When to mill a log into lumber?

[James Baker SD]

A neighbor gave me some sections of a tree he cut down. I painted the cut ends with Green Wood End Sealer from Rockler. Being too busy at work and not having the best health, the wood sat for about 2 years. I looked at it last weekend and every piece is so badly checked and/or split that I would be lucky to get a picture frame or two from it now (these were from 4" diameter to about 8" diameter and from 3' long to abut 6' long).

Question, it seems I messed up by waiting too long, so when is the ideal time to mill lumber from such a log? I thought if I let it dry some it would warp less when I did cut it up. Of course, my "dry some" got extended more than I originally planned.

James

[Al Weber]

It is generally best to mill a log as soon as possible after cutting it. Sealing the end grain is the right thing to do but just as important is where the log lies. Is it above ground and dry? What kind of tree was it? I've milled cherry that was well over a year old but sealed and stored outside but off the ground. I've also seen maple that is worthless after a few weeks if it is on the ground.

[Neal Clayton]

it's even beneficial for some species to let the logs sit in the rain for awhile ;).

for sap rich species, like the various yellow pines, the rain will wash most of the sap from the log, whereas if you mill it green the sap will remain indefinitely.

[Frank Drew]

I agree with Al that the sooner the better when it comes to sawing up a log but he's also correct that if the log is up off the ground and not in direct sunlight you might get lucky.

A sawyer I used to deal with sold me all the wood from a walnut log he'd had so long that the bark had fallen off; even though he didn't saw it through-and-through as I'd requested (:mad:), the material was still very, very nice, with no degrade from having sat in the round so long. But I consider that example the exception.

In the old days, saw mills had ponds (mill ponds) where they could keep logs until they were ready to saw them; the water kept them from checking.

[Danny Hamsley]

Cutting the log green is best then sticker stack the boards to dry under a roof but open to the air for good circulation.

[Pete Bradley]

At 4-8" in diameter you didn't start with much and what's left is probably best used as firewood. However, I suggest you split or slice one of the bigger ones and see what's in there. I once rescued a birch round that was intended for the fireplace because it had spalted into an amazing pattern of pinks, browns, and blacks. If it's a tough species like ash or hickory, you can probably salvage some nice mallet heads or tool handles.

Pete

[Scott T Smith]

For furniture grade lumber, it is very well documented that logs start to degrade immediately after they are felled. The USDA manuals cover this, as do the manuals written by lumber milling and drying experts Dr. Eugene Wengert of UWVA and Dr. Joe Denig of UNC.

In order to minimize degrade, the best process is to fell the tree, buck it to length and end seal on day 1, mill it into boards on day 2, and get the boards into a kiln on day 3.

Any increases between these steps will lead to increased degrade - period.

Soaking the logs in a water pond or keeping them wet by spraying them with water is better than leaving them sit in the air, but degrade still occurs.

Lumber does not dry properly "in the log", only "in the board". Leave your logs standing as trees until you need them, and then get them milled and stickered quickly.

One caveat; if you want spalted lumber you need to let the logs sit for a while - usually through at least one hot summer.

[Frank Drew]

In order to minimize degrade, the best process is to fell the tree, buck it to length and end seal on day 1, mill it into boards on day 2, and get the boards into a kiln on day 3.



Scott,

I'm with you that converting logs quickly is generally the best plan, but, unless you were overstating your position for effect, I don't agree that your day 3 plan (into the kiln) is necessarily the best way (or the only good way) to ensure quality lumber, and I certainly don't agree that you can be dogmatic that any deviation at all from your ideal schedule will inevitably result in lesser quality material.

[Mr. Jeff Smith]

Noob here, is kilning the wood a requirement?

I recently had to pull down a tree, was going to try and mill the wood (first time), but don't have a kiln, may have to look for help around town. Thanks.

[Nathan Palenski]

I know a couple of people who built solar kilns. They're not left with as high quality a product as electric kilns but its better than stacking wood in your livingroom so the MC drops to the house equilibrium.

[Cody Colston]

I always thought, heard, read that air drying for a period of time before kiln drying was better than going directly into the kiln. Some (James Krenov) would even argue that totally air dried wood made better furniture than kiln dried wood. That is somewhat substantiated by period furniture that is over 200 years old and still looking great. All of it was air dried.

FWIW, I regularly see huge stacks of Red Oak logs at the sawmills around here that have a sprinkler system to keep them wet until they are milled.

[Steve Peterson]

A round log will generate lots of splits between the center and the bark. Would splitting the log once through the center while it is green allow the log to shrink without much further cracking?

Of course, the ends should still be sealed to prevent them from drying faster than the rest of the log.

Steve

[Frank Drew]

Noob here, is kilning the wood a requirement?


No; most commercially available furniture woods have been kiln dried, of course, but as I implied and as Cody explicitly stated, air drying is also a quality option given the right conditions (right location, proper stacking and stickering, plenty of time...)

[Scott T Smith]

Scott,

I'm with you that converting logs quickly is generally the best plan, but, unless you were overstating your position for effect, I don't agree that your day 3 plan (into the kiln) is necessarily the best way (or the only good way) to ensure quality lumber, and I certainly don't agree that you can be dogmatic that any deviation at all from your ideal schedule will inevitably result in lesser quality material.


Frank, sorry for being so "frank" in my response.... it was after a long day and it could have been worded better. You are correct in stating that "quality lumber" can be obtained by different processes; my point was aimed more at the ideal environment and quite frankly I was thinking along the lines of higher volume production drying versus home drying.

By the way, the way that you worded your "disagreement" was excellent!

Dr. Wengert has been pretty adamant that degrade increases when the steps involved in the entire process are lengthened. A number of years back he conducted a comparison, and found that it the economics were much better by getting into the kiln sooner rather than later, as there was a higher yield of higher quality lumber.

Degrade though, refers to end checking, warps, cups, etc, and we're talking about small percentages (such as 2% more degrade if you wait a couple of weeks to get into the kiln). For the average home dryer, 2% is no big deal, but for for a company drying a few million bd ft per year the economic cost really adds up and I think that Dr. Wengert's comments were directed at this audience. Thus, my comments were really not well thought out with respect to this audience; and thank you for pointing that out and allowing me to clarify.

Cody, I think that Mr. Krenov was comparing AD wood with KD wood from "conventional" kilns, which use high temperature (160F or higher) to dry.

Today, many small to mid-size kiln operators use dehumidification kilns, which dry at low temperatures, and more closely mirror the workability of air dried wood.

Each species and thickness has it's own ideosyncracies when drying. Many wood species are very forgiving during the drying process; in general these are the species that can tolerate relatively fast moisture removal (pine, cedar, etc. Some species are in-between, such as walnut and cherry. Some species are much more difficult to dry properly; namely oak and sycamore.

The ease and quality results from air drying vary depending upon climatic conditions. Climates (or seasons) that are cooler are much more forgiving for air drying, versus hot climates. Drying rates are dependant upon three factors - temperature, relative humidity, and air flow. Higher temperatures and higher air flows increase the rate of drying, as does lower RH.

Here in the south, if I intend to air dry a slow drying wood such as 8/4 oak, the ideal time to log/mill it would be in the late fall, when the temperatures are below 70 degrees. By the time that the next summer rolls around, the internal moisture content on the planks should be below 35%, which is a safe range for increased drying rates.

If I were to mill these same planks in July and then air dry them in the 90+ degree temps, chances are that I would have 40% or greater degrade.

Thus, with slow drying species such as oak, kiln drying during the entire process is preferred because you can closely control the entire process.

Presuming that your boards are properly stickered, almost all damage that occurs during the drying process happens when the boards transition from green down to 35% moisture content. However, the damage does not become easily discernable until the moisture content is much lower.

To sum up, air drying a slow drying species such as oak during the early stages usually yields acceptable results if you start the process in the fall, or live in a cooler climate. For faster drying species, it's not quite as critical.

In addition to close control of the drying process, kiln drying does have one major advantage over air drying, and that is the sterilization treatment at the end of the drying process. Any residual pests such as powder post beetles, etc, are killed during sterilization and this reduces the potential situation of building a piece of furniture only to have bugs starting to crawl out of it a few months down the road.

It really is much better to dry boards, as opposed to drying logs. For one thing, a 4/4 board usually experiences consistent drying from both sides; a split log is only drying along the split surface and when it is finally milled into boards it will vary in terms of internal moisture content, which will cause movement.

[Joe Chritz]

It appears Scott has some experience in larger scale drying operations. Perhaps you can answer a question concerning the operation.

Isn't there a reaction to the heat that "sets" the cell structure and increases the resistance to regaining moisture as easily? I know about setting pitch in softwood as well as the benefits of killing bugs.

I used about 150 BF of air dried red oak a year or so ago on a kitchen and all the boards were as good as any kiln dried stuff I had found. This was partly from the milling and storage to the fact that the tree was fairly large and a lot of the lumber was boarding on rift sawn.

Joe

[Frank Drew]

Scott,

Thanks for your very informative followup.

What's the time difference, if any, between conventional kiln drying and dehumidification kiln drying?

Also, what's involved in the sterilization treatment at the end of the drying process? [Of the wood I've used, ash has been the most prone to powderpost beetle damage.]

[Cody Colston]

Scott,

You obviously have a much broader knowledge of kiln drying lumber than I have since I don't have any at all. :D

I can also see how the degrade factor would become more significant if working on a very large scale as compared to a one man operation. Thanks for the info.

[Richard M. Wolfe]

Since you started with such small logs and they have been sitting for such a long period I would doubt that much can be gotten from them. We don't try to do anything with a log less than about 12" unless it's a special case for some reason. Take a look at the end of a log and visualize boards out of it....not much to be had from a eight inch log and what is there is a lot of wood from the very center, which is noted for splits and checks.

Depending on species, conditions and the operation itself some will air dry for an initial period to get rid of a lot of the water to minimize kiln expense. But the larger drying operations have to maintain as uniform an end product as possible with minimum degrade as well as cycling wood through as fast as possible so will do all the drying in a kiln.

[Scott T Smith]

It appears Scott has some experience in larger scale drying operations. Perhaps you can answer a question concerning the operation.

Isn't there a reaction to the heat that "sets" the cell structure and increases the resistance to regaining moisture as easily? I know about setting pitch in softwood as well as the benefits of killing bugs.

I used about 150 BF of air dried red oak a year or so ago on a kitchen and all the boards were as good as any kiln dried stuff I had found. This was partly from the milling and storage to the fact that the tree was fairly large and a lot of the lumber was boarding on rift sawn.

Joe

Joe, the only reaction that I am aware of is case hardening, which is not a good thing... Other than that, KD wood will definitely regain moisture and equalize with it's environment. I have heard that there is an experimental ultra-high temperature process being trialed in Europe that may prevent moisture regain, but the jury is still out regarding it.

Frank: The kiln schedules - time wise - are fairly similar for conventional and DH drying for most hardwoods. Fast drying species such as southern yellow pine can be dried much more quickly in a conventional kiln.

Re sterilization, it varies depending upon the temp. You can sterilize as low as 120F, but it takes several days at that temp (measured at the core of your boards). The general requirement is for the center of the wood to reach a temperature of 133F or higher for at least 30 minutes. There are several factors that influence the time though, including species, thickness, and MC%.

Personally, on 5/4 lumber I run a 24 hour sterilization cycle at 135F after the boards are below 10% MC. This provides ample time for the core to reach 135 (I usually start at 120F), and an extra safety margin.

[James Baker SD]

Since you started with such small logs and they have been sitting for such a long period I would doubt that much can be gotten from them. We don't try to do anything with a log less than about 12" unless it's a special case for some reason. Take a look at the end of a log and visualize boards out of it....not much to be had from a eight inch log and what is there is a lot of wood from the very center, which is noted for splits and checks.

Depending on species, conditions and the operation itself some will air dry for an initial period to get rid of a lot of the water to minimize kiln expense. But the larger drying operations have to maintain as uniform an end product as possible with minimum degrade as well as cycling wood through as fast as possible so will do all the drying in a kiln.

As I wrote initialally, a few picture frames will be the most I can hope for, if even that. The neighbor asked if I wanted the wood, and I thought it would be interesting to try to mill it. I do not have any mill, only a bandsaw with 11" resaw capacity for cutting. Most of the delay was trying to figure out how to guide even these small logs thru the bandsaw--what jig I might make, etc. If I had milled it in time, I have no kiln so the wood would be air dried as well. I live east of San Diego in the desert with average humidity about 10% to 15% year around and daytime winter temps in the 70's, summer 95-100's. I am a weekend hobbiest (when I am lucky with time) and just was curious what figure I might get from an unknown log.

James