Finish on Wet Turning

I turned a bowl two days ago out of Silver Maple. I immediately soaked the bowl in denatured alcohol for a couple of hours and then let air dry for a couple of hours. Then into the microwave for a few 2 minute blasts over a half hour period. Then I went out and put on 50% thinned deft. I slathered it on and boy did the warm wood soak up the deft. Especially the end grain. That dried over night. Finished sanded it, sanded the inside smooth, wood burned some lighthouses on the outside and buffed it. Then another slathered coat of deft.

There has been no cracks develop yet. It has begun to warp slightly.

We will see.

I went ot a speaker who discussed the alcohol treatment. He said taping brown paper bags on the outside of a bowl would force the bowl to dry from the inside out would cause the stresses to hold the cracks together. I thought that sealing just the outside with lacquer would do the same thing.

We'll see.

I set aside, too. Sandpaper fine enough to make me happy about the surface clogs with wet dust, otherwise.

Since oil and water don't mix, and water-based won't dry until the water's gone, doesn't make a lot of difference if it dries with or without a finishing agent applied, and sands easier if it's dry.

You can heat to semi-dry, then run oil into the piece and sand it on the lathe, making a mess of everything, but the oil will be gummy until the piece dries anyway.

Absolutely. John Jordan, a turner of some note, does this all the time. Do a Google search on him and see if you can find any details that might help you. He does have a video available on turning hollow vessels. It will answer your questions..

I turn a lot of wet Aspen. What works well for me is to microwave it dry. Most of the time I rough it to about 1/2 - 3/4" thickness then several trips through the micro. Turn the power down to defrost or low and put it in about 3-4 minutes. You just want it fairly warm, not too hot to hold. Remove it and allow to cool on a rack so the moisture can escape all around the piece. Back in the micro when it is cool to the touch. Don't leave it overnight, or it will dry conventionally and crack. You have to keep going once you start. Repeat the cycle 4 or 5 times. You will feel it is done when you remove it warm and don't feel moisture still coming out. Then finish turn and apply whatever finish you want.

Sometimes I will turn to the final sizes before microwaving, but it is hard to sand wet wood and it will warp, sometimes quiet interesting, as it dries.

I've used the micro do dry Aspen, Cottonwood, Elm, Mesquite and Pine all with excellent results, I think I've had 2 pieces crack out of about 100 that did not.

If SWMBO is not keen on your using the kitchen micro, go to any of the big box places and buy a new micro. Mine was $29. It also works well to reheat my coffee that goes cold when I am busy (forget). Warm the Carnuba wax a few seconds and it is much easier to apply to a piece or a buff.

Now as to finishing wet on the lathe? Anything I've tried either dulls, clouds, or both. Sometimes I use BLO and slather it on. It does keep the piece from cracking, but you won't get a gloss finish. After a few days of drying, with some warpage, you can hand sand and try buffing. It does make a nice feeling piece.

If you turn it thin enough you can dry it by sanding, then finish however. When I've tried this I have not been able to get the base dry and get cracking.

Why the rush? If you force the timber to do something it doesn't want to do naturally it will get it's own back on you eventually. A very well known turner's work is now doing exactly that - reacting to a drying process done over 15 years ago.

when I turn something thin, I usually just spray with lacquer and am done with it - no problems. by thin, I mean 1/8 inch or less. At that thickness, there is generally almost no moisture of note in the wood by the time you are ready to finish.

Final sanding and finishing is possible on wet wood, but it isn't easy. When I do this it is usually on burl pieces where I expedct a LOT of movement as it drys, and sanding will be implssible after it is dry. If your cutting and tool work is fine enough, you can start sanding at 180 or 220 grit. When the paper loads up, the rubber cleaning sticks will remove the build up. The only problem is that you have to clean your sandpaper more that you do when you are sanding dry wood. I will put on as much finish as the wood will take in, and wet sand each application in. When done, I use the air hose to blow off any remaining residue especially in any voids. This helps reduce the amount of bleed out that happens with oil finishes. I use Deftoil with urethane resins. This finish never builds up any kind of gloss, probably because of the water in the wood, but it does help keep the wood from drying out too quickly. After the wood is totally dry, and has finished moving, more finish can be applied to get a surface finish. To buff it out, I take one of the synthetic steel wool pads, and cut a circle out that fits my angle drill. It will stay on quite well at lower speeds (hook and loop pad), and at higher speeds as long as you have some pressure on it.

With utility bowls, I do turn to finish thickness, and let them dry. After they are done moving, I then sand and finish them. I wouldn't want to have to sand them without the power sanders. I love the warped and eccentric shapes, because they look more normal to me.

As far as drying I am still experimenting. I have used the alcohol bath, LDD, and plain old air drying. I am starting to think that I will end up going back to air drying. I don't really notice any advantage to either of the bath methods, except that the LDD bowls do tend to sand much easier. Success rate is the same for all methods. This could be because of 2 things. One is that it is rather humid here and when put on a wire shelf in my shop they dry at a nice slow rate. The other is that I turn to finish thickness, rather that leave them thick, and then return to final thickness. The thicker pieces will have more stress, and problems releasing the stress. This is still an experiment in progress, and I am still working on it. robo hippy

Mark, Who is this "very well known turner" and what work are you referring to?

TomNie

Results are similar because it's still loss of bound water, not anything done before it, that counts. We older folks who went through PEG and braces across the center of bowls, for example, did get different results at least. PEG was a clammy mess, and probably 25% of the braced bowls split.

As you've discovered, thinner deforms less than thicker, though not, perhaps, as significantly as some think, because all shrinkage is local, and there's less to grab onto on either side because of the curved shape of the piece.

Try consulting the radial shrinkage table (or tangential for platters) on the FPL site or Hoadley, and using it to determine how thin you can turn and still come back to circularity at the desired wall thickness. If you're impatient to dry, cut close to the minimum needed. Or add a bit more in thickness to allow some changes if the shape you roughed isn't precisely the one you want.

I've got a short stack of ~10" cherry bowls drying now that were roughed at ~3/4, and should give me 1/4 walls plus a bit of redesign room.

George, Until your comments above, if you had asked me, I would have said that thinner pieces will move a lot more than thicker pieces. I have noticed with burl pieces in particular, that when cutting slabs on the bandsaw, the thin scrap on the last piece cut will have much more distortion that the thicker slabs. When turning bowls, the thinner ones seem to have much more distortion. I core all bowls, and the thinnest one of the set will move the most. With straight grained woods, the amount of movement seems to be similar. Madrone seems to be most likely to do this. When cutting dried stock for furniture pieces, the thicker pieces seem to have more binding and spring than flatter boards. I have always wondered if this was because of poor drying and/or unusual grain, and/or unrelieved stresses already in the tree.

Smaller bowls (cored) mean tighter radius annual rings. The thickness, though less in absolute dimension, is also greater in proportion to the circumference, so your observation is pretty well on track. Bowls closer to the core are also more likely to feature irregular grain patterns from failed branches and such, thus increasing directional unpredictability. This is what gets your thin burl pieces moving in seemingly paradoxical directions sometimes. They've been held in equilibrium against the part you removed, and seek a new one. They have grown in a cylinder, and you have created a board, so there will be some stress to relieve.

With bowls the slope of the sides is a major determinant of direction and magnitude of shrinkage. The more vertical the sides, normally the broader the bottom, which means that the direction with the larger proportion of shrinkage, tangential, comes to dominate the radial.

Take a look at

figure 3-3, and mentally make your bowl cuts. Remember, however, that you've taken the middle out of those boards, so as they contract, they pull less on their fellows, and more on air. Among other things, that's why bowls don't split inside out. The inside is in constant compression by drying forces while the outside is in tension, and prone to open. The slope from rim to bottom also determines why the _average_ radial shrinkage is rarely exceeded as the piece dries, much less the tangential. Look at that board center top in the figure, and compare it to your dried bowl blanks. The rim is higher inside the bowl, and the shorter radius annual rings seem elevated above the whole by the shrinkage downward into air. You predict a lot about drying stress by looking at a stud grade 2x4 with the heart close off one surface and see how much it crowns versus one which is farther from center, with larger radius annual rings. Often the short radius stuff will experience drying stress in excess of binding force, and split. Move the heart from the center of the total width for the worst of all worlds.

snip

Perhaps the "growth rings as rubber bands" analogy may help convey the concept. Frank Klausz, a very skilled and experienced furniture maker and the fastest hand cut dovetails person on the planet, uses it to orient the grain of dovetailed drawer sides.

As you can see, the newer growth rings towards the outside of the tree are "stretched" (in tension) more than the ones towards the inside of the tree. As they dry they want to "unstretch". That requires that they get shorter. The only way for them to do that is if the length they're stretched gets shorter. But if the "outside" of the board gets shorter, the inside has to get longer. Because the "inside rubber bands" aren't "stretched" much they don't resist the inside gettng longer much. The result is cupping, with the concaving occuring on the "outside" face of the board. Now with a bowl or hollow vessel, when the "concaving" gets too large something has to give. Either the piece implodes or explodes, the latter manifested as either one big crack or several smaller ones.

Now with flat boards used in furniture making, you always allow for likely expansion and contraction by choosing joinery that will accomodate it and stock selection. Quarter sawn boards are more stabile and are selected for wide or thick parts.

Wood will move. In furniture making you can accomodate it. With turned "hollow forms" accomodating movement seems a lot trickier. Maybe that's one of the logical reasons for making segmented pieces.

Still don't understand why bowls. hollow cylinders or "vases" are so attractive to wood turners. It seems like spitting in the wind - to me. Granted, they can be beautiful to look at, and feel But there's a longevity issue. Will any of today's pieces show up on some future Antiques Road Show like two and three hundred year old furniture pieces do - quite regular- ly? Perhaps some "functional art" should, by its nature, be transient - like a sunset.

charlie b