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George Hankins

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Trying hard to figure out drying bowls without checking / cracking. tried wicrowave, and built a kiln in old oven with 75 watt bulb but still have issues . I dont have enough turning stock to wait 6 months in grocery bag. I own 50 acres of hardwoods in virginia so i have lots of green wood.
 
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Trying hard to figure out drying bowls without checking / cracking. tried wicrowave, and built a kiln in old oven with 75 watt bulb but still have issues . I dont have enough turning stock to wait 6 months in grocery bag. I own 50 acres of hardwoods in virginia so i have lots of green wood.

George,
If you do a forum search on drying, you’ll end up with many hundreds (1000?) of responses to this very question. Unfortunately, your less than 6 month time constraint is really working against you — slow & controlled drying is the key. Patience, Grasshopper.

Just about everyone needs to experiment and come up with what works for the woods they use and their building environment. I turn to about 10% of diameter wall thickness; coat the entire bowl in Anchorseal; place in a cool “pantry” room in my basement; forget about it for a year or five. Some woods are boiled for an hour or more (fruit woods and white oak) before Anchorseal-ing. Then again, I’m in NW Oregon living in a c1920 home with a heating system laid out in the 1960s. This works for me but it took a lot of experimenting to build my knowledge and hit on the right combination for a given wood.

Maybe try combining the “kiln" and paper bag; maybe 40W would be more successful. 25W? Also, I predict your oven/kiln won’t be big enough! (Meaning that given a bit of time, you’re going to have more rough outs than you can manage in the oven, so will end up not getting back to dried pieces for a year or five regardless of your patience level.) ;)
 
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hockenbery

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George,
Like Owen said you need to find what works for you. There are plenty of Woodturner's in Virginia successfully drying bowls.

to avoid cracks the Wood needs to be able to move as it dries.
Roughed out bowls with an even wall thickness of about 10% of the diameter and flowing curves will dry without cracking most of the time.

You might try a Soft maple ( if you have access to red or silver maple). It is a more foregiving wood than most.

My suggestion is to turn 3 bowls most turning days.
A natural edge with a wall thickness of 3/16". this will dry in a few days
Two 10" diameter bowls with a wall thickness of 10" Dry one in the microwave and dry one in paper bags for 6-8 months. You will have the natural edge bowl and the microwaved bowl ready to finish in a few days. An in 8 months you will have established a pipeline of dries bowls.

Microwave - I rub bee's wax over the endgrain of the bowl inside and out.
Microwave the bowl at 40% power for 3 minutes let the bowl cool for 10 minutes and repeat until dry. 8 to 10 cycles is usually enough. If the bowl is really hot to the touch triple the cooling time. When moisture stops coming out of the bowl is dry.

ALWAYS WATCH THE MICROWAVING WOOD CAN CATCH FIRE IN A MICROWAVE.

Slides I used in a "working with green wood" demo may give you some useful tips.
http://aaw.hockenbery.net/WORKING WITH green wood-HOcompressed.pdf
 
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Hi George,

Great advice so far. I don't know much about boiling, but that's an established way to dry quicker...worth a search here, lots of good info.

The other distant possibility is to search your forest for a suitable species that may be either standing dead or blown over. The caveat: lots of species are already rotten, check, or otherwise unsuitable when they are dead. That said, a few species are unbelievably dry when standing dead and still sound wood.

I don't know the first thing about Virginia wood, but some species will also dry very quickly and stay together. Mountain ash (aka Rowan) is one suitable species here in the rainforest of Alaska...you can pretty much get away with taking a green rough turned bowl and bring it into a house measuring as low as 30-35% RH and have the wood dry in a week with no checking.

Option #3...talk to some local turners for some dry blank in trade for green wood.
 
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Other options include turning purchased dry blanks while your 'free' wood is drying or buy some already dry rough turned blanks (roughoutbowls.com--I have no financial interest). You might also make a plea to other members of your local turning club, asking for donations or even a loan that you'll pay back when all those green logs have finally become dry blanks.
 

Bill Boehme

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Welcome to the AAW forum, George.

What works for me is rough turning, coating with Anchorseal, and let dry in my air conditioned garage about three months for small bowls (8" diameter) and up to six months for really large bowls (18" diameter). In my climate the idea is to slow down the rate of drying. Accelerated drying runs the risk of various problems. Really the wait isn't a problem once you get your production stream filled. The initial delay in finished product shouldn't be too much of a problem if you are able to keep busy roughing out bowls.

Something to consider is how you are roughing out bowls. The profile and thickness can both affect your success rate. For example, if you are turning face grain bowls (grain direction is perpendicular to the rotation axis), the bowls with a cross section profile that has a circular arc from rim to bottom or something similar such as an elliptical or parabolic curve from rim to bottom are much more likely to dry without cracking than one with a somewhat square cross section (flat bottom and vertical sides). Thickness of the roughout also has an effect on the outcome. If it is too thin then the amount of warping during drying will not allow you to do a final turning. If it is too thick the drying will be slow and there will be an increased risk of cracking. The generally accepted rule of thumb is to make the rough turning wall thickness about 10% of the diameter.

A couple final thoughts about rough turning is that the thickness should be uniform from rim to bottom. If the rim is thin and the bottom is thick then there is a high probability of cracking. Finally, don't include the pith in any of your bowls because it will be the source of cracking.

If you have any pictures of problem pieces, that would help us diagnose any problems that you are having.

Here is an example of an eyeball parabolic curve which is precise enough for most purposes.

image.jpeg
 
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Thanks for all your advice. I do have several hundred board feet of dry walnut boards that i cut with my dad 35 years ago but glued pieces just dont pop like natural pieces. May try the boiling method and see how that works?
 

hockenbery

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@George Hankins
Hooking up with a local chapter of AAW will connect you with successful turners who can point you in the right direction. Maybe get some mentoring.

Keep turning! As you get more experience fewer and fewer of your bowls will crack.

The keys to success with green wood are: keeping the wood from cracking before you turn it, aligning the grain in the blank, working fast enough to keep it from drying while you turn it, turning curves, turning even wall thickness, controlling the drying.
Each of these require experience to master.

new turners rarely turn a shape and wall thickness that leads to successful drying all of the time. Experienced turners get the shape and wall thickness all of the time.

A hemispherical shaped bowl with even wall thickness will dry successfully most of the time.
Bowls with flat bottoms and vertical walls are extremely difficult to dry successfully.

Have fun
Al
 
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George,

I second the advice to get together with your local turners. I turned for a couple of years on my own since I live in a small town, and my learning curve was much slower. Even with plenty of previous woodworking experience. Turning is just different.

Idea #2: start turning some platters with your walnut boards while your rough bowls dry. Platters aren't as immediately satisfying when we have the bowl bug, but I've grown to love turning them too. People get so excited over platters and plates. And there's nothing like eating off of a wood plate. You really don't need more than an inch of wood to make some great stuff.

Happy turning.
 

odie

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George,

I second the advice to get together with your local turners. I turned for a couple of years on my own since I live in a small town, and my learning curve was much slower. Even with plenty of previous woodworking experience. Turning is just different.

Idea #2: start turning some platters with your walnut boards while your rough bowls dry. Platters aren't as immediately satisfying when we have the bowl bug, but I've grown to love turning them too. People get so excited over platters and plates. And there's nothing like eating off of a wood plate. You really don't need more than an inch of wood to make some great stuff.

Happy turning.

It's true that platters can be a very interesting turning experience, and there are many admirers who appreciate them.

As for finding local turners and clubs.......well, that can, and absolutely does work for many prospective turners, but is not carved in stone. There are a few turners who can become accomplished without that influence.......and, in the process could possibly find new ways of doing things that could set that person apart from the main group that learn the same techniques and procedures everyone else does. There is no right way and wrong way about considering this proposition, and is entirely up to the individual, and their driving ambitions.

ko
 
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I'm still having great results with DNA bath method, 2-4 weeks wait depending on how thick the walls and type of wood. I had couple check, but that was because I left the bag open.
 
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May try the boiling method and see how that works?

I hope I didn’t give the impression that boiling rough-outs leads to shorter drying time; I haven't see that in my experience. What boiling helps me with is diminished cracking in the drying process. I believe the wet heat relaxes the wood structure so that it is more flexible as the free moisture leaves the wood. Some woods are super-prone to cracking and boiling is about the only way I’ve been able to find success with them. However, boiling has not allowed me to accelerate the drying process.
 
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Boiling wood is supposed to rupture some of the cell membranes allowing the moisture
in the wood to more easily migrate to the exterior of blank. I have used a pressure cooker
to process some hollow form pieces in the past and had no problems. I also used a microwave
on several of these pieces to speed the drying process with success.
 
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I have been doing the DNA soak and wrapping the outside of bowls with paper to try to stabilize and speed drying for a couple months. It seems to be working well, definitely seem to dry faster. Some already seem dry after 6-8 weeks. Warping seems about the same, and cracking seems to depend on the wood.
 

john lucas

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All of that speed drying stuff just seemed too much of a hassle for me. I rough turn a few bowls and the turn a natural edge to completion to get my finished bowl fix. I put the rough turned ones up and do the same again later. After 3 or 4 months of this i had plenty of dry bowls. Then I would do sort of the same thing. Turn rough bowl, grab a dry one and finish it. I don't do many bowls anymore and still have blanks and rough outs in the shed for when ever I get the urge.
 

Bill Boehme

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All of that speed drying stuff just seemed too much of a hassle for me. I rough turn a few bowls and the turn a natural edge to completion to get my finished bowl fix. I put the rough turned ones up and do the same again later. After 3 or 4 months of this i had plenty of dry bowls. Then I would do sort of the same thing. Turn rough bowl, grab a dry one and finish it. I don't do many bowls anymore and still have blanks and rough outs in the shed for when ever I get the urge.

I wholeheartedly agree. The simple approach is so ... well, simple ... not to mention it's also free. :D I'm all in favor of free. :)
 
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Wood contains moisture in two places - the lumens, and on the cell walls. The first is called unbound, the second bound water. There are no ruptured cell walls with boiling for a number of reasons, chief among them being holes in walls to transfer water and nutrients laterally, second, no cytoplasm within the cells far beyond the living cells in the primary xylem. Folks boil the wood, and might get some benefit from the softening of the lignin, relieving some growth tension in nasty grain. Price is muddying the color a lot. Your walnut shimmers with secondary colors when air-cured, but is pretty universally brown when steamed in the kiln. Same thing. However, you can't get more water onto the cell walls than the fiber saturation level, so you're not hurting drying much there. When the unbound water's evaporated, and the bound water begins to, the wood shrinks. That's where the problems start. Idea is to smooth the transition from high relative humidity and saturation to low relative humidity and equilibrium with its environment come into play.

We can create a controllable minienvironment by bagging, the most common method of slowing evaporation. Bag, box, big container of similar moisture "Kiln" regulated to remove water slow enough to equalize through the wood but rapidly enough to keep it from molding.

We can coat the outside of our bowl with things that attract and hold water to keep them from checking. Liquid Dish Detergent - glycerol - is popular and pretty effective for the price. Bigger alcohols like PolyEthelene Glycol up to 1000, a solid at room temperature, both blocks the pores and attracts moisture, and is very effective. Ethyl/methyl alcohol -"DNA"- evaporates faster than water, and is therefore of no use. One I'm particularly fond of in the water-loving group, is potato starch. Rub into endgrain, like the Swedish spoon carvers.

We also use fully occlusive coatings like water emulsion wax Acrylics, or even latex paint. All more or less effective at slowing the loss, combining, to some degree, elements of the containment and expansion approaches..

But, the best thing to do is to realize that water moves through the tree through the endgrain, and is lost at up to a dozen times faster through it than through quarter, , or maybe 10 times faster than face grain, Turning to uniform thickness means nearly nothing, since it's the orientation of the grain which determines rate of loss, not thickness. Don't make a bowl too broad or flat in the bottom. Almost assured of trouble as the wood contracts, trying to make a smaller circle, and may overstress. If you need one like that, go to a surface dressing an mild containment.

All you want to bone up on - prepaid https://www.fpl.fs.fed.us/products/publications/specific_pub.php?posting_id=18102&header_id=p

Specifically on wood structure https://www.fpl.fs.fed.us/products/publications/specific_pub.php?posting_id=17963&header_id=p

Or how water is held and lost https://www.fpl.fs.fed.us/products/publications/specific_pub.php?posting_id=17964&header_id=p

EDITED BY MODERATOR TO REMOVE SNARKY COMMENT TOWARDS OTHER MEMBERS. IF YOU CAN'T BE CIVIL THEN TROLL SOMEWHERE ELSE.
 
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Bill Boehme

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Wood contains moisture in two places - the lumens, and on the cell walls. The first is called unbound, the second bound water.

The term for the first is more commonly referred to as "free" water. The bound water is a constituent part of the cellulose via hydrogen bonding which is the reason for the term "bound".

If you can't make your point without insulting others then please refrain from posting. We can struggle along without the benefit of that sort of input.
 
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MM gave you a very nice description of what and how things work. Listen to that advice. No one has asked you for your procedures you use, within every method there is more to it than just rough turning a bowl and throwing it into a kiln for example. There is a little bit of misinformation on roughing bowls and that is the 10% thickness rule, if you can call it a rule, and the even wall thickness rule. First the thickness has more to do with grain orientation and if you need the thickness for a special rim treatment. Now sometimes that is hard to determine when roughing so staying with the 10% generally is used and can be dried that way. The even wall thickness is in my opinion the killer of a lot of bowls cracking. You want fairly even wall thickness but you want the bottom of the bowl thinner (not even thickness and for sure not thicker than the sides). As the wood moves (warps) having a little thinner bottom will allow some elasticity so you won't experience as much loss. MM pointed out not having to flat or broad of a bottom, good advice, and I will add not to thick of a bottom.

So to wrap up a bit when using a kiln as you mentioned. First I am envisioning a household oven when you say you are using an oven. If this is the case a 75 watt light bulb is most likely way to much for the square footage in an oven. Maybe a 40 watt would be better. You might be bringing the temperature inside the oven up way to hot, way to early. Also do you have a way of drawing the door of the oven in really tight against the door seal. You may be allowing to much moisture loss to fast if you are not drawing that door in really tight against the seal. Are you anchor sealing the blanks prior to putting them into the kiln, you should it helps. These are just a few ideas that may help you with success.

One last piece of advice. When rough turning blanks we all have been told the biggest bowl is the money bowl. Therefore that gets stuck in our brain and most of us feel we need to preserve the blanks with the biggest bowl possible out of the timber. This advice needs to taken lightly. If you have some surface checks on your rounds you need to turn them off, everyone knows that. However to many people turn the check off until they cannot see it anymore and then they stop so they can get the largest bowl they can, money bowl remember. That is cause for many failures. Turn those surface checks out until you cannot see them and then another 1/2 inch at least, 3/4 inch to 1 inch is even better. There will remain microscopic checks that you cannot see after you remove the checks you can see, they must be removed or you will have failures.
 

odie

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There is a little bit of misinformation on roughing bowls and that is the 10% thickness rule, if you can call it a rule, and the even wall thickness rule. First the thickness has more to do with grain orientation and if you need the thickness for a special rim treatment. Now sometimes that is hard to determine when roughing so staying with the 10% generally is used and can be dried that way. The even wall thickness is in my opinion the killer of a lot of bowls cracking. You want fairly even wall thickness but you want the bottom of the bowl thinner (not even thickness and for sure not thicker than the sides). As the wood moves (warps) having a little thinner bottom will allow some elasticity so you won't experience as much loss. MM pointed out not having to flat or broad of a bottom, good advice, and I will add not to thick of a bottom.

Interesting about that 10% rule not being so much of a rule.....but, it's a useful generalized starting point for those who are seasoning woods for the first few times. (It's a good rule for that purpose, IMHO.) I've also come to modify the rule to be a little thinner at the bottom than the sides......but, the bottom is more closely adhering to the 10% rule than the sides. I'm probably closer to 10% on the bottom, and 15% on the sides......so, a little thicker on the sides. This even further extends the time element to fully stabilize the MC (moisture content), but the warping is less pronounced overall. They all eventually stabilize, but many of my rough-outs take a few more months to accomplish this objective, than do many other turners who stick more closely to the 10% rule.

Reducing the amount of the warp, greatly reduces the likelihood of cracking......and, that's always a good thing. It does require more time, and patience.......but, if you've got enough bowls being seasoned at any one time, it's less of a factor. The number of bowls being seasoned depends on the speed you produce bowls. For me, I generally have 30-40 bowls being seasoned at any one time. I weigh them monthly, and when there is no change in weight for 3-4 months, it's ready for finish turning. I haven't verified this with statistics, but I'd say my average number of bowls that complete the seasoning process per month, is around 5-7......and, that's close to the number of bowls I finish turn each month. That relationship between how many you finish turn, compared to how many are ready to finish turn per month, is the equilibrium figure for YOU and YOUR shop.

ko

This is a small Gabon Ebony roughed bowl (anchorsealed), and you can see the wall thickness is a bit more than 10% of the diameter.......what you don't see, is the bottom is thinner than the wall thickness.
IMG_2613.JPG
 
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john lucas

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A couple of things that helped me. Don't leave sharp edges on your rough turned pieces. These lose moisture faster and cracks often start there. Coat just the endgrain portions with wax or end grain sealer. If you use a tenon it will have sharp corners, and needs them. Coat the whole tenon with end grain sealer, a lot of checks seem to start there. None of these speeds up drying, they just help keep the bowl from splitting while it's drying.
 
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