Homemade Kiln

[RandyinLangley]

I did a quick search and came up with nothing in the archives. I'm pretty sure posting in the milling forum would be a good place to ask the question.

Have any of you built home made kilns? If you have what have you built and why? I originally thought a solar kiln would be the best idea since I could put it at the far end of my yard facing south for max exposure. The issue with this is it's a pretty far run for electrical if I'm going to run fans in it as well as being on the West Coast of BC we get about 4 months of sun and the rest is either rain or overcast so the kiln would only be good for that time.

I'm not looking to build a kiln to dry wood to sell, it's mostly going to be for the wood Nikko and I mill as well as possibly some turning blanks if they don't fit in the microwave. With the recent adventures of the Beech we had a hard time finding a kiln that would dry the slabs for a reasonable price. In the end we did find a place however through the process of looking the decision was made to build our own kiln.

I've surfed the web and found considerable information but I'm more interested in the information that isn't readily available from people who mill wood as a hobby / addiction and have gone throught the paces.

Looking forward to seeing pics as well as reasons.

 

[BobL]

I wouldn't call my setup a kiln but more of a drying shed. My setup is described here. I'm only getting about 7 to 12 F higher than external temperatures but given that we have a fair number of days of summer over 90F that seems to have done the trick, because it has dried most of the 2" slabs I put in there ~8 months ago to about 16%MC. I know I can get higher temperatures by reducing the air flow through the container but I already have more timber than I can poke a stick at so I don't want to cause any unnecessary checking etc. The documents I have read on the definitely recommend some form of forced internal circulation and keeping a solar kiln as full as possible so that it maintains its own thermal inertia.

 

[Al Weber]

See the following as a starting place.

www.woodweb.com/KnowledgeBase/KBPPKilnConstruction.html

 

[TNMIKE]

go solar

http://owic.oregonstate.edu/solarkiln/plans.htm

 

[RandyinLangley]

Very interesting read Bob. I suspect with information like that this little project of mine is going to get out of hand and I may end up incorporating an automated controls system if Nikko has any involvement.

 

[ebath]

Have any of you built home made kilns? If you have what have you built and why?


Randy,

I built a solar kiln this spring based on the Virgina Tech plans. I made two structural changes: 1) The foundation is a pole building 2) The fans are solar attic vents.

I am unloading my first charge this weekend. It is a mixture of quartersawn and plain sawn 5/4 white oak. It has been in the kiln for forty five days. It was loaded into the kiln the same day that it was felled and sawn.

It is beautiful wood and below 10% moisture content!

If I were building the kiln again, I would not use a pole structure. There is redundancy in the framing that requires additional time and materials.

I definately would use the solar fans. Although they are expensive, they are extremely easy to use.

Good luck with your adventure. I'm having great fun with mine!


Ed

 

[dustytools]

http://www.woodscience.vt.edu/about/extension/vtsolar_kiln/ Here is a link to the Virginia Tech solar kiln if you are interested.

 

[Backwoods]

Today at the tree school on the Umpqua, I was taking a class on the practical science for portable sawmill owners (part 1 milling, part 2 drying) I was talking the man that designed and built the solar kiln for Virginia tec. He told me not to build one with his design because it had too many limitations. To start with, it could only be 8’ wide to fit on a trailer. This also made it hard to load. He told me that Gene Wengert with the University of Wisconsin had designed and built a much better solar kiln.
http://owic.oregonstate.edu/solarkiln/plans.htm
Place your collector at you longitude plus 10. For example I am at 44* longitude so I would place the collector at 54* so that I would collect more heat during the winter months. I am getting everything together to build one using sawdust for insulation and a wood furnace as a back up heat source. That can be loaded with a forklift. The problem that I have is that the best place to build it is where I got my forklift stuck, and I mean stuck. I will have to pour a slab before I take the forklift there again.

 

[slabmaster]

Today at the tree school on the Umpqua, I was taking a class on the practical science for portable sawmill owners (part 1 milling, part 2 drying) I was talking the man that designed and built the solar kiln for Virginia tec. He told me not to build one with his design because it had too many limitations. To start with, it could only be 8’ wide to fit on a trailer. This also made it hard to load. He told me that Gene Wengert with the University of Wisconsin had designed and built a much better solar kiln.
http://owic.oregonstate.edu/solarkiln/plans.htm
Place your collector at you longitude plus 10. For example I am at 44* longitude so I would place the collector at 54* so that I would collect more heat during the winter months. I am getting everything together to build one using sawdust for insulation and a wood furnace as a back up heat source. That can be loaded with a forklift. The problem that I have is that the best place to build it is where I got my forklift stuck, and I mean stuck. I will have to pour a slab before I take the forklift there again.

Nice post! Should be very helpful to anyone building a kiln.

 

[Nikko]

Good info, thanks Backwoods.

Nikko

 

[Sawyer Rob]

He told me that Gene Wengert with the University of Wisconsin had designed and built a much better solar kiln.

Which is the one Al Weber recomended above...

Mr. Wengert is a very nice guy, i've talked with him and also emailed him. He's full of knowledge and very helpfull...

Rob

 

[Backwoods]

http://owic.oregonstate.edu/solarkiln/plans.htm
Gene Wengert is the go to guy for information on solar drying. His studies of the science of what happens on the cellular level is the basis that everyone else has designed and built there kilns on.

As most of you know the heating and cooling affects of the solar kiln is the ideal conditioning process for drying wood so that it relaxes the tensions with in the wood.

What I found interesting in the class is that moisture is held in the wood two ways. 1. “free water” is held between the cells and is easily released. That is the drop to about 20% moisture content. 2. The rest of the moisture is chemically bound to the cells and not within the cells, as I had been tough. This brings use back to drying that figured Myrtlewood.

 

[RandyinLangley]

Thanks for the info Backwoods. Do you think a combo machine with Solar and DH would work fine without compromising the cell structure? I'm a bit concerned about the winter months and the lack of sunlight. I think in the peak of winter we get about 6 hours of daylight and the themps are around 4*C so a combo machine might be best for the winter time.

There was an article in American Woodworker in 2002 that laid out the plans to build a small Dh kiln, I was thinking or incorporating something along those lines in to a Solar/DH kiln. Go solar in the summer when there are 17 hours of daily (today) and go DH in the winter with aux heat?

Thoughts?

 

[Bushler]

There's actually three ways water is held in wood. Picture the cell structure of wood as being a series of soda straws held togeather with a matrix. The 'straws' have water in them, there's water between them, and there's water in the matrix cells.

The shape of the 'straws' changes from round, to square, (sort of) as the M/C goes below 20% and adds to the ridgity of the wood. It's also why there's more distortion (warp) from 20%>5% then from say, 80%>20%

One word of caution, kiln drying cooks some of the life out of wood. This isn't a concern for most projects, but for boat lumber, musical instrument grade lumber, or for a highly finished cabinet/furniture wood, slow air drying is best.

 

[Brmorgan]

There's actually three ways water is held in wood. Picture the cell structure of wood as being a series of soda straws held togeather with a matrix. The 'straws' have water in them, there's water between them, and there's water in the matrix cells.

The shape of the 'straws' changes from round, to square, (sort of) as the M/C goes below 20% and adds to the ridgity of the wood. It's also why there's more distortion (warp) from 20%>5% then from say, 80%>20%

One word of caution, kiln drying cooks some of the life out of wood. This isn't a concern for most projects, but for boat lumber, musical instrument grade lumber, or for a highly finished cabinet/furniture wood, slow air drying is best.

Yep, "Free water" is contained within the cell cavities, "bound water" is held in the actual fiber of the cell walls. The fiber saturation point (when the wood will not swell any more if more moisture is added) of most north american species is about 23-30% MC. Then there are woods like Subalpine Fir that can have a >100% moisture content.

Kiln drying won't harm the durability of a wood - quite the opposite - but yes, it isn't ideal for wood that will be used in specialty items because conditions such as honeycombing and casehardening occur easily, which are very damaging for the uses you pointed out.

I built myself a mini kiln-box to dry smaller pieces for projects. It's just a 2X2X8 foot plywood box, lined with that insulating foil-covered bubble wrap stuff. I use two or four heat lamps as a heat source, and also have a dehumidifier if I want to dry faster. I also ran a ducting pipe from one end around back to the other end with an inline duct fan to circulate air. With only 2 heatlamps going (no dehumidifier) it will hold at almost 125°F and will pull 2-4% of moisture out of a good sized load per day. I haven't run a full load with 4 lamps and the dehumidifier running yet though. An old woodworker friend I have (actually one of my high school shop teachers) has a similar box but his isn't insulated, and he uses one of those 240V cube shop heaters blowing thru a pipe into the box to heat it. I like mine better though, because I don't need a 240V plug for it, and I have the lights and fans on dimmer switches so the drying power is infinitely variable.

 

[Bushler]

"When the average non-professional has need for wood for boat work, he will all too often make a bee-line for the nearest building supply dealer or lumber yard. What he comes out with is some kiln-dried lumber, whose life has been cooked out in the drying process, whose natural oils have been leached away, and which is naturally receptive to dry rot. Kiln-dried lumber is dead, as compared to with air-dried, and it not suitable for boat use-if you want a first class job."

from, Boat Carpentry, Hervey Garrett Smith

 

[rdb305]

Hoop house

Question: Could you use a hoop house as a kiln?

 

[woodshop]

Tell me what a "hoop" house is...

 

[Backwood]

Tell me what a "hoop" house is...

I would have guessed a place for drying cheese but thats probably not right coming from Miami

 

[irishcountry]

I think he is saying a small semi-circular greenhouse. I am pretty new to the milling game this is my first summer but I have 2 greenhouses that is my business and this summer I put some boards in my smallest in july which is when my spring season is done. It didn't take long in july weather and those boards were very light I don't have a moisture meter but I have no doubt they were pretty close to using them safetly for wood working. Now that said it was red oak that had been down for quite a few years so i'm sure that was a factor but it gets HOT if you don't run the fans all day which I turned them off on purpose. One of the boards warped and cupped badly I was told by a woodmizer owner that its getting the wood down to 20% that is critical before you sick it in the sun to finish he said if you take a green board and stick it in hot dry conditions right away it has more of a chance of warping. Just passing it along not sure if its totally true he did say it can also depend on what type of wood how thick and how its cut (quartersawn ect.) just my 2 cents