Kiln for Once Turned Green Blanks

[Collin Clay]

My impression is that a lot of pro's like people in AAW are processing so much material that they don't mind air dry times for roughed out forms since they have giant stashes of blanks built up over time. But for amateurs like myself who only turn a few things a month, if you have interest in trying rapid drying I wanted to share my 2 cents from making a kiln. Namely I think this is a cost effective design which also mitigates fire concerns by using 5 25W bulbs with a controller. I have only been working with white and red oak in my area, but I find it to be highly effective at taking a green roughed out bowl to 10% MC in less than a week, without causing damage (unnecessary cracking, warping beyond normal drying results) to the final product.

EDIT: This is for twice turning bowls. When I say once turned blanks I mean that you have rough turned them once to 10% of the OD, which is typically around an inch thickness for bowls. I figured this was self evident since I've only heard of people kiln drying for twice turning, but I could have misled people to think I mean once turning to final form and then kiln drying

View: https://www.youtube.com/watch?v=HceLEBWc-00&t=517s&ab_channel=CollinClay

 

[Glenn C Roberts]

How do you vent the humidity?

 

[Emiliano Achaval]

For me is not a matter of drying it quickly. It's that kiln dry wood just doesn't cut as well or as easy as air-dry wood. KIln dry tends to splinter more. For some jobs that require precision kiln dry wood is a must. I do have a home made kiln, but there is no wood here that I can dry in a week, they would crack beyond help. I use my kiln to dry my box blanks, they take a few months.

 

[Doug Freeman]

Thin 3/8” or less 1 turn items only take a week or 2 to dry anyway. I’m just a hobbyist but I typically have 10-30 pieces in the pipeline drying. Its the 2 turn items that can take a while. The microwave method provides quick drying if I need something quick.

 

[Don Wattenhofer]

I just turned 5 red oak bark edge bowls about 2 weeks ago and weighed, left uncoated, not bagged or put in a kiln then after 1 week they had lost most of the moisture without without cracking or extreme distortion or loosening of the bark. The live tree was cut down late last fall and a 4 foot 12" diameter section of the butt log was put into cold storage as in outside.
So the question is what is the kiln for?

 

[Mark Jundanian]

My impression is that a lot of pro's like people in AAW are processing so much material that they don't mind air dry times for roughed out forms since they have giant stashes of blanks built up over time. But for amateurs like myself who only turn a few things a month, if you have interest in trying rapid drying I wanted to share my 2 cents from making a kiln. Namely I think this is a cost effective design which also mitigates fire concerns by using 5 25W bulbs with a controller. I have only been working with white and red oak in my area, but I find it to be highly effective at taking a green roughed out bowl to 10% MC in less than a week, without causing damage (unnecessary cracking, warping beyond normal drying results) to the final product.

View: https://www.youtube.com/watch?v=HceLEBWc-00&t=517s&ab_channel=CollinClay

Interesting idea to use the plastic box, Collin. Beats driving up and down the streets on garbage day looking for a refrigerator .

Do you think the desiccant beads are necessary? Have you tried your kiln without them? I like the idea of multiple 25 watt bulbs for spreading the heat source out and you're covered if one should burn out. With the 40 watt you're going to try you might replace some but not all of the 25's to get to the steady state you want to achieve. Where are you getting your incandescent bulbs? They are not readily available around here.

 

[Collin Clay]

How do you vent the humidity?

The desiccant beads absorb the moisture from the air

 

[Collin Clay]

For me is not a matter of drying it quickly. It's that kiln dry wood just doesn't cut as well or as easy as air-dry wood. KIln dry tends to splinter more. For some jobs that require precision kiln dry wood is a must. I do have a home made kiln, but there is no wood here that I can dry in a week, they would crack beyond help. I use my kiln to dry my box blanks, they take a few months.

I haven't had any issue with splintering while turning, haven't even heard of that before. I do understand species will respond differently to drying, all I can say is this works well for the trees in my area.

 

[Collin Clay]

Thin 3/8” or less 1 turn items only take a week or 2 to dry anyway. I’m just a hobbyist but I typically have 10-30 pieces in the pipeline drying. Its the 2 turn items that can take a while. The microwave method provides quick drying if I need something quick.

I twice turn everything. I played around with the microwave early on and it wasn't worth the trouble from what I saw. Having to do dozens of cycles, short bursts followed by waiting hours, measuring weight, for days and days. I'd rather toss it in a kiln and be done with it. I added an edit to the original post because I think I had been unclear that this is for twice turning. This dries roughed out blanks quickly, not just thin walled final forms.

 

[Collin Clay]

Interesting idea to use the plastic box, Collin. Beats driving up and down the streets on garbage day looking for a refrigerator .

Do you think the desiccant beads are necessary? Have you tried your kiln without them? I like the idea of multiple 25 watt bulbs for spreading the heat source out and you're covered if one should burn out. With the 40 watt you're going to try you might replace some but not all of the 25's to get to the steady state you want to achieve. Where are you getting your incandescent bulbs? They are not readily available around here.

I have not tried without the beads, the air in the box would become saturated and the drying process would slow down because the concentration of moisture in the wood vs the air would come together. Yeah theoretically the results of 3 40 W bulbs is approximately the same energy input as 5 25W bulbs 120W vs 125W. But that would give me approximately no change in the steady state temperature while increasing the risk due to the higher temperature on the bulb surfaces (though I'm not sure if it would be meaningfully more dangerous until I test it). If I did 5 40W then I would reach a higher temperature before it hit steady state, I'm not sure yet what it would be, or what bulb temps I would have. I'll have to try sometime for the heck of it. I got the 25W bulbs on amazon

 

[Randy Anderson]

When I first started I had same thought - I need to speed up the drying process to be able to finish something. Over time I realized it doesn't take long to build up a supply of drying pieces that you work from. I built and still have the typical small, fan and light bulb drying box. I never use it. I tried the microwave process a couple of times and didn't like it. I agree with Emiliano. I don't know why but I can tell when I turn a block of kiln dried wood and don't care for it. I spent a bit of time focused on turning traditional bowls thick, sealing and setting aside and standardized on the paper bag process for once turned natural edge. I was surprised at how soon I had a stack of traditional ready for final turning and natural edge ready for sanding. I don't weigh things. When they hit 13-14% on my meter on inside bottom center and bottom foot area I finish them out. All that said, oak is the most prone to cracking wood that I work with. Plentiful here so not hard to get more. Net, when I spent a couple of months focused on building a reasonable stack of drying items I then had a pipeline of things to choose from to finish.

 

[Collin Clay]

I just turned 5 red oak bark edge bowls about 2 weeks ago and weighed, left uncoated, not bagged or put in a kiln then after 1 week they had lost most of the moisture without without cracking or extreme distortion or loosening of the bark. The live tree was cut down late last fall and a 4 foot 12" diameter section of the butt log was put into cold storage as in outside.
So the question is what is the kiln for?

You say you cut the tree down ~ 6 months ago. This is about processing green, freshly cut logs. I haven't tried seasoning logs, in the end it's still waiting time whether you are drying blanks or logs. I'm not sure what MC you started with using a seasoned log, but obviously fresh green wood is not dry in the timeframe you describe, otherwise yes nobody would be using kilns or waiting 6mo-1yr to air dry roughed out blanks

 

[Collin Clay]

When I first started I had same thought - I need to speed up the drying process to be able to finish something. Over time I realized it doesn't take long to build up a supply of drying pieces that you work from. I built and still have the typical small, fan and light bulb drying box. I never use it. I tried the microwave process a couple of times and didn't like it. I agree with Emiliano. I don't know why but I can tell when I turn a block of kiln dried wood and don't care for it. I spent a bit of time focused on turning traditional bowls thick, sealing and setting aside and standardized on the paper bag process for once turned natural edge. I was surprised at how soon I had a stack of traditional ready for final turning and natural edge ready for sanding. I don't weigh things. When they hit 13-14% on my meter on inside bottom center and bottom foot area I finish them out. All that said, oak is the most prone to cracking wood that I work with. Plentiful here so not hard to get more. Net, when I spent a couple of months focused on building a reasonable stack of drying items I then had a pipeline of things to choose from to finish.

My personal issue with air drying is not even that I am impatient to get a final product, but that I am impatient to gain experience and technique. I didn't want to do nothing but roughing green blanks and waiting most of a year before I could experience the last half of the process and finishing (without paying $$$$ for dried blanks). Rapid drying has allowed me to gain significant experience on the entire process in a shorter time frame, and to develop a process from log to final bowl that I am happy with. I'm moving on to hollow forms now. I think over time I will likely begin to accumulate a stash since my eventual experience will not make me so hungry to practice. I notice people say that about oak a lot and I was confused at first because I had no problems with oak I was working with. Eventually I learned that I had my hands on white oak, with a T/R ratio of 1.9 which dries extremely well. Once I finally got red oak I learned why people had issues. I documented an example here

https://www.reddit.com/r/turning/comments/m51iny

View: https://www.reddit.com/r/turning/comments/m51iny/red_vs_white_oak_drying_movement/

 

[Russell Nugent]

You say you cut the tree down ~ 6 months ago. This is about processing green, freshly cut logs. I haven't tried seasoning logs, in the end it's still waiting time whether you are drying blanks or logs. I'm not sure what MC you started with using a seasoned log, but obviously fresh green wood is not dry in the timeframe you describe, otherwise yes nobody would be using kilns or waiting 6mo-1yr to air dry once turned blanks

I think there is just a slight confusion of terms there. Generally once turned means you've turned to finish thickness. Twice turned or roughed out is what you are doing i believe. If you turn to finish thickness then yes it can be dry even from fresh green in a week. In the end I think you and Don are talking 2 different things.

 

[Collin Clay]

I think there is just a slight confusion of terms there. Generally once turned means you've turned to finish thickness. Twice turned or roughed out is what you are doing i believe. If you turn to finish thickness then yes it can be dry even from fresh green in a week. In the end I think you and Don are talking 2 different things.

Yes thank you, this is all about twice turning. So the bowl blank will typically be around an inch thick (10% of OD). I haven't heard of anyone using a kiln on pieces they intend to once turn to finish and allow to warp, but I guess maybe someone would do that? Thanks for clarifying.

 

[Mark Jundanian]

@Collin Clay , if you have the time, it might be useful if you could note the particulars of your electronic switch.

 

[Collin Clay]

@Collin Clay , if you have the time, it might be useful if you could note the particulars of your electronic switch.

The manufacturer has an instructional video here, very easy to use

Amazon.com

 

[Mike Johnson]

The more time that a wood blank is given to dry allows the turned piece more time to stabilize as it dries and moves. If you force air across a drying piece of wood the outer surface dries rapidly while the internal wood is still damp. Depending on the species of wood you can speed up the process on some species and not others without incurring more checking and cracking, each species of wood is different and reacts differently to various drying methods.

 

[Randy Anderson]

Collin, completely understand. I'll share the advice I got from my local friend and mentor - treat your roughing work for twice turned bowls like it was a finished bowl. Don't just turn it all out to get to the thickness you need and not pay attention to technique, tool marks, form, etc. Consider your cuts for each pass as if they were finish cuts and use them to practice getting the routine and technique down. I did and still do. It helps.

 

[Collin Clay]

Collin, completely understand. I'll share the advice I got from my local friend and mentor - treat your roughing work for twice turned bowls like it was a finished bowl. Don't just turn it all out to get to the thickness you need and not pay attention to technique, tool marks, form, etc. Consider your cuts for each pass as if they were finish cuts and use them to practice getting the routine and technique down. I did and still do. It helps.

Good advice. I have had this thought, though I give myself some wiggle room. For example if it is convenient I may take non-supported cuts (i.e. rim to center on the bowl exterior) if they seem more manageable in the roughing stage. But I am mindful that I don't want to cause imperfections that make it to the final form

 

[Collin Clay]

The more time that a wood blank is given to dry allows the turned piece more time to stabilize as it dries and moves. If you force air across a drying piece of wood the outer surface dries rapidly while the internal wood is still damp. Depending on the species of wood you can speed up the process on some species and not others without incurring more checking and cracking, each species of wood is different and reacts differently to various drying methods.

Yep this is true. But to me the cost of waiting a year is so high that I will test each new species myself first and see if it can be accelerated or not. As a guideline I have seen that species with 2.0 or less T/R ratio can be accelerated with great results.

 

[Glenn C Roberts]

The desiccant beads absorb the moisture from the air

Must have missed the mention of the desiccant.

 

[Mike Brazeau]

I built a kiln about 10 years ago and used it initially to dry blanks from a Red Elm tree our guild made keepsake pieces for a cottage community nearby. It was the best thing related to turning I ever did. I have an article I did on it and another on Wood Processing I can pass on if anyone is interested. Just message me with your email address. It uses a light dimmer, a light bulb (I saved some years ago) and a 12 Volt computer fan. Principal is very simple, start temperature low, build humidity and raise temperature gradually. Temperature rise in some ways starts to happen anyway as less energy goes into vaporizing the water in the wood which is of two types. First is interstitial or extra cellular water and the second water bound in various cells. Attaching a couple of photos from some small apple boards I dried for a fellow guild member used for a staved urn. I have second turned natural edge bowls in as little as 12 days. They do not look round anyway and a small amount of movement is not an issue.

 

[Collin Clay]

I built a kiln about 10 years ago and used it initially to dry blanks from a Red Elm tree our guild made keepsake pieces for a cottage community nearby. It was the best thing related to turning I ever did. I have an article I did on it and another on Wood Processing I can pass on if anyone is interested. Just message me with your email address. It uses a light dimmer, a light bulb (I saved some years ago) and a 12 Volt computer fan. Principal is very simple, start temperature low, build humidity and raise temperature gradually. Temperature rise in some ways starts to happen anyway as less energy goes into vaporizing the water in the wood which is of two types. First is interstitial or extra cellular water and the second water bound in various cells. Attaching a couple of photos from some small apple boards I dried for a fellow guild member used for a staved urn. I have second turned natural edge bowls in as little as 12 days. They do not look round anyway and a small amount of movement is not an issue.

Thanks for sharing, I agree it is great to do these kinds of experiments even just to get a better perspective on the process. The kiln I have here will be much more aggressive due mostly to the desiccant, the air will be very dry in the trapped volume and that moisture concentration difference greatly increases transfer rates at the surface. Also my temps are higher and this fan blows much harder than a computer fan. Your results give some good perspective, since you accomplished stable dried pieces in two weeks even with a more gentle process.

 

[Don Wattenhofer]

You say you cut the tree down ~ 6 months ago. This is about processing green, freshly cut logs. I haven't tried seasoning logs, in the end it's still waiting time whether you are drying blanks or logs. I'm not sure what MC you started with using a seasoned log, but obviously fresh green wood is not dry in the timeframe you describe, otherwise yes nobody would be using kilns or waiting 6mo-1yr to air dry roughed out blanks

The wood was not seasoned it was frozen shortly after being cut down and held that way until mother nature un did my freezer.