# diy kiln for.smaller.slabs



## jimmyjames (Nov 23, 2012)

,Hi, im going to build a.small kiln out of plywood, going to be 24"x72"x24" tall, insulating it with styrofoam on the outside. I plan on using a controller i have for the tempreture, heating will be from some 100 watt light bulbs, i need to dry 4 slabs of maple that are 52x22x1.5", i will also have a small dehumidifier in it, do you guys think this will work? I can accurately control the temp +/- 1 degree, will also have a fan in it to circulate the air around the wood, 2" stickers between the boards. Any thoughts? Temp will be 140, anybody have a time frame on drying time? Reason for this is that no mill has any interest in kilning 4 pieces of wood and id rather not wait a year for it to air dry. Its ambrosia maple bookmatched slabs


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## qbilder (Dec 19, 2010)

It'll work. 140 is pretty warm. Not sure how long it'll take. That depends on moisture content before kilning.


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## Shop Dad (May 3, 2011)

You may want to pick up Daren's kiln plans: http://www.woodworkingtalk.com/f23/small-wood-drying-kiln-plans-dry-your-own-lumber-3103/


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## MidGAOutdoor (Apr 7, 2011)

yes Darrens plans will work. why light bulbs if a DH is used? also why a fan if a DH is used? the DH will circulate the air in im correct. you'll also need to run a drain hose outside for the DH. i just use a 150 watt flood light and a fan and it works for pine and such but im cheap. mine is 4ft long 2 tall and 2 front to back. throw a piece of plywood on top with one end elevated with a sticker and a tarp on top of all that. works well.


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## Da Aardvark (Oct 11, 2012)

140 deg is too warm and will dry things too fast. 130 deg is bug kill and my setup gets it there and further. 
I generally set it at 90 deg and for what you are drying, and maybe 130 for a day if I suspect bugs, but don't stay there for long. Just tarp it over (cheap blue tarp) and put a small under desk space heater (it's dry heat) on one end, blowing the heat through. 
Open the other end for escaping heat/moisture. Reverse direction once a day so one side doesn't dry faster than the other. You can even place the heater on the sides and let it blow out the ends. What wood you have, @ 90 deg., will be dried on the surface in a matter of days. Internal drying will take a week or so, but you gotta do a cut and a check to test.
Sticker the wood and end seal, also seal any knots, splits as best you can.

I've dried many stacks of slabs and hollow logs with just a tarp and a heater.
The beauty is you are not locked into a specific dimension and setup and can change heat directions and configuration at will.

It costs you 1ea. blue tarp, 1ea. $20.oo space heater, 1ea. thermometer, stickers for wood. 
And you need a moisture meter which can be bought at Lowes for less than $50.oo.

On drying wood, generally what I pick up has already had some air dry time stacked and stickered. I get most of my stock with 20-35% moisture content. It's good to allow some air time first to get them somewhat stable. Next I'll lay the heat to them, @80deg or so for a day and work it up to 90-95deg. If I suspect bugs, after a few days I'll kick it up to 130-135deg for a day, and then back it back to 90ish deg and stay there until done.
Usually on walnut slabs with 3 to 5 each, 6ft x 2ft x 2in, I'll have the stack surface dried down to 5-8% within 4 to 5 days, Internal check shows a little higher, like 8-12%. If I see higher than 10% I stick em back in for another day or so.
All woods have their own characteristics and dry times. You just have to check em on occasion.
Also, I deal mainly with live edged wild grains which have a tendency to go nuts. I've bar clamped the stickered wood so it can't move.

Good luck.


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## MidGAOutdoor (Apr 7, 2011)

Aardvark, can u put up a pic of that? thanks


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## jimmyjames (Nov 23, 2012)

Again ive never kilned.wood before. But i dont trust the tarp and space heater method in the garage of my house, so 90 degrees is the temp to hold?


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## scsmith42 (Jan 24, 2011)

Jimmy, I'm a kiln operator. There is a lot more to successfully drying lumber than heat and humidity. Each species has a maximum safe daily drying rate based upon the lumber thickness and initial moisture content. We use kiln schedules that provide guidance regarding temperature and RH% inside the kiln based upon where the lumber is at in the drying process. Typical air flow rates through the lumber stacks are around 350 fps, give or take. 

If you dry your lumber too quickly, you will destroy it's suitability for woodworking projects.

Before going too far down the path of building your kiln, I would suggest that you take the time to learn more about drying hardwood lumber. That will help your initial efforts to be more successful.

Daren's kiln plans are a great place to start. Also, I would suggest that you download an read "Drying Hardwood Lumber" from the USDA Forest Products Lab. Here is a link to it:

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr118.pdf


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## ETWW (Mar 27, 2011)

scsmith42 said:


> Jimmy, I'm a kiln operator. There is a lot more to successfully drying lumber than heat and humidity. Each species has a maximum safe daily drying rate based upon the lumber thickness and initial moisture content. We use kiln schedules that provide guidance regarding temperature and RH% inside the kiln based upon where the lumber is at in the drying process. Typical air flow rates through the lumber stacks are around 350 fps, give or take.
> 
> If you dry your lumber too quickly, you will destroy it's suitability for woodworking projects.
> 
> ...


Excellent advice.


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## Da Aardvark (Oct 11, 2012)

MidGa...
It's just a tarp draped over the stack with a few standoffs to keep the tarp off of the top of the stack.
a pup tent like setup. 
No pix's, sorry.
Jimmyjames
Whats not to trust? The space heater?

Another method is to throw the stack in a hot attic and let the sun do it;s work. What I don't like about that is the variation in temps from night to day.


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## jimmyjames (Nov 23, 2012)

Ok, the planks are not the wet, i was told mid to high teens, i will test when they get here, the wood is soft maple. Can i really screw them up that bad if i kiln them at 90 degrees? I am trying to read up on it but everybody just suggests to pay this guy for drawings of a kiln, i can engineer anything under the sun.... i have autodesk inventor, autocad, solidworks, mastercam, camworks, cambam, inventor fusion.... so i can draw my own drawings, all i need to know is the kiltempreture, if the tempreture needs a certain ramp up/down, a maximum rate of moisture "draw off" and what the targer moisture content needs to be. On a daily basis i heat treat and anneal tool steel that is much more expensive than these slabs of wood and much more crtical with the temp/ramp and soak times.....


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## scsmith42 (Jan 24, 2011)

jimmyjames said:


> Ok, the planks are not the wet, i was told mid to high teens, i will test when they get here, the wood is soft maple. Can i really screw them up that bad if i kiln them at 90 degrees? I am trying to read up on it but everybody just suggests to pay this guy for drawings of a kiln, i can engineer anything under the sun.... i have autodesk inventor, autocad, solidworks, mastercam, camworks, cambam, inventor fusion.... so i can draw my own drawings, all i need to know is the kiltempreture, if the tempreture needs a certain ramp up/down, a maximum rate of moisture "draw off" and what the targer moisture content needs to be. On a daily basis i heat treat and anneal tool steel that is much more expensive than these slabs of wood and much more crtical with the temp/ramp and soak times.....


Let me get this straight.... I post a link to a FREE DOWNLOAD of excellent information about drying lumber (which includes some of the info that you're requesting BTW), and Darren only charges *20 bucks* for his plans, BUT you would rather take the time to draw your own plans.... but not invest the time to learn more about what you're trying to do, or spend a lousy twenty bucks with the guy who freely donates his time to provide this forum for you to use without charge?????

To answer your question, if you take 8/4 green oak lumber, put it in a 90 degree environment and 30% RH, yes you will probably screw it up. If you take 4/4 oak lumber with 18% MC, you probably won't. 

There is no set, single formula for drying lumber. As I stated earlier, the schedule that is used is contingent upon the species, thickness, and initial moisture content of the lumber being dried.


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## Tennessee Tim (Dec 15, 2010)

Daren's plans are excellent and very informative.....BEST MONEY I EVER SPENT concerning wood....He has an example of a small kiln BUT you can change it any way you feel need be...I DID..3 different times (setups) and used the same D/H each time. 

You have to be very careful speed drying with extreme heat.....I don't reccomend it JMO...ALOT of FACTORS to keep up with to prevent damages. Large kilns do use speed, heat, controlled closely AND have to add water back (steam, etc.,etc) to relieve stresses.

Posting pics of the pink kiln and the "Super kiln" I built:blink::laughing::laughing:.....THIS IS EXTREME, TO THE MAX for his basic plan....I didn't design for speed DUE to the volume...but ADing down low helps offset drying time.

There are many variables, arguments, etc. , etc. pertaining to drying correctly and properly. My opinion the "BEST WAY" for wood in my "opinion order" :
1) AD...is natural and relieves the stress the best ..but in most conditions it needs a final few % of MC removed and debugged for indoors in a kiln 
2) Solar Kiln...is faster than AD yet relieves stresses at night as AD does...some designs and areas claim can debug....but I like 48 hrs at 130+ for my satisfication. 
3) Small D/H unit as Daren's plans....doesn't use high heat, good moisture removal, doesn't stress the wood and if setup correctly (I undersized one attempt on the "super kiln")can debug.
4) Large commercial kiln...have to normally destress due to speed.

Lots to obsorb.:blink::huh::yes::yes:.

Have a Blessed and prosperous day in Jesus's Awesome Love,
Tim


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## Da Aardvark (Oct 11, 2012)

My system/method is makeshift and i won't make claims of it being the best or the best practice for drying wood. 
I do have a percentage of loss when it is done like I do.
But that percentage has been low. and considering the lack of expense I have in the setup and the ability to wrap up a tarp and throw it on a shelf (space savings which here is of premium value) the losses are a calculated risk and financially I'm ahead of the game. I could buy a lot of slabbed wood for the costs of a kiln, and again, space here is a premium. I cannot take up an area long term, just for wood drying. Kiln space to me is shop space lost. A non starter. 

I've dried 1 1/2" - 4" thick hollow logs 3 ft across, 3ft long, maple, in my tarp kiln. There was a loss due to cracking of about 20% and their original moisture content was up around 40% I got em down to 5-10% moisture in 4 weeks. The thinner ones came out faster. Temps were @90f and a 130f stint for bug kill. The loss was expected, especially since they are end grain. pieces.

On slab wood, like you are doing and (as mentioned above), I've lost none of them in walnut, but they were nowhere near as wet to start with.

I will concede my methods are crude, but they have done exactly what I wanted and expected, actually better than I expected.
If you want to be more precise, I suggest the info posted on wood species and drying time/heat methods. I don't need that precision.


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## Chris Curl (Jan 1, 2013)

i am doing a small project where i want a couple of pieces of limbs. so i found a tree that had fallen and cut a couple of pieces in the sizes i wanted. 

i have no idea what kind of tree it is, how long ago the tree fell, or how dry the wood is. 

following the info from this thread, to have a better chance of it being dry, would it be a good idea to enclose it as described in my unheated garage and have a fan with a heater or light bulb to provide some warmth?

or would it be pretty much as good to simply store it in the house for a couple of weeks before using it? there is no humidifier in the house.


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## Da Aardvark (Oct 11, 2012)

Ya gotta get it down to 10% or less m.c. to be usable for furniture and not shrink up on you later.
If it's small, and you don't care about cracking, throw it in your household oven for a few days at less than 200 deg...(yer wife will have a fit, but)...


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## Chris Curl (Jan 1, 2013)

it's not for furniture; it's for a mallet. from a drying perspective, i guess it would be better to take the bark off?

i am planning on drilling a recess into it for the handle. would it be more likely to crack if i drilled it and then put it near a lightbulb/fan for drying. i imagine it would dry faster (if it is even that wet - who knows? i don't have a moisture meter)


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## Da Aardvark (Oct 11, 2012)

Well my method is a little unorthodox, as many would say.
I use a blue tarp and a under desk sized small space heater. So when I'm done it can all be rolled up and put away in a small space.
I pup tent over my wood and seal the ends loosly so air can blow through a little, and put the space heater on one end. On large pieces I move the space heater from one side to the other, ever day or twice a day. I keep temps at about 90deg, and a 1 day blast of 130deg for any suspected bugs.
A moisture meter can be bought at Lowes for ~$40.oo.
A old method of moisture check is to put the end of wood up to your lips. Your lips will notice/sense moisture. Its a method I use camping to see if wood will burn.

Wood drying is a process much discussed here if you search it out. Not dry enough, it will move and shrink on you later.


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## HomeBody (Nov 24, 2010)

jimmyjames said:


> ,, heating will be from some 100 watt light bulbs,


You have another problem. Obama banned the 100 watt bulbs.:thumbdown: Gary


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## Da Aardvark (Oct 11, 2012)

HA!
Yeah, there like gold now.


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## Chris Curl (Jan 1, 2013)

HomeBody said:


> You have another problem. Obama banned the 100 watt bulbs.:thumbdown: Gary


i'm a die hard conservative, and was 100% against it. i have a huge case of them in my garage. 100 4-packs

didn't they also just phase out 75w bulbs too?

i'm sure barry was all for it, but he can't be blamed for this one.

actually, the democratic congress passed the bill while bush was the pres, and bush signed it. 

even though he was a republican, bush was a big spender and not a conservative


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## Chris Curl (Jan 1, 2013)

thanks da. for a cut limb like mine, about 6" in diameter, about how long would you give it the pup tent/heater treatment?


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## Da Aardvark (Oct 11, 2012)

Probably a few weeks.
Seal the ends.


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## Chris Curl (Jan 1, 2013)

Da Aardvark said:


> Probably a few weeks.
> Seal the ends.


sorry, do you mean seal the ends now, or in a few weeks after it dries?

and what should i seal the ends with? my inexperience is showing, i know.

thanks


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## Da Aardvark (Oct 11, 2012)

As soon as you cut it, you should seal the ends.
So, yes, Now! It lessens end cracking.
I use clear latex paint but again, I'm uncommon in my processes. Most use Anchorseal
It's also easier getting the bark off when wet.

No matter what you do, you will likely see a few checks or splits
.........
Also a diehard conservative Libertarian here.
I won't ever use GE's mercury filled bulbs. They are now (amongst other things) being cited for eye damage.


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## jimmyjames (Nov 23, 2012)

well i built the kiln, ran it for 16 days, slabs started out at 3" thick, had them resawn into 1.5" thick slabs, the exposed cut(center of 3" slab) read 15% moisture , i started the kiln at 90 degrees and raised temp 3 degrees per day and last night ramped it to 130 and held it there until this afternoon. Anywhere on the slabs i cannot get a reading above 6% and thats driving the pins in completely. The slabs are still stacked and stickered in the kiln but with everything off, i will let them sit and stabilize for a while before working them. For heat i just ended up using one of those small desk top space heaters and worked like a charm, on a few days the dehumidifier produced enough heat to keep it to temp but when the weather outside was 10 degrees the space heater kicked on to keep the temp up. Also my dehumidifier's water output drastically reduced after about 7 days, for the last 9 days the output was maybe a total of 1 cup of water, i think the water was evaporating out of the collection container faster than it was producing. The ends of the slabs did not check and i see no signs of warping when removing the clamps i used to hold them down, all of them stayed flat but i did put the clamps back on while i wait for them to stabilize.


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## Da Aardvark (Oct 11, 2012)

Yeah, it's like that.
When we aren't drying them in a totally professional manner we go as we go.
Sure errors are made and i have a ~20% loss of product that must be used for other purposes other than planned.
Generally though, on even walnut I'm only paying ~$1.25-$1.50 a bd ft, and at that price, some loss is fine. 

I've also clamped a stack of stickered slabs together more than once and it holds them somewhat stable. Any warping/cupping I've had so far was removed by a planer. I've had to remove upwards to 1/2" on a few boards, which was somewhat expected prior.

Overall I rarely have more than 5 large slabs at any one time under the tarp and heated. It's for the next projects and I dry them as needed. 
So an expensive setup for drying is nonsensical for me and to buy them already kilned is not cost effective. I also don't have the space for a solid setup here.
We do as needed. It might be on the fly and not conventional but so be it.
My go to supplier for wood has wood stacked in his garage attic with the sun warming his wod, as a slow drying technique... It works fine.


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## ETWW (Mar 27, 2011)

The science of drying lumber was worked out decades ago...kiln schedules, safe drying rates, etc. By adhering to those tried & true methods, defects from improper drying can be reduced to a miniscule percentage of the total product. There are no shortcuts or re-inventing of the wheel that will assure a quality end product although sometimes we get lucky.

A 20% loss in product due to drying degrade would bankrupt a commercial operation pretty quickly. For us small-timers, it's mostly an annoyance. It means that when drying five slabs, one of them is checked, cracked or warped. The other four are acceptable. That is deemed success. For a large operation, it would mean that 10,000 bf out of 50,000 bf was made into firewood. That is a financial catastrophe.

I have a hard copy of that publication scsmith linked to...Drying Hardwood Lumber. Even for those of us who use unorthodox drying methods (thanks Aardvark) it is worthwhile to read and absorb the information contained in that publication. It's factual, it's proven and it's a worthwhile read for those of us who love working with wood.


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## Da Aardvark (Oct 11, 2012)

ETWW
There is a place for what you mention and most fine furniture/cabinet shops will adhere to what you are pointing out.
I've reviewed the literature you mention and agree with the sciences of it, and your points. If I had a big operation and was concerned bout my losses vs the cost paid for product, it would be important to me. Seeing that I pay a very low bd.ft. cost for unique premium cuts, I'll chance some losses. When I say for my purposes I have a 20% loss, it just means the wood won't be suitable to be used for what I intended. It will be used for other purposes, so in essence it's not a total loss.

To me personally, the biggest loss is loss of workspace due to wood being stacked everywhere or having floor space set aside for a proper kiln setup. Shop square footage is of a premium to me.
I can't keep lumber around and let some of it air dry to a point before kilning it. Someone else must do that for me.

The wood supplier I use has a practice of air drying to a point, before he sends his stock off to a kiln. A good practice. I buy from him between the time the tree has been slabbed and he sends the wood to the kiln. I do that so I get first dibs on the wildest grains, and I get it before anyone else sees it. Thus I take my chances, and kiln my own piecemeal. I generally get my stock between 20-30% m.c., and then I allow for a few weeks of drying in a makeshift kiln.

Also, in general the rules of drying for my projects don't apply well. I do primarily wild twisted grained woods with live edge or bark on, bug chewed, and infested damaged furniture pieces. Due to the nature of the type of pieces I use, most cutters would discard what i mess with, and send them to the burn pile (again a cost savings). I do on occasion buy pieces from my supplier but that is the exception rather than the rule.
Nothing I have done to date is conventional 'Norm Abrams' straight grained, fine joinery. It is the dregs, re-habbed, and brought to life. Rules don't apply well.

I can give an example where a known 30% loss was going to be realized. I found a stockpile of hollow shagbark maple logs with diameters upwards to 6ft and side thicknesses upwards to 8". I took home 30ft running length of hollows measuring 42" dia, down to 30", and side thicknesses varied from 4" down to 1.5". They were drastically bug chewed, and black ants were scattering like a bomb went off. Skin m/c, varied from 20-45% after the wood was debarked. I cut them to a little over table height (kitchen/coffee), and stacked them in a smokestack fashion for kiln drying, tarped em and let the heat fly. Some were done in a week, and some took 2.5 months.I had 10 pieces when the stacks were set up.
I lost 3 of them due to the extremes I put them up against. 2 of them split length wise all the way through. 
But no piece was wasted. What I couldn't use as a table was cut up into other pieces and legs. 
These pieces cost me nothing except the chainsaw and trucking time. $150.oo. I've made 5 finished projects from them so far, and have 2 left. The others were given away and a few small chunks hit the fireplace..

My point being,
Rules don't always apply but are good guidelines. I'm not trying to tell others to circumvent the rules, but I am saying there are times when rules won't work for them, and they need to distinguish wether they have the funds/space/need for all the specialty equipment many would push on them.
For me it's the logic of money for certain equipment, or not, and floor space for all the expensive tools that likely will rarely be used.


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## scsmith42 (Jan 24, 2011)

I think that many of the responses miss the point. 

The fact of the matter is that when you dry lumber well in excess of it's recommended drying rate (based upon species, thickness and initial moisture content), in terms of traditional woodworking projects you're damaging the wood. This is especially true on thick slabs. So let's quit arguing that point.

The real issue is that some of you are building projects from your lumber where case hardening, internal checking, etc is acceptable and is not considered to be a detracting factor. Therefore, you are obtaining a result that is fast, effective and inexpensive for your specific needs. I see nothing wrong with that. 

What I do object to is when misinformation is presented to other woodworkers who may read this thread and think that they will have success in drying lumber for their furniture projects by following methods that dry at an excessive rate for the species, MC% and thickness of lumber being dried.

One fact that has not been mentioned is that most species of wood, once they are below 25% MC, can safely be dried at a faster rate. Da Aardvark, I think that since your lumber is already significantly air dried before you put it in your "kiln", this is one reason why you have been achieving your results.

The focus that Darren, myself and others have is on drying lumber w/o damaging it in any way. For us, providing a high quality product to the end user is our primary need; case hardened and honeycombed lumber is not an acceptable outcome.


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## Da Aardvark (Oct 11, 2012)

scsmith
Agree that the <25% m.c. has a bearing on the success of my projects drying without cracking/splitting/etc. At the same time, however I've had success with wetter wood as well, but the concept of air drying to the <25% m.c. has much merit.
My intent is not to mislead and I've made it clear that the poster wood will likely show signs of cracking/etc. It's a chance that he will take.
My intent is to aid those who don't have the resources and access to fancy or expensive equipment or kilns, and when drying 1 to 2 boards every now and then, the question is what to do? I'm giving a cheap solution with consequences, but it's kept my operation in wood for a year now with 13 furniture projects finished and without too much loss or problems, and it all be packed up in a 12" x 12" x 12" area and stored until needed again. Cost is also minimal.
Is it the best way? Not at all! It's just an option.
Is the drying speed excessive? At 90deg F, I say no.
Mind you (as stated) I don't do fine joinery or use straight grained woods but I want the grains to show in a pristine manner, or they are rejected.
Also in some of my projects the cracking is emphasized, but that is thought out before ever starting up.


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