Sealing Turning Blanks

[Barry McFadden]

Usually when I get some tree trunk logs to turn I slice about 2" out of the center to remove the pith then seal it for later use. I usually seal both ends and the cut facegrain part. My question is...should I seal the facegrain or leave it so the moisture can escape to dry the piece quicker. Just wondering what other turners do....

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[Prashun Patel]

I seal the whole thing. I prefer to rough turn the blank before leaving to dry, but YMMV.

[Barry McFadden]

Thanks Prashun.....

[John Keeton]

I would seal just the end grain as trapping the moisture can cause degradation in the wood. It needs to dry, but just slowly. Like Prashun, I would prefer to rough turn it and then seal the outside only, but include the rim.

The blank you show has too much of the center pith area for my tastes. My guess is it will be prone to crack in the center.

[Neil Strong]

I seal the whole thing. I prefer to rough turn the blank before leaving to dry, but YMMV.

I also rough turn blanks before leaving to season.

My preference is to put them in plastic bags (that's quicker and easier to do than paint) and get them rough turned before they spalt.

If I get too many at once and know I won't get through the rough turning quickly enough I will paint the ends and some of the top face as a temporary measure...


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PS - for scale, see axe in first photo

[John K Jordan]

Usually when I get some tree trunk logs to turn I slice about 2" out of the center to remove the pith then seal it for later use. I usually seal both ends and the cut facegrain part. My question is...should I seal the facegrain or leave it so the moisture can escape to dry the piece quicker. Just wondering what other turners do....

485729

Dry indoors in Heat/AC, or outdoors?
High or low humidity?
Hot summer or frozen winter?
What kind of wood?

In general you want to dry slowly to reduce the chance of cracking. Also in general, moisture escapes from the end grain much quicker than in other directions. The wood will develop a moisture gradient from the inside out. The more equal the gradient is throughout the wood the smaller the stresses that cause cracks. If drying a thick chunk of wood quickly, the outside surfaces may soon be much dryer than the inside and the high shrinkage can cause cracking. Better to dry slowly. Look sometime at a schedule for kiln drying. Depending on the species the temperature and humidity in the kiln have to be controlled carefully or the wood can dry too fast and much of the kiln load may be worthless.

If high humidity I generally just seal the end grain, even if it pretty warm. However, wet wood in higher temperatures can degrade rapidly. Some species like maple or holly might discolor quickly, especially in the summer. In the "right" conditions fungi may cause beautiful spalting.

In lower humidity, I also seal the faces, depending.
By face grain, if it's the top surface in your picture, that is a radial section. A cut in the radial direction is relatively stable compared to a cut in the transverse direction.
If you were to cut off a slice on the other side, the side that's down in your picture, if you don't cut extremely deep you will expose a transverse direction. As wood dries the amount of shrinkage in the transverse direction is about twice that in the radial direction so the chance of cracks/splits on that face is much higher. In that case, I will also seal the transverse face. Note that if you DON'T cut a slice off the bark side the moisture will still escape through the bark, more in some species than others. The bark can act sort of like a sealant. However, left long enough, many species will crack right through the bark. For example, I've seen small log sections of dogwood split down the side and open a wide crack. By removing the pith the chance of cracks is decreased but not eliminated.

I also seal any face that has wild figure such as a crotch or burl.
I also seal any face in SOME species that exposes both heartwood and sapwood. For example, dogwood or privit will often crack along the junction of heartwood and sapwood since the shrinkage is different between them. Many other species are much more stable. For example, it's hard to get sassafras to crack regardless of what you do!

I only seal with Anchorseal. I like a thick coat for slower drying so I pour some into a plastic coffee can and let some of the moisture evaporate leaving a thicker wax emulsion. Note that moisture will go through wax so even if you seal all the way around a blank it will dry. In fact, the more you seal, the slower the moisture moves from the inside to the outside, the less stress is developed by the shrinkage, and the better the chance of the blank surviving. If you ever buy exotic woods, perhaps olive or ebony, the blank is most likely dipped in hot paraffin.

If you do want to keep wood for a long time you can do something called "ponding", submerging the wood, regardless of the shape, in water. Some have used a 55-gal drum. Change the water occasionally to keep it from festering. The wood will never dry out and last indefinitely without cracking. Another thing you can do if you have a big enough freezer or it's cold enough outside is freeze the wet wood.

All that said, you are best off to turn any large tree sections as soon as possible. While certain short log sections are possible to dry, many are not and will eventually crack. I've heard expert advice to never accumulate more green blanks than you can rough turn in a few weeks. The other John Jordan, the famous turner, said that if possible he gets his wood in the entire log and keep it off the ground out of direct sun. A long log will dry the slowly since there is relatively little end grain so it is less likely to crack. When he is ready to turn something he cuts off about 6" and throws it away then cuts of a chunk and turns it right away.

I personally prefer to turn dry wood. I've cut and dried many hundreds of turning blanks over the years and almost all have survived. Most are 3 to 6" squares or rectangles but some have been as large as 10x10x15". As mentioned above, whether I seal just the end grain or some or all of the wood depends. Also as mentioned, the species can make a big difference. If preparing bowl blanks I will cut a fat slice out of the log, cut it round on the bandsaw, then seal it all over and put it on a wire shelf to dry indoors. I record the weight of the blank every few months; when it quits changing it's dry. A large blank may take years to dry.

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Funny thing, the more one learns about wood and how it behaves as it dries the more sense all this makes. I recommend the book "Understanding Wood" by R. Bruce Hoadley. Hoadley is both a wood technologist and a craftsman so his perspective is closer to ours than some authors. He explains things well.

JKJ

[Neil Strong]

Like Prashun, I would prefer to rough turn it and then seal the outside only, but include the rim.

The blank you show has too much of the center pith area for my tastes. My guess is it will be prone to crack in the center.

I don't seal the rough turned bowls, but if I were to do so I would also do it on the outside only ... the cracking in rough turned bowls starts on the outside. As I visualise it, if not slowed down with some form of sealing, the greater outside surface area shrinks with drying and then can't stretch over the inner slower-to-dry internal surface. But, if the inner surface dries first it just contracts on itself and then allows the greater outer surface to shrink onto that smaller diameter with less chance of splitting.

On removing the pith, I don't bother with the woods I mostly turn. What is more important in my experience is ripping the log along the pith line ASAP and ideally as the tree comes down and bucked into billets. Cracks forming from the pith outwards start to happen immediately the log ends are exposed to air, even if you can't see them they are there. Ripping the billet in half along the pith line immediately relieves the radial tension in the log and reduces the formation and propagation of cracks from the pith area. Miss this very short time window and the micro-cracks will already be formed and a margin of pith area will have to be subsequently removed to prevent the the micro-cracks from growing and propagating through the blank.

I have my own method of seasoning the rough turned blanks, which I won't go into here, other than to say I work on a Return on Effort principle in which I deploy the least effort but with an expect loss of about 10-15%, which then become firewood.

I can understand that would be an unacceptable % loss for some turners in some circumstances, but for me the time I save by accepting that % loss becomes productive turning time and more bowls that will go to the gallery for sale.

If I was running out of rough turned blanks I might change my approach, but on my current inventory I reckon I have twenty years of rough turned blanks waiting for final turning, with some pre-turned over 30 yrs ago, but with little prospect of me lasting that long at the lathe...:rolleyes:

[Barry McFadden]

Thanks guys for all the information... I don't like turning wet wood because of all the cleanup of wet sawdust and shavings to prevent rust on the tools so I don't rough turn them. John in answer to your questions..
Dry indoors in Heat/AC, or outdoors?
High or low humidity?
Hot summer or frozen winter?
What kind of wood?
Actually it's all of the above..hot summers, cold winters, humidity swings, sometimes store them in the garage and sometimes in the basement. My wood is mostly Birch and Maple and Cherry that I'm allowed to get from a Provincial Park near here when they cut trees down.

Thanks again for the responses, they have been helpful..

[Prashun Patel]

I also just now took a closer look @ the blank and I too would slab off an inch to remove the pith. To make myself feel better about losing that wood, I quarter saw it and make coasters or little cheese trays. I do those green. Fun to hand plane. I leave them unfinished.

[Reed Gray]

For slabs, it depends on how long until I am 'planning' to turn it. If it is going to be a day or three, I will use the stretch film around the outside. Note here, with high sugar content woods like maple, it can mold under the plastic. Other than that, if I am going to seal the wood, I will use titebond glue. I do prefer to keep my logs whole till I want to turn them, then slice off as much as I will go through. I do prefer to green turn to final thickness and let them dry and warp. The whole thing about drying wood blanks is that every wood seems to have different requirements for getting through without cracking. Had some American Yellowwood once, and it shattered. Found out that is typical for that wood. Some woods are very stable and dry with little trouble. Pacific madrone is my favorite wood to turn, and there is no rhyme or reason to how it warps. I have found that I get less cracking with early spring cut trees than with mid to late summer harvested trees. Just because I guess... Drying is an art.

robo hippy

[Barry McFadden]

I also just now took a closer look @ the blank and I too would slab off an inch to remove the pith. To make myself feel better about losing that wood, I quarter saw it and make coasters or little cheese trays. I do those green. Fun to hand plane. I leave them unfinished.

I already cut a 1.5" slab out of the centerof the log and figured that was enough not wanting to loose too much depth in the turning blank. I'll watch how the pieces progress 9i have about 10 recent ones) and slice off more if they start to crack too much.

[John Keeton]

Barry, if they "start to crack" it is too late as the cracks go much further than is visible. I know folks like to maximize the vessel size from any given piece of wood, but I prefer to remove 2.5 - 3" of material in the pith - half to each side. Just my thoughts - others may feel differently.

[Kevin Jenness]

I don't like turning wet wood because of all the cleanup of wet sawdust and shavings to prevent rust on the tools so I don't rough turn them.

Drying thick unturned blanks is very slow and more subject to degrade than drying rough-turned pieces. If you continue to go that route I would advise leaving extra length on the ends to allow for the inevitable checking, even with end sealing.

Turning green wood is messy but it is a lot easier to shape than dry wood.

[Neil Strong]

if they "start to crack" it is too late as the cracks go much further than is visible.

And, once a micro-crack has formed, even if it's not readily visible to begin with, it is there for good... it will never heal like it might in a living tree.

This is why I always ask when offered a tree, when will it come down? Most only think to offer it after it has come down!

I'm only interested if I can be there when it comes down. If the faller does the cutting while I'm there and will cut the billet lengths to my requirements (11/2 x D) I can rip them down the pith line and bag or seal them immediately. This greatly minimises the formation of the micro-cracks.

There are some trees that develop the cracks down the pith line so quickly that as the faller works their way down the standing trunk (that is the way trees are felled in my peri-urban area, not dropped and then cut into lengths) that you can literally hear the cracks forming in some species as they run down inside the tree trunk, that is if the chainsaw noise stops for a bit to allow you to hear that.

I haven't climbed trees for many years now, so won't tackle standing trees by myself anymore, but I can manage recent windfall trees by myself. A windfall that still has some of its roots in the ground and canopy intact can also wait a bit before needing to be processed, so the timing of the phone call from the donor isn't so critical with those.

[Barry McFadden]

Thanks John,Kevin,and Neil....I appreciate the help...I guess it's better to have a smaller bowl with no cracks as opposed to a larger one that may have too many cracks to make it usable,,,