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Baron
Baron's picture
Slab drying

I've heard it said or suggested that thick slabs need to air dry for a long long time and then they will also need a long time in a kiln to draw them down to 6 or 8%  make them safe to use. I'm trying to collect some Tabletops and Gun Stocks. Some are 2" and some are 3". Why can't they just go in the kiln right away? What issues would I face?

Baron

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r.garrison1
r.garrison1's picture

I've read a bit about what violon makers look for in wood, and how they despise kiln-dried wood, so I have some thoughts. I don't know it is supported by fact, however.

As the wood dries, it kind of stabilizes for the new moisture level; the cells kind of adapt to their new environment. When kiln dried, this adjustment doesn't go as planned, and there is some unresolved tention or something left at the cell level; not necessarily organized enough to pull the wod around and cause warpage, but an overall instabillity. The wood doesn't 'sound' right, no matter what you do.

 

I don't know if this would even translate to what you want to do; you really don't care how a gun stock sounds...

Baron
Baron's picture

No but that explains why my violin lessons are going so poorly. 

 

eddiemac
eddiemac's picture

Many lumber species can go direct to kiln.  Oak is one of the most problematic, so is often air-dried for a few months first.  The thicker your slabs, the longer the drying time, kiln or not.  "Sawmill & Woodlot" published a tree species series in their magazines covering most of the kinds of logs we get in North America.  Each one detailed how easy it was to saw, machine, and dry the lumber and how to do it   ---   very well done.  I think they still sell the series on-line.

Baron
Baron's picture

Thanks Eddie. I'll look Into it. 

Post Oakie
Post Oakie's picture

The #1 reason wood doesn't go straight into a kiln off the sawmill is because it costs more.  Straight off the mill would take 4/4 oak a month in the kiln, while air dry lumber can be ready in a couple of weeks.  So you can run twice as much wood through the kiln if it is air dry first.  Lots of defects occur by pushing the wood too hard, all caused by the fact that wood shrinks as it dries.  Push the drying too fast, and the wood on the outside is so much drier than the wood on the inside that it either cracks, develops tension (case hardening) or squeezes the wood on the inside enough to crush the cells (honeycomb).  Air drying lets the wood dry slowly enough that you don't get so much moisture gradient between the inner wood and outer wood, though you can still damage the wood in a kiln if you push it too hard.  A number of textbooks have been written on the subject, and there are courses available on drying wood-- it's that complicated.

You don't care how a gun stock sounds, but you DO care if it develops cracks!  Typically a gun stock blank needs to air cure for at least 3 years before being finished off in a kiln.  Right now, the #1 thing to do is to end coat the logs or boards to avoid end cracks.  I use AnchorSeal, but a lot of people use several coats of latex paints.  If you search this forum by the key words "end seal" you'll get more info.

A couple of good books on the subject are "Understanding Wood" by Bruce Hoadley (this is THE definitive reference on wood), and "Wood and How to Dry It" by Fine Woodworking.  Both are available on Amazon.com.

Baron
Baron's picture

I have Hoadley's book and am about a quarter of the way through. I'll look for the other. 

 

What type of Kiln do you plan to install? DH, steam, other? It is bugging me that I can't get behind the solar thing but it just doesn't seem practical for my needs, not in PA.

Post Oakie
Post Oakie's picture

Planning on solar with a wood boiler for backup... if I can scrounge up enough firewood to fuel it smiley.

Baron
Baron's picture

That sounds fun Postie. Will you be able to control temp from going up too fast. I've no experience with it but rather have read about it being necessary to raise temps slowly for certain species. Gene W. wrote somewhere to the effect that one of the big advantages of the solar kiln is that it lets the wood fibers relax somewhat at night and get re-stabilized. I've wondered though, with a hybrid system like the one you propose, if you should or shouldn't try to simulate those same temp swings when using the boiler alone......in other words cut it back at night?

Will you use an electric dehumidifier in addition to vents or haven't you gotten that far with your planning yet?

Post Oakie
Post Oakie's picture

I'm going to start out without a dehumidifier, but have the option open to add one if it looks feasible.  As I understand it, electric heat is the major consumer of energy for a dehumidification kiln.  Eliminating electric heat will let me use 40 amp service instead of 200 amp service.  We'll see.  Straight solar for now.

Baron
Baron's picture

I'm sure it will be fun to practise what you've read about for years and I'm sure you'll provide us with updates when the day comes. 

Baron
Baron's picture

I'm sure it will be fun to practise what you've read about for years and I'm sure you'll provide us with updates when the day comes. 

Baron
Baron's picture

The recent sale of some slabs made it possible to purchase a 48' trailer this past weekend. I hope to put a Kiln into it before winter. I want to have the ability to handle 12'. I'm wondering how long to make it? 12', 12.5', 13'?

I'm beginning the process of collecting supplies.

At the show a vendor, nope not Postie, spent allot of time drilling into me the importance of Anchorseal and or other end coatings. Has anyone sprayed Anchorseal?

smithbr
smithbr's picture

If you're loading mechanically, not by hand, leave a bit of room for the operator to miss the ends of the opening!  Also, logs are often roughcut 4-8" overlength.  Unless you want to trim your boards before loading into the kiln,  you'll want a bit of room.  Thirdly, a bit of space for air circulation is good.  Lastly, don't know about you but even if all my lumber were the same length, by the time I stacked it at the end of a day like today (34 celcius in the shade), it sure as heck wouldn't be straight.

just my 2 cents (canadian, worth about 1.35 right now)

Baron
Baron's picture

We don't have any  celsius's floating around down here. But I appreciate your experience. I'm thinking either 14 or 16 feet. 

r.garrison1
r.garrison1's picture

One thing I would think about for dehumidification is borrowed from another farm industry.

My wife is from Apple country, and they had a lot of Apple drying sheds in her neck of the woods. They all had a cupola to help draw off the moisture.

Not sure how that would apply, but maybe design the kiln to allow the moist air to excape better.

 

Here's a link on apple drying sheds

http://naldc.nal.usda.gov/download/ORC00000100/PDF

 

 

Baron
Baron's picture

That is a cool link. I can imagine how good it must smell to be in the area of apple drying houses

r.garrison1
r.garrison1's picture

My favorite is when I visit the family farm, I pick up some dried apples (and pears).

They dry them until they are crunchy; not leaving residual moisture.

I crumble them over oatmeal for breakfast; love it!

Post Oakie
Post Oakie's picture

Terrific link.  I never realized how many similarities there are between wood & apples!   A little sawdust on your oatmeal will add even more fiber to your diet.

ScottS
ScottS's picture

Anyone thought about solar heat in a solar kiln?

http://www.builditsolar.com/Experimental/PopCanVsScreen/PopCanVsScreen.htm

 

I'm Kicking around that idea especially to keep the kiln more active in the winter. But first I need to build the kiln:)

Post Oakie
Post Oakie's picture

EddieMac is our expert on solar kilns.  I believe his is based on the Virginia Tech design.  http://www.solarkilninfo.com/solar-kiln-resources-on-the-internet/links-to-plans-for-building-a-solar-kiln

I've got one started, based on a shipping container.

eddiemac
eddiemac's picture

I am an expert on my solar kiln (as described in the solar kiln thread here).  Beyond that, I yield to others.  Anyone who wants to see the kiln in person or wants to ask questions is welcome, but my experience is limited to the Virginia Tech model that I copied.  I have a feeling Oakie could be a great resource for information on the subject and I look forward to his input concerning what he is building for his own operation (especially the supplemental heat aspect).

ScottS
ScottS's picture

Yes I too will base mine on the Virginia tech plans but maybe a little wider. The guy that mentioned the solar heater uses his in a Virginia tech kiln but uses it for firewood. He can crank up the heat and dry green firewood fast because cracking is not a issue. He also built one to heat his garage in the winter. I plan to use a window screen heater shown in the link above to help get better temps in the winter. Cause by the time I get around to the kiln after my mills done and had a roof over it, It will be winter.

 

So EDDIEMAC HAVING OPERATED YOURS FOR the last 2 or 3 years (based on your thread I have read a 20 or more times) is there anything you would do different? And did you do 2 roof covers on top of  each other?

  And also in that thread you state you couldn't bring yourself to build it with cedar. Why??? I saw were cedar is harder than most pine and fir (what most 2x4 are around here). I plan to use cedar a lot. Wait for my 24' clearspan cedar maybe cedar and pine gluelam thread coming soon after the mills built. They simple want too much at the hardware store for gluelams and I joist, and a steel I beams way too much. I know I can make my own and it will work.

Baron
Baron's picture

I'm jealous. I cAnt imagine having enough cedar to through it away like that. A 6 or eight foot x one foot is big for my area. 

eddiemac
eddiemac's picture

Scott, you caught me on the cedar.  To people in other parts of the country, eastern red cedar is somewhat exotic.  In southern Missouri, Arkansas, and Oklahoma, it's almost a weed.  Still, it sells well.  To be honest, the reason I didn't build with it is because I hadn't planned ahead and cut 2 X's out of the cedar I had.  It would have worked well.  I don't think it's very strong though   -  be careful with cedar beams.

My kiln only has one layer of glazing  -  I understand two is best for maintaining heat, but that stuff gets expensive.  Plastic sheeting would probably work on the inside though.  If I did it over, I'd put in a little side door for quick access on small jobs like starting plants, drying vegetables, drying short lumber pieces for projects.  I would have three hinges per side on the big doors and put a little more thought into door construction.  The kiln is by design a big collector, so I wondered how your screen/can collector could augment its heat potential.  If it can, I will definitely try it.  I like to be able to rise to bug-killing temps at the end of the kiln cycle, but can't now unless it's really hot outside.  So I have thought about ways to add some heat.

ScottS
ScottS's picture

eddiemac I have the screen solar heater design in my head. On the link they pull air threw it with a little inline duct fan. I would simple duct it into the fresh air intakes of the kiln Or its own port in the kiln. theses are just thoughts . do you know your average temp in yours in the summer? I have I think a bunch of trial and error coming my way in my kiln ideas but I think a solar heater can help. Or maybe make the whole roof layers of screen before the clear roof material. this would give it a lot more black colored material to heat up and correct me if I'm wrong but doesn't the kiln work like that its heat gain by the black color under the roof not sun on your boards. So the more square ft of material your heating should be more heat you have collected?

 

Boy  you have me thinking now. almost hurts a little.

Cedar is the first thing the people and farmers clear from the fields around here and normally the just burn it. I build beds from it but would die for some aspen around here. but no go period on that.

 

Scott

eddiemac
eddiemac's picture

In my kiln, the sun shines through the glazing and lands on 4 sheets of tin on top of the lumber that are painted flat black. walls that are coated with black tar, and a black vertically rising tarp.  Everything is black.  If you could close off all the upper inlets (and door leaks) and inject some super-heated air coming from an outside collector, I suppose you could raise the temperature.  Plan accordingly.

My highest temperatures last week when the outside temps were around 95 degrees (farenheit) were around 136 at the back of the lumber pile (and ten degrees higher in the upper reaches of the kiln).  When it is cooler, the temps are lower.  Don't know the average.

ScottS
ScottS's picture

Well unless I order a truck load of aspen from Colorado. But I don't have the cash flow for that right now.

ScottS
ScottS's picture

Ok for bug kill where do I need to be. I have it in my head that I can reach 150F easily on first concept in my head. But that would be a day time temp and at night keep circulating that temp with vents closed and depending on Insulation/leaks/Outside temp there would be a loss at night. And off course rainy sunless days. Best of all that would be bring 85F air into the collector. Now if it was on timers this could closed the fresh air once the collectors heated up and keep blowing 150F air over the collector. But what I have no idea on if that would heat the collector higher and if temps could rise above that.

 Sounds complicated but wouldn't be all that hard. It basically would give more sq. foot of heating area. Because the collector can work, I think,  more efficiently and supplement that into the kiln.

 

Btw I hold not phd that say I know anything about my writings of claims.

 

Scott

eddiemac
eddiemac's picture

OK, first let me say powder post beetles are what we need to kill as they are the most problematic and hardest to get to.  When they die in the kiln, everything else is most likely long gone.  The important number for them is 133 degrees.  However there is more to it than that  -  that's the temp that needs to be thoroughly reached inside the wood for about an hour.  To do that, the kiln probably needs to hold a higher temperature for several hours (some say 140 for four or more hours on 4/4, others more or less; thicker lumber takes longer).  I like to take the reading about 18" off the floor, directly behind the stack.  One can get much higher readings at higher and more forward locations in the kiln, but I'm guessing behind is the best indicator of what it might be inside all the lumber.  I have emphasized killing bugs at the end of the kiln cycle because that's when the highest temperatures can be reached  -  moist air doesn't get as warm as dry, and that's when the vents are almost closed.  Vents must be open at earlier points in the cycle to allow moisture to escape.  The advantage of my type of kiln, outside of operating cost, is that it is simple to manage and yields good results due to the fact that every night the wood relaxes (fans off, no heat source), therefore eliminating many of the problems brought on by enhanced drying techniques.

Many species are not impacted by powder post beetles, so they likely don't need as high of temperatures.  The worms in red cedar would be something I imagine to be easier to kill, with the lumber put into the kiln soon after sawing.  My phd is a post hole digger.

ScottS
ScottS's picture

  I have had experience with the worms in cedar. 8 years ago the spar urethane that would get from PPG in Branson would draw the little buggers out on the first coat. I assumed it was cutting off air at the time. Now the government regulated crap in the same brand from PPG wont bring them out. In some logs it takes 2 weeks to notice but you will see little bit of sawdust stuck on a ledge of the carving of a little pile on the floor next to the log. If you look close you will see the hole in in and can jam a rod down there usually and get it. My wife is in love off the idea of a kiln. The thinks is a ok for her to buy green logs to cut in a months time.lol. I told her maybe best for me to line up her logs like I have done for years. To much time in patching carving for what you can charge.

 

As far as the kiln. If the website was correct on there screen solar heater it  was turning 85F air into 150+f. do you think it would make sense to instead build the whole roof into a screen solar heater instead of relying on the sun to heat the black in the kiln?

Too funny I couldn't be happier with my 3pt post hole digger except after hanging on it for down force I feel like I went to the rode

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