Man, you're kiln'n me!!

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ScribbleSticks

ScribbleSticks

Member
Joined
Sep 14, 2007
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334
Location
Nampa, ID, USA.
I read somewhere about someone using a laboratory oven as a kiln to dry some bowl blanks or 2" x 2" x 12" stock or something bigger than what I needed. I thought maybe I could do the same with my green wood billets I have purchased from various vendors.

OK, so I got all hot and bothered about being able to kiln dry my own pen planks and started prowling around eBay for a used lab oven. Man, there are HUNDREDS of them out there; everywhere from $15,000 computer controlled mega-ovens down to the rusty, old, beat-up (but still working :D) Napco 5510 Laboratory Oven I picked for $85 plus shipping.

Next, I go to the 'wood vault' (the cabinet where I store all the wood billets I'm storing for that 'special project') and grab one of the 6" x 6" x 2" tulipwood bowl blanks I picked up at Woodcraft during their last sale. Over to the band saw we head and in minutes, I have a handful of very damp 7/8" square x 6" long pen blanks that need to be dried.

Now, at this point you most likely have figured out that I'm one of those impulsive guys who only read the instructions AFTER realizing that he hasn't a clue what he is doing.

Over to the computer I go to look up the kiln schedule for tulipwood. Ok, there it is and I want 4/4 stock and ....... what the H--L do all these numbers mean?!!!?

OK, now this is where you guys come in!!

This oven cooks from ambient temp up to 250 degrees C. (which according to my calculator is pretty close to REALLY HOT!)

So, how do I do this? I'm sure there's a really scientific way where I get my moisture meter out and check the moisture content of a representative sample on an hourly basis or something like that, but isn't there an Idiot's_Guide_to_Drying_Pen_Blanks_in_a_Cheap_Kiln.pdf out there somewhere?

Isn't there at least one of you rocket surgeons out there that can tell me to "Put it on xx degrees F. for n-number of hours/days then turn it up/down to xx degrees F. for n-number of hours/day, etc.?

I sure hope so, and if you've waded through this rambling diatribe and arrived at this point without saying to yourself, "Man, what an idiot!" then BLESS YOU!!!

Thanks,

Tom aka ScribbleSticks
 
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Hey Tom, you could have used an old microwave or a toaster grill. Also you need to cut your blanks larger to allow for shrinkage and possibly warp with some woods. I would say get the oven hot, put the blanks in for a couple of minutes, take them out, let them cool down, and it will/might need another few minutes, only you can tell. One thing you should consider doing is weighing the blanks, or just 2-3. You should notice a weight change as they become more dry. I think you just blew $85 you could have spent on more blanks. I picked up one of the huge old microwaves from the side of the road displaying a 'free' sign.
 
Ruth is right, when I'm dealing with wet wood, I just chuck up to six blanks in the sacrificial microwave and set it on high for 30 seconds. I wrap each couple pieces in a paper towel to absorb the steam as it comes out. Once they're hot, pull 'em out of the microwave and set them aside to dry to do another batch. I save the paper towels from each batch and let them dry out so I can use them again

As long as you don't 'smoke' the blanks in there, this works great! Between microwave passes, I 'Boy Scout Fire' stack the blanks in front of a little space heater I have for the occasion and let them dry for about 15 minutes, and then return them to the microwave for another pass. After 6-8 trips like this, you'll notice that when you put them in the microwave the paper towels don't get damp anymore, at which point the blanks are turnable.

I also keep a cheapo toaster oven around for slow cooking, but I rarely use it.

I bet your lab oven looks really cool though! Keep us posted if you find some really cool scientific numbers to use!

Like Ruth said, when you rough cut the wood, make sure you allow about an eighth of an inch for warping and such. :)[:p]
 
Ruth and Karl - Thanks for your input on microwaving. I guess I should have been a little clearer. The tulipwood example was just for a test run. I have about 85 bf of various domestic and exotic woods that I will be drying in species specific batches of 50 to 120 blanks per kiln run(stacked and stickered). I realize that there is no one magic time/temperature setting that will work for all species. Basically, I am going to use the tulipwood as a starting point and extrapolate from there based on density and MC. I was attempting to be 'light hearted’ in my original post, but I think I may have come across as being too 'light HEADED' instead of 'light HEARTED'. Any assistance in actually using the KILN method would be greatly appreciated. Please continue to post other methods that may interest those who may be considering alternate drying methods. Thanks again for your input!
 
Not too long ago, I read a thread where someone described his method using a lab oven. I'll try to find it, but me and the search feature don't always get along.
 
I have read where they put blanks in oven at 150 degrees F and check them with a moisture meter about 3 or 4 hour intervals. I use a microwave about as was said.
Bob
 
How do you plan on controlling humidity? I believe most commercial kilns inject steam at certain points during the process to keep the wood from cracking. This is especially critical the thicker the blanks are.
 
Mudder - Good point! I probably won't be able to inject steam, but if I put a small can full of water (like a juice can) in the oven, I think I could at least raise the humidity some. Maybe I could pipe a small electric tea kettle into the side of the oven to 'inject' some steam; just thinking out loud, as it were.

Loglugger Bob â€" Thanks for the temp reference (and in Fahrenheit even!!)

Here are a couple of pictures of what the oven looked like when I received it. I have since cleaned it up a little bit and fabricated a couple of metal shelves for it.
200822718465_napco1.jpg



2008227184636_napco2.jpg
 
hey tom, i'd definitely start at a low temp, maybe that 150 and then keep weighing them until they reach equilibrium. i think the steam injector is a great idea, the can of water might work, that's what a lot of home bread bakers do to keep steam in the oven while baking the bread...
 
Maybe I'm just in the wrong ballpark and don't understand, but with the temp that high,when the wood begins to heat up, won't the water coming out of the wood cause more moisture content in the oven than you would want, meaning you would need a way to get rid of the moisture and not inject more..??
 
I love it when we get back to science or math!

The chief difficulty in the drying wood is the tendency of the outer layers to dry out faster than the inner layers. If these outer layers dry too much while the interior is still saturated, stresses are set up because the shrinkage of the outer layers is restricted by the wet interior. Splits and cracks occur if the stress across the grain exceed the strength across the grain.

The successful control of drying consists in maintaining a balance between the rate of evaporation of moisture from the surface and the rate of outward movement of moisture from the interior of the wood. Therefore, large kiln drying operations monitor the internal and external moisture content of the wood, and when the relative humidity or the kiln falls below parameters where cracking is likely to occur, they inject steam.

Simple, huh? [8D]
 
Lous,

I love the science too! I think your commetns show why the microwave would be a preferrable (although not necessarily practical) way of drying wood. Microwaves heat all the way through, not from the surface in. If a microwave kiln could be built that's big enough to handle all that big stock, I bet they wouldn't need to inject steam. I bet the drying would be more even all throughout the wood.

Julia
 
Why not try Steve Russell's method when he boils the wood? Believe it or not this process works miracles on bowl blanks. I use the boiling method all the time and have yet to be disappointed even one time. I can take a green bowl blank, boil it as per the instructions, allow it to air dry for a day or so (slowly using a paper grocery bag), and then turn like crazy. No problems with splitting, checking, cracking ... nothing!

Go here and read his article: http://www.woodturningvideosplus.com/boiling-green-wood.html

Be sure and visit the home page for more interesting and informative reading. You will NOT be disappointed in what you will learn.! http://www.woodturningvideosplus.com/index.html
 
Steve Russells method of boiling wood has worked well for me, too. I have only tried it boiling bowl blanks and never have tried boiling pen blanks. When boiling bowl blanks I did notice a bit more warping than what he talks about, but have never had a bowl blank crack..yet.

Lou, I understand what you are saying, and agree, but aren't you talking about the 'professional' type kiln dryers? I just know that I took an old freezer a few years ago, put a light bulb in, drilled a hole in top, and a fan in the bottom. The fan wasn't large enough to move out all the air, and the holes in top weren't big enough, so the moisture in the box allowed things to grow that I was never able to identify. I just thought that oven looked like an enclosed box (like my freezer) and was wondering if you wouldn't want to get rid of that moisture. But maybe the oven is different and the temps will cause all the moisture to go away..??
 
John - It's evidently the "control" that is the determining factor. Too much moisture and you WILL grow creatures that look like they were extras in the movie "Alien". Too little and you risk checking and cracking. I'm certain that someone like the US Department of Agriculture will have published stucies that will give a much more precise and correct reply than mine. BTW, significant air movement is essential.
 
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