drying thick slabs

[copperhead10]

first I am new to the forum. I am the owner of a 10" peterson mill and slobber. I am the new owner or a Nyle L200M kiln set up in a 40" shipping container. my goal is to cut and dry 3"-4" thick slabs. With the Nyle kiln can you put fresh sawed oak mixed with oak and hickory that has been sawed for 6 months?

[scsmith42]

Copperhead, welcome to the forum!  This is the best place on the web for information regarding milling and drying lumber.

Congrats on your new Peterson and slabber, as well as your kiln.  It sounds like you have the exact same setup as me, except my kiln chamber is 45' long instead of 40'.

The best advice that I can give to you is to sign up for a Kiln operators course.  Gene Wengert can advise you when the next one is, but they are usually in Memphis, TN.

Rule #1 for kilns is do not mix different species in the same load.
Rule #2 for kilns is do not mix different thicknesses in the same load.
Rule #3 for kilns is do not mix different moisture content %'s in the same load.

These rules can "sometimes" be bypassed if the lumber going into the kiln is less than 25%MC.  In other words, if you air dry lumber for many months until it is below 25%, you can sometimes safely mix species, etc in the same kiln load (but it's still not advisable).

In general, for every inch of additional thickness beyond 1", the drying rate is reduced by 60%.  Thus, if 4/4 green oak has a targeted daily drying rate of 3.2%, then 8/4 green oak is 1.28,  12/4 is about 1/2% per day and 16/4 is around 2/10% per day..

At .2$ per day, a 4" thick, freshly sawn oak slab will need to be in a DH kiln for upwards of a year (and that's with modifications made to the kiln in order to increase the RH% for the first several months.

If you dry too quickly, bad things happen such as case hardening and honeycomb..

From a literature standpoint, I would recommend that you download a copy of "Drying Hardwood Lumber" and also some of the older USDA FPL manuals on operating a kiln. 

To cut to the chase, for drying 3" - 4" thick slabs in a DH kiln you will first need to air dry for at least a year (maybe less, maybe more), depending upon the species of the lumber.

[Den Socling]

Everybody and their uncle wants to get into the slab business. As Scott describes, it is practically impossible. It can't be done overnight.

[copperhead10]

what makes it impossible? what i have air drying now is hickory 3' wide 3" thick. Been sawed 4 months,have not checked the MC

[copperhead10]

Thank you SCSMITH42 for the advice , do you know of a kiln class in NC?

[Ianab]

what makes it impossible? what i have air drying now is hickory 3' wide 3" thick. Been sawed 4 months,have not checked the MC

Drying thick wood quickly is what's tricky / practically impossible. It simply takes time for that moisture to migrate from the core to the surface where it can evaporate. If you try and speed up the drying you just remove moisture from the surface, which dries and shrinks, while the core of the piece is still wet. Bad things happen, surface checking, case hardening etc.  How bad depends on the species. Heck some species of wood are tricky to dry at 1" thick.

So you are left with very slow drying rates, to give the moisture that time to migrate though the wood. From an economic perspective it's hard to justify tying up a kiln for 12 months to get a load dry, when it could have dried 12 loads of 1" wood in that time.

Careful air drying is an option, but that's going to take a couple of years, then a short time in the kiln to finish the process. Now the slabs can be sold as kiln dried, but you are 2 years down the track before you can sell them.  This is hard to cover in a business situation where you have to sit on 2 years of stock before you see a return.

So that's why those big (and dry) slabs are worth the $$. It took time to get them dry, and time costs.

BTW, Den's speciality is Vacuum Kilns, which are a practical way to dry those more difficult pieces, but not a cheap option, and gets into a bit of rocket science.  ;)

Ian

[thecfarm]

copperhead10,welcome to the forum.

[venice]

It´s not impossible but for the small guy with an conventional DH Kiln looking for quick turn around. I guess that´s what Den is trying to say.

DH Kilns are not really suitable to dry thicker stock. Scotts excellent post out lines what´s involved. To make a business based on thick slabs you would need a High Frequency Kiln or Vacuum Kiln.

venice

edit: ianab has been quicker and in more detail. 1+

[Den Socling]

To correct one thing Ian said, running a vacuum kiln is as easy as rolling off a log. You push a button and come back a couple days later. No samples to check. No adjustments to make. But building them is expensive.

[scsmith42]

Thank you SCSMITH42 for the advice , do you know of a kiln class in NC?

NC State used to have a course on drying lumber that was taught by Joe Denig, but I don't know if they still offer something or not. Virginia Tech puts on a solar kiln operators course a couple of times a year. It is primarily aimed at solar kilns, but the info re how wood dries is the same irrespective of the kiln type.

Ian provides a good explanation of why you can't rush the process. Vacuum is the only way to dry thick lumber quickly, but the capital start-up costs are very high.

[copperhead10]

I am signed up for the Solar drying of lumber at the paul bunyan show in Ohio on oct. 3th and 4th. My goal is not to  dry thick slabs fast, but to dry them right. As scsmith42 said, this is the best place on the web for information regarding milling and drying lumber.

[GeneWengert-WoodDoc]

The Great Lakes Lumber Drying Association (started this week in Antigo, WI, both beginners and advanced) the New England KDA (in NY usually January), Keystone KDA (near State College, but not every year) and Ohio Valley Lumber Drying (often in KY; not every year) all offer drying short courses on a regular basis.

Membership in a dry kiln association is worth it for the tours, technical meetings and training classes they hold.

I do not know of anyone using a DH kiln that can dry 3" and 4" oak without a lot of defects and even with 6 months of air drying beforehand.  You will have a long kiln drying time of six months or longer.  A lot of time and effort to put into a product that will likely turn out poorly.

[copperhead10]

Ok let me start over. my goal is to dry 3" thick slabs with live edges. My slabber will cut 6' wide, so if i find a trunk or crotch this large i would love to saw and dry it as one piece.The goal is to use these slabs inside so the need to dry to 7-9%. thanks for all the comments. I know what i am trying to do is not the norm but the challenge of making unique furniture is what drives me

[tule peak timber]

We cut and dry 3 inch thick, 6 foot wide slabs with live edges like you want to do and it takes time. On oak I figure 2 or more years air drying (my EMC here is about 6 % ) then several months in my DH kiln. Other woods can go faster but even with the time I still get a lot of defects. Really hard to get uniform drying and minimum defects ! Let us know what you end up doing.  Rob

[glassman_48]

tule peak timber,
I am planning on purchasing a bandsaw mill, I have some red oak logs that are 3 to 5 years old and stacked off the ground.  Some friends want me to try to mill some 3 to 4 inch thick by 12" wide fireplace mantels, I was going to leave 1 edge live.  Do you see problems with this?  Thanks in advance. 

[tule peak timber]

Glassman, Sounds good ! If the logs are that old you will have lots of checking, and that looks nice in a mantle. You will also have plenty of bugs and will need to kiln dry to finish off your drying and kill the critters .Hope you post some pics of your project as it comes along. Cheers Rob

[copperhead10]

I have cut 3" thick slabs from white oak, red oak, maple, and cherry logs in the last 4 months.I have stored them a pole barn shed surrounded with stackwrapper black netting.  Would it hurt to move air thought the stacks with a fan?

[tule peak timber]

drying:part art part science...Your particular situation is different from mine (my EMC is 6%) and your pole barn with restricted air flow would work great here. You may develop sticker stain if the drying is not fast enough and you will develop excessive defects if the drying is too fast. On sticker stain I've gone so far as to "roll" the stacks with new stickers, slightly offset, every two or three weeks for a period of time until the MC drops sufficiently to not promote fungal activity. Fresh ,dry stickers helps. Of course "rolling" the stacks adds to the cost of the product, but tiger striped slabs are no good to anyone. I use stickers only 3/16 of an inch thick , along with restricted air flow on oak and that works well here. Certain stickers are prone to color bleed into your slabs so be careful of that mistake (learned the hard way). Also, slow drying gives bugs time to do their work causing more degrade to your slabs. So that said...drying comes from experience balancing several factors...and learning from your mistakes. Cheers Rob

[WDH]

Thick oak slabs cannot stand a lot of air flow like from fans.  A fan blowing thru the stack is too much air flow for green thick oak slabs.  Maple, walnut, and cherry are much easier to dry and are not as persnickety. 

[copperhead10]

thanks for all the info on slabs, I just checked the MC on the 3' wide hickory and it is 55%.This looks like a fall 2015 kiln date

[5quarter]

I don't sell slabs for a living but I Always have some for sale. The trick is to saw em and forget em. As others mentioned, There is a really long lead time between sawing and selling slabs. I just saw my stock, date it and stack it in the machine shed. Takes about 3 years to get 10/4 white oak down to EMC (around 14% mc). Personally, I would not kiln dry any thick slabs until they reached EMC. Not that it can't be done, just my preference.

[addysdaddy]

Gonna jump in here with both feet and ask.... Everyone seems to say that a vacumn kiln is expensive... Since I'm a newbie I guess I can ask ... What does expensive mean... are we talking thousands, more etc... I have a friend who wants to do slab maple up north here in Nova Scotia and a 2 year turn around on product is not an option?  ???

[mesquite buckeye]

Many thousands and there are lots of problems to overcome. Vacuum kilns are not for wimps. :(

[addysdaddy]

Many thousands and there are lots of problems to overcome. Vacuum kilns are not for wimps. :(

Typed 3 responses to that post and deleted them all..