day or two on a shelf and they are ready to sand. I do my sandi off the lathe.

For weed pots you can rough turn them, bore a small hole and speed dry them. preheat the oven to 450. TURN the OVEN OFF. put the weedpots in the oven and leave them untill it totaly cools. Remember wood burns so turn the oven off. The weed pots will get a lot of cracks. In most cases the cracks won't be a structual issue for returning. The returned piece will be round and stll have the deep cracks which just add character.
also weed pots turned from Bradford pear limbs 4" diameter often won't crack especailly the ones that break off when snow is predicted since they are dorment.

Lankford: check out the Capital Area Woodurners located in your back yard. They have a bunch of freindly folks, many of whom turn wet wood.


happy turning,
Al

 

[Jim Stoppleworth]

Though they're a bunch of Packer fans, the folks at the Forest Products Laboratories have done a lot of research, the results of which are posted here, http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm

.........and as PACKER fans there is something wrong with them?

Thanks for the URL!

Stoppy
Packer fan for nearly 60 years.

 

[Bill Boehme]

.........and as PACKER fans there is something wrong with them?........

Is that a question or a confirmation?

Bill

 

[Jim Stoppleworth]

It was a ? 😀 MM will probably turn out to be a Viking or Bear fan

 

[Gil Jones]

Weed Vase Turned Green

While I agree that green wood weed vases with a thick, wet, base end are subject to cracking, I have successfully turned them in two secessions (2 days) with no cracks. Make your blank an extra several inches longer, mount between centers, turn a scroll chuck spigot on both ends, and with a parting tool, cut off one end about 2+ inches long, and set aside. Remount the vase in the chuck (this end is the top), and rough turn the lower outside shape, leave the neck thick (I do it with the tailstock support). Back off the tailstock, and bore a hole in the base, leaving about 1/2" of wood around the hole (I use a Forstner bit, and drill in as far as I dare). Then hollow out the base to about 1/4" wall thickness (unless you have a boroscope you will never see inside). Now chuck up the end that you cut off, and turn it to a snug fit into the base hole. Put the vase back on the headstock by the neck spigot (I use two chucks so I do not have to worry about alignment). Now glue the plug into the base using the tailstock for a clamp (I use Gorilla glue as it reacts well in green wood). Try to align the grain correctly and the plug will hide itself. After the glue is cured, reverse the vase in the chuck (base end in the chuck), and finish turning the outside, drill the neck hole down into the hollowed base. Sand and finish. As you are parting off the base plug spigot, and if have room, cut a small groove at the plug line, and one above and below it. Sand and finish the base foot, and the three grooves will effectively hide the plug line. Presto
It takes longer to talk about it than to turn it.

 

[MichaelMouse]

.........and as PACKER fans there is something wrong with them?
Packer fan for nearly 60 years.

Well, of late, they seem a bit too involved with "4" play. Have to look ahead to the main event a bit more.

As to the original, there's a good dance going on around the realities related in the url I referenced, that being that end grain dries at 10 times or more the rate of face grain, with quarter grain even slower than that. Since a vase can be in any shape, you can use this and the direction of contraction to your advantage by bulging the sides a bit more, bringing the end grain into closer contact with the air, as well as denying hold on adjacent fiber over any great length, which will minimize secondary distortion. One end grabs wood and pulls, one only air, and gets pulled in the opposite direction by the end of the wood beyond. Same principle involved in turning thin and allowing warp.

Adding energy to the equation by microwaving or heating from the outside is another way to lower the relative humidity, increasing the rate of drying, but it doesn't alter the fundamentals of distortion unless you physically intervene. I have done a bit of that by taking wood plastic from the microwave and forming it around a split wedged core. Delicate dance between too much wedge and too much shrink, though.