Has Anyone Used A Bowl/Vase Kiln?

[Mark Kallemeyn]

Hello - I built a kiln to speed up my drying process of my green turned bowls & vases.My first attempts at this are not working out very well.I turned some cherry logs into vases & have tried different fan times & temp.They all split very bad.Hope someone can give me a little insight to make this work for me.Any info will be appreciated! Thanks Alot Mark

 

[MichaelMouse]

Hello - I built a kiln to speed up my drying process of my green turned bowls & vases.My first attempts at this are not working out very well.I turned some cherry logs into vases & have tried different fan times & temp.They all split very bad.Hope someone can give me a little insight to make this work for me.Any info will be appreciated! Thanks Alot Mark

You must control relative humidity. First item to purchase is some means of measuring it, then you have to establish a schedule of RH reductions and venting. Browse on over to http://www.fpl.fs.fed.us/ and do a search for The Wood Handbook to get information on moisture content as it relates to relative humidity, and then take a look at some of the kiln information. Make your own means of warming/venting, to get steadily decreasing or step down relative humidity. Humidistats are pretty pricey, so you will have to pay attention and work your way through the first charge or two.

 

[Wayne Spence]

Drying bowls and vases

Remember that the air passing over the surface is what dries the wood. The drier the air, the more ability it has to remove water. Whatever your ambient humidity is at todays temperature will determine how many grains of water the air holds and how much it can remove which would be the saturated number of grains minus what the air holds at that humidity and temperature. There are tables that will tell you this but I don't know if they are necessary when drying wood. I have built a couple of wood dryers and many commercial clay dryers. The release of water from the two is somewhat chemically different and the relation of water loss to shrinkage is different. In clay the initial loss of free water surrounding the grains results in a lot of shrinkage and danger of cracking. In drying wood no shrinkage occurs (if I remember correctly) until the free water is lost and you start losing the water bonding the fibers, lignin, etc.

To make it short watch how much air you have flowing over the surface. You must maintain somewhat of an equilibrium condition.

I hope I have not made this too complex and confusing. If so ignore it.

Wayne

 

[john lucas]

What are the shapes, how thick are they, are they a consistent thickness throughout, where and how are they cut from the log. Has the wood been sitting very long. All of these things affect how they dry.
speeding up the process with a dryer I would think would only compound any problems that already exist.
Cherry has been one of the most difficult woods for me to dry when left thick such as doing twice turned bowls. I've had very good luck when turned to 1/2" or thinner as long as it's a very consistent wall thickness and doesn't have the heart or any knots in it.

 

[Mark Kallemeyn]

What are the shapes, how thick are they, are they a consistent thickness throughout, where and how are they cut from the log. Has the wood been sitting very long. All of these things affect how they dry.
speeding up the process with a dryer I would think would only compound any problems that already exist.
Cherry has been one of the most difficult woods for me to dry when left thick such as doing twice turned bowls. I've had very good luck when turned to 1/2" or thinner as long as it's a very consistent wall thickness and doesn't have the heart or any knots in it.

Hi John - The cherry was turned lengthwise with pith & knots,wall thickness was aprox .75" to be returned.Base was aprox.2" the outside was wax sealed.I usually do the same thing & put in plastic bag & take out for 1 hr.every day & it usually drys in 3 mo.I have 2 computer fans in the box w/vents 2 light bulbs for heat.I'm thinking maybethe wood I used (cherry) is my problem. But from the sound of it from the other guys I need to get a little more scientific approach. Thank you Mark

 

[Wayne Spence]

Drying

Mark-I think John is right about using an empirical method just trying to reduce the rate of drying gradually. If you were drying 100 bowls a day it might be worth figuring out. Why not try reducing your fan speed or volume of air to one-fourth and keep the temp at room temp if possible. Also try some other types of wooden bowls. I don't know much about the drying characteristics of cherry, I don't like the stuff.

Advice of a would be sage. You can't change mother nature (drying in a paper bag is not natural either) but you can manipulate her.

 

[john lucas]

Mark By turning lengthwise do you mean just taking limb or log and turning the vase with the pith in the bottom. If so it's very difficult to prevent it from checking unless you dry it very slow. If you turn the same vessel from a piece of the log outside the pith area then your chances are greatly enhance.

 

[Mark Kallemeyn]

Mark By turning lengthwise do you mean just taking limb or log and turning the vase with the pith in the bottom. If so it's very difficult to prevent it from checking unless you dry it very slow. If you turn the same vessel from a piece of the log outside the pith area then your chances are greatly enhance.

Yes John I understand that but I have done this in the past with good results.I have not done this before with a fruit wood or with a kiln.I have always slow dried but I wanted to try a kiln.I have not tried any other wood in my kiln yet & that is why I am looking for advice.I guess I need to experiment (use the empirical method)by the way I had to look that word up.As you can most likely see this is my first time posting on a forum Thank You All for your time & patience.I think I will just fire up my old 90 & turn a while. By Now Mark

 

[Tony Latham]

I watched an interesting TV documentary called "How It's Made" and the subject was mass producing wooden bowls... When I say mass producing, it looked like a family operation. They would core out multiple bowl blanks from the green half logs... They sure were not using the 10% rule that a lot of us use for our twice turned bowls. But these were once turned bowls. The only lathe work was the coring.

Once they were cored out they were STEAMED and then kiln dried. They mentioned the steaming was to get the moisture consistent throughout. No mention of kiln conditions.

After kiln drying (and the wood they were using was cherry BTW), they sanded the top flat, another flat was sanding on the bottom and the insides and out were sanded with a special belt sander that appeared to be somewhat roboticaly operated... I forget the oil finish they used.. it may have been mineral oil.

Anyway, it was the steaming that got my attention. You'd think a green log would be evenly wet throughout...

L

 

[MichaelMouse]

Yep, Holland Bowl Mill. http://www.hollandbowlmill.com/ Not sure that there's any good science to "equalizing" the moisture, what with the inevitable difference when drying. Since the wood is fully expanded at the fiber saturation point, which is about 30%, one would think steam can do no more. Might get the lignin loose, which is what counts in boiling or steaming, in my opinion. That, and something more important in a bowl factory, equalization of color.

I microwave occasionally. Generates steam from within. Imagine the outside is already dry(er) because of the spinning.

 

[john lucas]

Did you also notice that they had to flatten the rim and bottom because of warp. I frequently turn large bowls to 1/2" thickness and let them warp without problems. It's the twice turned bowls that I leave thick that give me the problems. I don't have the best place to dry things.

 

[MichaelMouse]

Seems logical, given that wood can only contract upon itself, doesn't it? Thicker the sides, more the distance in uninterrupted wood to contract upon itself. Of course, I wouldn't mention it to anyone else, because you might catch the same as I got when I mentioned and demonstrated it with pictures.

The ten percent "rule" probably gets more people in trouble than it gets out.

Perhaps it was alcohol "drying?" You poured a Leinenkugel's after your roughing session?

 

[jerry w kowalski]

home made kilns

Mark,

I have been using a home made kiln for about 6 months now with very good results. I use 1 light bulb in the bottom and 1 fan at the top to draw the warm air over the bowls, usually they are dry in 3 week;

For fruit woods I use a slightly different approach, I turn the fan only on for 1 week, then the fan remains on with the light bulb turned on for 12 hrs per day, and the last week the fan and light are on contiually. Sometimes it takes an extra week to dry them this way. I don't use any wax sealant at all, and you could vary the stregnth of the heat source by using different wattage light bulbs.

 

[Steve Worcester]

Not sure that there's any good science to "equalizing" the moisture, what with the inevitable difference when drying. Since the wood is fully expanded at the fiber saturation point, which is about 30%, one would think steam can do no more. Might get the lignin loose, which is what counts in boiling or steaming, in my opinion. That, and something more important in a bowl factory, equalization of color.

I microwave occasionally. Generates steam from within. Imagine the outside is already dry(er) because of the spinning.

I don't know why, but steam is used in some really fickled woods (Pear) and yields excellent results. My guess is it is like a steam bath, just relaxes everything.

 

[Barbara Gill]

When I first started turning I built a kiln out of an old freezer. I used a light bulb, computer fan and a temp. sensitive switch. It worked fine; there was almost no cracking and minimum warping (I just kept the drying time slow and the temp low at first). I never used a drying table relative humidity charts, etc. I filled the kiln each time rather than just dry a few things because it is important to keep the moisture high when you first start. As with any drying of wood you should not rush the drying especially at first.

I don't use it any more as it was more trouble than it was worth.

 

[MichaelMouse]

I don't know why, but steam is used in some really fickled woods (Pear) and yields excellent results. My guess is it is like a steam bath, just relaxes everything.

When we made snowshoes we could put a wavy piece (waves along the grain) in the steamer and remove it virtually straight, that's for sure. After forming, it stayed that way through drying, which I consider presumptive evidence that the effect is does not persist through the drying process.

 

[odie]

I've never used a kiln, or any method of speeding up seasoning of roughed bowls. My success rate in getting dry roughed bowls has been very good.....over 95%, I'd imagine. I use weight as a means of determining stabilization, completely cover the blank with anchorseal, weigh once a month, three months with same weight=stabilized. Seasoning is seldom less than 6mo, and over a year is not uncommon........but I have a continual supply of roughed blanks, and use commercially kiln dried wood to fill the gaps........

So, tell me.......is there any benefit to kiln drying, other than the time factor?

I realize, of course, that most of us get antsy to get past the seasoning period.....that would only be natural, but something that must be taken into consideration.

.....but, if one were to have a constant supply of "in progress" roughed bowls.....wouldn't allowing for slow seasoning methods be the best overall game plan for giving oneself the supply he needs?

That is......if there is no conceivable benefit other than the time element.....

ooc

 

[Wayne Spence]

Mark

The latest issue of Woodturning Design #24 has an article on a homemade bowl drying kiln. This person used an old refrigerator. Look it up.

 

[odie]

When I first started turning I built a kiln out of an old freezer. I used a light bulb, computer fan and a temp. sensitive switch. It worked fine; there was almost no cracking and minimum warping (I just kept the drying time slow and the temp low at first). I never used a drying table relative humidity charts, etc. I filled the kiln each time rather than just dry a few things because it is important to keep the moisture high when you first start. As with any drying of wood you should not rush the drying especially at first.

I don't use it any more as it was more trouble than it was worth.

Hi Barb......

If I understand correctly what you're saying here......it's best to fill up the usable space within the fridge (kiln) with all unseasoned bowls, and dry them as a batch......?

That would necessitate a coordinated effort to turn all roughed bowls at approximately the same time......right?

If so, I can see how that might be a limiting factor in one's decision to even bother with a kiln........

ooc

 

[Barbara Gill]

Hi Barb......

If I understand correctly what you're saying here......it's best to fill up the usable space within the fridge (kiln) with all unseasoned bowls, and dry them as a batch......?

That would necessitate a coordinated effort to turn all roughed bowls at approximately the same time......right?

If so, I can see how that might be a limiting factor in one's decision to even bother with a kiln........

ooc

It didn't take very long to fill the space. If you only turn a bowl every once in a while it would take a long time.

 

[odie]

It didn't take very long to fill the space. If you only turn a bowl every once in a while it would take a long time.

I'm not sure I understand, Barbara.....

What you are saying is you don't have to fill the fridge kiln with roughed bowls all at once.....is that correct? If that is the correct assumption, then what would you say would be the best time frame to fill it for a batch drying session.....and how many bowls are you talking about?

How much time would you estimate is the average savings in time to season roughed bowls.

Can it be assumed that individual bowls within a batch are stabilized at different rates, depending on species, size, thickness, original moisture content, etc?......or, are they pretty much all the same moisture content during the seasoning process, depending on ambient humidity within the kiln?.....and, if that is so, then can it be assumed all the roughed bowls are finished stabilizing pretty much at the same time for the entire batch?

What sort of surface preparation are you using? Anchorseal? Bags? .....or ?

You mentioned that your home built kiln was more trouble than it was worth......could you be a little more specific as to why you feel this way?

ooc