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New here, sorry if this question is answered somewhere. I had trouble with the search engine (sent me to Google). I had a dried bowl (I used the denatured alcohol method) on the lathe and it was really out of round, I had a real hard time trying to get round, it finally broke. I think I had the walls were to thick. Does the thickness of the walls effect how much it goes out of round?
The "rule" is for a rough blank bowl, the wall thickness should be 10% of the bowl's diameter. For example, a 10-inch bowl should have a wall thickness of about an inch. For oak, I have found this to be reasonable. Wood, being what it is, will always throw interesting problems at you in the form of knots, hairline cracks, decay, insect galleries, and "internal stress". These irregularities are what makes your bowl go out-of-round in drying. I use simple air drying in the top of my shop. Depending on the species and initial moisture content, bowls are ready to finish after 4-6 months in L.A. (Lower Alabama, USA). If you turn enough, you will eventually have a catastrophic failure while turning. Start at lower RPM, wear face protection and try to stay out of the "line of fire".
No. A bowl goes out of round based on where and how it's cut from the tree and whether or not is has internal stresses. Read up on wood movement to learn more about where and how to cut the wood from the tree. Internal stresses can be a real trick. A limp that is horizontal to the ground will have a lot of stress and will move more than wood from a vertical trunk section. Don't know why you had a hard time getting it round other than the fact that your just hitting 2 parts of the wood per revolution until it gets round. Most of that is just learning to cut effectively. If you using scrapers then it's just a matter of possibly taking smaller bites per revolution.
Thank you guys. John I am using Easy Wood carbide cutters and have had decent success for the most part. I turned 10 or 12 green oak bowls, the I had trouble with was 4th one the other three worked out fine. There was a small crack that was probably the root of the problem. Richard I know air drying the rough bowls is probably the best way to go, but I am 70 and really new to turning and don’t want to wait that long. I am still a the bottom of the learning curve so I have a ways to go. My goal is to live long enough to get to (or near the top of the curve. :-)). Thanks again for your input.
As John has already pointed out, wood movement is part of where the blank comes from within the tree but I also add that it comes from the type of tree, how much residual moisture is in the blank when you start turning it, as well as what season the wood was harvested. Depending on the size of the blank, and other factors, I'll rough turn my walls to just under an inch or so. To date, that's never been a problem. When I first started turning...there were several times I was very worried that I would actually have enough wood left to 'true' a blank. With respects to drying...I would recommend you do both and see which one works best for you and your style in the long run. Remember...70 is the new 60, you have many miles to go...
When roughing out a bowl, the thickness is important. If roughed too thick, the blank will crack from drying stresses, if roughed too thin, there will not be enough wood to turn it round because of the warping. Some species warp more than others and some blanks warp more than others from the same tree. Oak is a difficult wood for twice turning as the margin between too thick and too thin is small on most blanks and that margin may be non-existent on some pieces. Careful selection of blanks and careful drying makes rough turning oak possible and if you had only one failure from 10 blanks, that is not bad at all.
Thanks John, I will go ahead and put a few in a paper bag on a shelf and compare.
Stevan,
I've had good luck with a paper bag and letting blanks dry until they stop losing weight (a postal scale works-- it's impressive how much water they lose as they dry) before finishing them up. I've also had reasonably decent luck with bowls that are small enough to microwave. Nuke them for a minute or too until they are steamy, let them cool for a few minutes on the counter, and repeat. If I use a microwave, it's on finished bowls (not thick blanks), and while there can be some warpage, it seems to be less than letting the bowls dry on their own. Do note that if you microwave them too long, you can get the bowls to smoke-- so take it easy and don't leave them unattended.
Thought I would try an experiment, for me anyway. I turned and sanded complete a small live edge green oak bowl today. Turned it down to about 3/8”, I went ahead and dropped it in my alcohol bucket for a couple hours. Tomorrow I plan to finish it with some Danish oil. I am curious as to what it does as it dries. I will update.
I turn bowls to 10% wall thickness for every inch of diameter. So roughly 1" thick for 12" bowl. That usually leaves enough wood to get it back to round without making the walls too thin. I coat the end grain areas with Anchorseal and put the bowl in a paper bag. That has worked about the best for me here in Tennessee. The area where I store my bowl blanks has a very high moisture level which really helps slow down the drying process. Slow is the secret. I have dried solid pieces with only the outside turned. Took more than a year to dry but then I was able to turn just a 3" bowl in the middle of a 12" piece. I wanted this piece to have that weight. I never really took the time to play with any of the rush process's. Too much trouble. I just rough turn it and put it on the shelf. If you do this regularly you wlll have a shelf full of dry bowls in 6 months. So I rough turn a piece, take it to the shed, pull a dry one down and then finish turn a piece. No mess, no nasty chemicals around, not expense of propane to boil a piece. Just lost of turning.
Stevan: I follow John Lucas' method. I'm in Ottawa Canada, and we get large temp and humidity swings over the course of a year. Since I'm only turning for fun, I'm in no hurry to get the rough outs dry. That said, I do most of my bowls "once turned". I like the warping and I get instant gratification. I turn then anywhere from 1/8 to 1/4, sand them and let them warp. They dry in no time and I finish sand and oil them. Both methods have their pros and cons, and produce very different end products.
Have fun.
Stevan I do normally make the wall thickness 8% of the bowl diameter, and go slightly to a thinner wall lower on the rough turning, but 10% should give you a bit more leeway, it just takes a little longer to dry.
I do have a lot and longtime experience with turning and drying wet woods (approx 60 years), I tried all the “Too good to be true” drying methods, and have kept on doing and still use what works for me, namely drying in a brown paper bag.
I’m not a production turner and turn for my pleasure, taking the time to do it right.
Stevan, you don’t have to copy someone else, you do have to understand what happens and how you can control it or at least try.
Trying to keep this simple, see Wood as bundles of straws, they will dry in the air, fast or slow depending on how dry the air is and if it is moving, temperature also influences the drying.
All those straws are held together by a substance that is called Lignin, it is pretty tough stuff or else the wood would fall apart, however heating this Lignin will make it a bit less tough and the straws can move some if they have to.
So as these straws dry they get thinner, not really shorter (one tenth of a procent from wet to oven dry) then we have some straws that are different than the rest, the pith area straws have been fed to grow up fast in the length, while the later straws that are more rigid to keep the stem from falling over and these will become the heartwood, and these get filled with products the tree doesn’t need anymore, then there are the sapwood straws that are full of saps to enable the tree to grow, but still without any of the byproducts of the tree.
So you can see that even if we could let all these straws dry evenly, there is the difference of the type of straws that have some shrink more or less than the other straws, and some of the stresses in drying wood stem from this, as said before heating the wood will let some of these stresses become less.
But even at normal room temperature the straws can move albeit much slower than if heated like in boiling water, so giving the wood enough time the stresses will get lower.
Of course we have another problem when we turn wood in side grain direction and with all shorter pieces of wood where the endgrain is exposed to the air, where the end of the wood will dry fast, but the wood farther from the end will not (can not) dry like the wood on the end, and now something has to give, splitting is how the difference in thickness is accommodated .
With a bowl we have this endgrain on two sides of the bowl this wood will dry very fast while the side grain is unable to dry at that speed, so if we now can slow the endgrain from drying any faster than the side grain, we won’t get the stresses from that, we can boil the bowl in water to heat the lignin and enable these straws/wood to move, reducing the stresses.
There still will be some stresses but most wood will be able to accommodate these, here is were the pith wood lets us down, it is different than the heartwood and also weaker and will split very easily, often in minutes after being exposed to the air it will start splitting, keeping the pith out is a good idea.
I have used brown paper bags to slow down the drying of my rough turned bowls, this works if you can keep the drying slow enough, not every place is identical, but most places people live in are very similar, outside or shops and garages etc don’t have to be,
So now we place a wet bowl into a brown paper bag, the brown paper bag with a wet rough turned bowl will get the air in it and that becomes totally saturated with moisture, and so the drying stops, now the paper bag will absorb some of the moisture in the air in the bag, giving the air in the bag to take some more moisture from the wood, air from around the bag will take moisture from the bag, and so the paper bag will absorb some moisture from the air in the bag, and so on and on it goes.
By reducing the speed at which the paper bag dries we will or are able to control the speed of the bowl drying inside the bag, and this is up to you, I have a 99% succes rate or better even with fruit wood like Apple.
For me, I place the bag right on the floor in my basement, where there is no air blowing and no heating from the sun or other, I never add anything to the bag, as this would lay against the wood and prevent the wood from drying, making the grow of mold/fungus very likely, even anchor or wax seal get often enough mold under it, mold is something I still will check for in the first week or two, if there is any, I just wipe the bowl dry and place the bowl in a dry bag, and close the paper bag again, the wet bag can be used again when dry.
Here the rough-outs in the paper bags, and then later I let them dry out of the bag some more, making and drying more bowls than selling them gets you spares, problem is you need room to store them, I kept running out of room
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As we moved to a new place here, I brought all of my bowls along (Actually too heavy for my trailer, but we got here) I got more room for my bowls, counted them when loading and unloading (approx. 1000 bowls) storing the larger bowls overhead in my shop, and the smaller ones in a storage unit.
You won’t find split bowls, they do not split from drying if done right, (SLOWLY) in a brown paper bag, with nothing else added or done to them.
I guess it is just too simple, or maybe too slow for some, mother nature will win every time.
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Leo that is the best explanation of drying wood I have seen for a while maybe ever.
Thank you Fred :), now if people would only read it, and follow the suggestions, they would have better results drying their bowls, boxes and hollow forms :DQuote:
Originally Posted by Fred Belknap