Green Bowl Drying?


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I have started turning more green wood than dried.

There seems to be a million different theories out there on how to dry to reduce checking, splitting, and warping. I assume most folks are like me, and don't really want to wait 6-12 months for the rough turned bowl to dry before finishing. There has to be a better way!

I have a small homemade kiln, but I can't seem to find the right amount of air dry time before baking. I had one bowl that air dried for a week or so, and then I tossed into the kiln for about 24 hours and it was perfect. Slightly mishapped, but easily trued furing the final cutting.

My next attempt, I went right from the lathe to the kiln...that didn't end well. Pretty firewood though!

I tried again with a larger bowl, that I air dried for a week, and then just placed in the unheated kiln (fan on, no heat) overnight, and that one checked pretty bad.

I am starting to think I need to treat the end grain with something, but I don't know where to start. Does a basic sanding sealer work? Do I just need to be more patient?

Any advise would be greatly appreciated.

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Put the green turned bowl in a plastic bag with the wet shavings. Every few days take it out and weigh it. Bag can be just casually folded over, not tightly closed. When the weight of the bowl is stable for a week or more then you can try the kiln.

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honestly i didnt have much luck with bag drying they all cracked on me i think the bags dried out too fast or they stayed too wet. then i tried the paint sealing but that didnt work eather. then i tried making my own parafin wax sealent but it was messy, had to bring my own crock pot to keep it melted and i still got some checking not bad but some. you can soak it in alchol but i didnt like that expensive and kind of messi have heard you can boil the wood to get it so the wood ruptures evenly then you dont have to worry about warping or cracking. david marks has a similar set up for his shop where he boils his wood in large drum. http://www.thewoodwh...s-gallery-tour/ but this is time consuming and can be expensive. but if you are using a 150 doller piece of wood they you want to make shure you dont waste you money. he talks about his process for the first 4 min of the movie

best thing i found was anchor seal the bowls that i coated warped a bit but that is to be expected but none cracked or checked. works like a champ no real problems and the gallon is alot but the first time your budy says hey i got this tree you will use up half of it real fast. its all caned and ready to go no heat to melt wax, just open the can and wipe it on. still takes time for the bowls to dry but they wont get destroyed on you......sometimes you have to wait for nature to do what it wants so that you can make what you want. be patient the bowls will dry out.

here is gallon $22http://www.amazon.co...ords=anchorseal

here is quart $11 http://www.amazon.co...ords=anchorseal

if your family wants a bowl now why dont you try your hand at segmented turning. you could make some simple turning blanks just by glueing different woods face to face and then turning it round. here is my first attemp at mixing wood of different sizesDSCN0224.jpgDSCN0226.jpg

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i usualy slop on everything that is not covered in bark anchor seal works just like the bark it allows the wood to slowly dry out. but once you make the rough bows with the sides thined out so it wont take a full year or 2 too dry out only 6 months or so. you could coat just the end grain but from what i understand it does not hurt it to wax the entire surface so to be safe i wax it all. i let it dry over time. like i roughed out a bunch stacked them and forgot about them in a dry cool place. and i worked on glued together bowls and pens and ect.... mostly small stuff untill i could get back to the solid wood bowls.

like i said you can rush it a bit but then you end up with a larger percentage of your bowls being broken or severly warped. rather not rush it and have a much much smaller amount of bowls stay true.

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Another thing to consider is that the type of wood matters some woods will split much more readily than others. Oak, walnut & pecan all seem to split badly for me. Apple and pear don't.

The best way to overcome this problem is just to build up an inventory of drying blanks. Ruogh turn a bunch of blocks, put on the anchorseal and put them on the shelf. After a few months, you'll have blanks ready to turn.

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Thanks for all the input.

I was hoping there was a 2-3 week solution, but it seems 2-3 months is about the best I can hope for.

I will do some testing with the sealer and the kiln to see if I can't shave off a few weeks, and update if I find anything consistent. I just added an RH monitor to the kiln, so hopefully that can help me to know when to progress through the stages of drying.

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A couple of ideas...and I am assuming you are rough turnign your bowls to reduce the thickness that needs to dry and increasing the surface area that can dry.

1) just turn it and finish it. The bowl will warp in all manner of wackiness. The end up being very cool. Richard Raffan preaches this.

2) Don't use a plastic bag, use a paper bag. It will slowly let the piece breath. I have had good luck with this, but never went that route working on a timetable.

Here is a thread I had from another forum that had some really great advice...

http://www.aawforum.org/vbforum/showthread.php?t=9277

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Both great posts, thank you!

However, the one thing I have found is that no one has a very repeatable, "scientific" process. Which may just be a curse of woodworking, or not taking the time to log success and failure, but instead just finding what works for them (which by volume seems like rough it and forget it for several months). I am a very logical person though, and I am hoping to come up with a consistent, repeatable process that can be shared so others hopefully won't have to go through many wasted blanks. This may just be a pipe dream, but we'll see!

The goal is to have a process involving drying times, RH, moisture content, and tempuratures throughout the drying process to determine when to move from step to step.

After reviewing a mass of online forums it seems the concensus is that the process should involve:

1) Rough Turning Green

2) Sealing if Air drying, or packing in a brown bag with shavings for some period of time (I hope to find an RH or Moisture Content, rather than a time, since wood species, size, and thickness will greatly very time)

a) Most stop here, and just let time do it's thing...a lot of time. I am hoping to reduce some time by adding a few steps.

3) Placing the Air/Bag dried bowl into the kiln and turning on the fan, again until a desirable RH/MC is achieved

4) Turning the kiln on thus increasing the tempurature of the Kiln to achieve a desired RH/MC that is considered "Dry" for finish turning and finishing.

I am targeting a moisture content of ~8% since that is what the local mill considers "Kiln Dried" lumber, which I have had plenty of success and consistency with.

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only thing i can sugest is when you start drying pick a species like maple measure the moisture, weight and date you started. you will have to get this as soon as the tree is cut down. write it on the bowl. then over the next year or what ever till its at the desired 8% moisture keep track of each different bowl. only difference i can see is that you are kiln drying where as most turners put it on a shelf and pretend it not there.

so have a control which would be the bowl in a bag or sealed and left outside to air dry.

and the experimental which would be the one in the kiln which would be in a bag or a seal coat just like the control.

you will have to do this with several hundred bowls of each species to come up with a consistant measurement for each type of wood.

the varibles you will run into are -the time of year the tree is cut down,temperature, that years rainfall, the rainfall of the trees lifetime, age of the tree, health of the tree, how fast you measured the bowl blanks after tree was felled, species of the tree (i think there is around 30 commonly used maple speices for lumber most can only be identified from there leaves)

to do this scientifily and perfectly you would need to grow one particular species of tree from scratch in a hermedicly sealed environment so you can control temp, health, and moisture....................so what are you doing for the next 60-80 years?

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Wood moisture is wood moisture, regardless of species or location. I have no intention of being spot on to the .01%, but I would think a target range per species should suffice. In theory, I suspect there is a range of moisture depletion that is going to blemish each species, and one that won't. The rest is just math based on your starting, and desired ending points. I highly doubt there is going to be significant difference in the drying of a maple blank from 40% to 8% between variations on the species. Perhaps I am very wrong though. I suspect if I tried hard enough to find the exceptions, they exist, but using the 80/20 rule, I would think I can find an ideal moisture depletion rate. I would further hypothesis that it will be close for many species. I plan to use Cherry, Walnut, and Maple as my test samples, because it is relativley inexpensive and available in my area, and I just like them, so I will get use out of them.

For Example: If you know dropping the moisture content of say maple, 10% a week (month, year, whatever) will crack it, but 6% won't, then everything else is just math from your starting point to your dried wood. The kiln just offers the flexibility to control all the conditions, heat, humidity, and airflow to make sure you achieve a targeted moisture depletion rate. I know many folks don't have a kiln, but they can be constructed very inexpensively. Mine is 2'x2'x4', and I have <$100 in it (most of which was the thermometer/hygrometer combo, because I wanted one I could monitor from my living room with the kiln in the basement)

This process has to exist already, or our hardwood dealers couldn't kiln dry their lumber. I suspect they just know what works for them in their area, and have not interest in doing the math each time.

I guess the goal isn't to find the perfect formula (though I would like to) but instead to find how far I can push it without ruining the wood. Rough it and forget it probably works for many, but I know it won't work for me. Perhaps all I will find in the experiment is that specific parameters aren't readily available for a reason.

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The key to drying wood without splitting is not so much the speed of drying - it's the even-ness of the drying. Lumber processors typically work with long sticks that have a large side grain to end grain ratio. End grain loses moisture more quickly than side grain - setting up the stresses in the wood that cause splitting.

Woodturners are typically working with small blanks that have a small side grain to end grain ratio. That is why it is difficult to dry without splitting. Moisture flows out of the end grain easily, levaing the blank with a larger moisture content differential between the center and the edges. This makes for more internal stress and more splitting. If you slow down the overal drying process, it eases this problem.

Rough turning the bowl can help with this problem because there is more surface area in the side grain to spead drying there and there is less material to stress.

There really is no magic bullet here except for patience. Even kiln dried lumber that hasn't split still can have alot of stress. I suspect many of us have experienced a kiln dried board releasing tension when cut.

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The key to drying wood without splitting is not so much the speed of drying - it's the even-ness of the drying. Lumber processors typically work with long sticks that have a large side grain to end grain ratio. End grain loses moisture more quickly than side grain - setting up the stresses in the wood that cause splitting.

Woodturners are typically working with small blanks that have a small side grain to end grain ratio. That is why it is difficult to dry without splitting. Moisture flows out of the end grain easily, levaing the blank with a larger moisture content differential between the center and the edges. This makes for more internal stress and more splitting. If you slow down the overal drying process, it eases this problem.

Rough turning the bowl can help with this problem because there is more surface area in the side grain to spead drying there and there is less material to stress.

There really is no magic bullet here except for patience. Even kiln dried lumber that hasn't split still can have alot of stress. I suspect many of us have experienced a kiln dried board releasing tension when cut.

So if this is the case, why wouldn't the prefered method be to turn completely green (vs just roughing green), since a thin bowl in theory would release moisture the most evenly? I am not saying your wrong, I am just trying to understand all the mechanics. I was assuming it is a mix of speed and evenness. So may plan was to seal the blanks (to help with evenness) and then add airflow and heat to control (accelerate) the speed.

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if you make it too thin it will warp too much

if you want a even thick bowl then you want to leave it a little thicker and then when it is fully dried and done warping you can put it back ont he lathe and true it back to being a circle.

i think that all you can do is experiment with the bowls trying different temps and humidity but justsomeguy had it basicly spot on if you dry out the wood too fast the wood will split. most boards do that and the lumber mill just cuts off the last few inches but with a bowl blank the end couple inches is half the bowl. its the end grain that splits on you because it loses moisture so much faster then face grain. when the bowl is half end grain you can expect half the bowl to crack or check. i dont think there is realy a science to this if a company makes enough bowls they eather just dry out massive amounts of bowls and use the ones that survives so if they lose 5% oh well. or they turn wet wood to final demensions and dont care if it warps. or they dont sell in large enough quantities that they can rough out some bowl stack them for a year and then start making a year later and just make a new set for the following year.

if you want you can turn a green bowl to a final project. I have seen some turners who turn bowls wet realy thin they then put them in a microwave with a bowl of water to make the wood fiber more flexible and then they will twist and pull the wood to make it bend. that way they can give the wood a spout to poor out off. or to give the bowl a natural curved shape. the trick is that if its thin enough like you said it wont crack but it will warp alot so you want to find a happy middle ground where its not to thick and its even from top to bottom but it still thick enough to keep most of its shape so when you true up your blank you wont cut through your bowls wall.

this is a article on warped wood turning.

http://www.finewoodworking.com/how-to/article/green-turned-bowls-working-with-warp.aspx

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So if this is the case, why wouldn't the prefered method be to turn completely green (vs just roughing green), since a thin bowl in theory would release moisture the most evenly? I am not saying your wrong, I am just trying to understand all the mechanics. I was assuming it is a mix of speed and evenness. So may plan was to seal the blanks (to help with evenness) and then add airflow and heat to control (accelerate) the speed.

It depends on the circumstances. In most cases, you won't be turning it thin enough to do this. If you tunr it too thin and it still has significant moisture, you will almost guarantee that it will split. By rough turning, you are attempting to speed up the process, not eliminate it entirely. As it dries, the bowl will move even if it doesn't split. The extra thickness gives you the room to re-mount it on the lathe and turn it true.

I have turned bowls very thin from green wood, but they don't stay round. In fact, they end up wavy edged. I first saw this in Del Stubb's video on Bowl Turning. It makes for some interesting - if not all that useful - bowls.

The only wood that I have successfully and repeatedly turned bowls directly from green wood is Bradford Pear. Something about the structure of the wood allows it to release moisture very easily. It flys out of the wood on the lathe due to centrifgual force. It makes everything in the line of fire wet (me, the lathe, the wall, the floor, etc.), but the bowl is dry enough to retain it's shape when I'm done.

The sealer will help even out the the drying of the blanks. It's the a good way to balance speed and blank preservation.

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I think even if you did find a "golden rule" it would only apply to you, and more to the species you turn, my shop in my basement in PA, my ambient humidity is between 10-12% , but take for instance Marc who lives in Az is close to 0%. And methods of air drying speed will vary greatly.

If I were you, I'd find a tree service and have them drop a log for you to whack up. Giving you plenty of experiments. And just start trying everything. Start your long term pieces first. You may even find by the time you done running the short term blanks that your long terms are ready.

I use the 10% rule? Every inch of width across the bowl I leave 10% of an inch of thickness on the walls of the bowl. Stick in a paper bag of shavings and write the date on it. I'm at about 2 months before most are good to go. And about 90% sucsessfull, even with burls.

I would like to try the boiling thing though.

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I haven't tried it myself, but I read up on a process of soaking the green rough turning in denatured alcohol for 2-4 hours, then putting it in the bag with shavings like you normally would. After about 2-3 weeks, the weight will stabilize and you're ready for final turning.

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I haven't tried it myself, but I read up on a process of soaking the green rough turning in denatured alcohol for 2-4 hours, then putting it in the bag with shavings like you normally would. After about 2-3 weeks, the weight will stabilize and you're ready for final turning.

This is interesting. I haven't seen much on this method, but 2-3 weeks would be far better than any sealing/drying method I have tried, or read about.

What do you use to soak in? Do you do more than one bowl at a time? Is there risk to over soaking, or is the goal to fully saturate?

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My understanding is that wood goes through two stages of drying. The first is evaporation of water between the cells. This is relatively rapid, on the order of weeks. The second stage is evaporation of water from within the cells. This is much slower, on the order of months. Perhaps using the alcohol method the alcohol replaces the water in the cells and allows it to dry more quickly and more evenly. I would think that one would have to fully saturate the piece for the alcohol method to have an even effect.

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  • 1 month later...

I have found a process that is kind of a mish-mash of different things that seems to be working pretty consistently.

 

1) All wood that is obtained green is coated in Anchorseal II, until I am ready to deal with it.

2) Blanks are then rough turned to approx 1"-1.5" thickness throughout. (Not counting the foot, for jaws to clamp to, that's an additional ~3/8 of material)

3) The rough'd blank is then soaked in a bowl of denatured alcohol overnight, at least 8 hours.

       a)  I will try to add follow up posts with some pictures, when I remember to take a picture throughout the process.

4) Place the pre-soaked blank into a brown bag with wood shavings for 1-2 weeks.  It takes two weeks in my basement in WI, but I would guess that will change based on your climate.  My basement averages 60-65F and 28-33 RH.

5) Move into the kiln, for 1 week, run at ~85 F.  RH Typically peaks at around 75-80 and then drops to 8-12 when all is dry.

 

Total dry time from roughing is ~3 weeks +/- a few days

 

I will try to follow up with more information on both the DA soaking and my Kiln in case anyone is interested.

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  • 4 years later...

Chris h, I am a dry kiln operator and dry 14+ million bft of lumber a year. Each species has a different safe moisture loss rate and a different schedule to achieve this. Soft maple safe loss is 13.8% a day while red oak is 3.6% a day. Mixing species in a kiln you have to respect the species with the lowest safe loss. Ash, cherry and walnut do well together. But the walnut has tylosies that will drag it out at the end of the run. Use your heat and rh to set an emc. Check your losses daily and lower the emc of the kiln until the weights don't change at an emc of 8%. 

I do take rough turned bowls to work and put in the kilns. They do OK, I have had a few crack but it happens. You can get kiln schedules from they kiln operators hand book. They are not the schedules I useprofessionally but they are a good starting point that won't check your lumber.

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