Ring Count

[Bob Smalser]

“Hi Bob, Could you possibly create a post explaining why and how tight ring counts
improve lumber qualities? I know that tight ring counts are preferred, but why is it better?”

My pleasure…it’s really quite simple, looking at a close-up of the growth rings:

http://pic3.picturetrail.com/VOL12/1104763/3075040/53114962.jpg

In early spring the wood grows quickly with large, thin-walled cells…”earlywood”…seen as the lighter colored portion of the growth ring. As the season progresses and growth factors such as light, temperature, nutrients and water become more limiting, the cells get smaller, thicker-walled, denser and more resinous…”latewood”…seem as the darker portion of the growth ring. You can actually see the cells get smaller in the photo as they darken. Smaller, denser cells with more natural resins are stronger…and a higher proportion of them in the wood makes for stronger and more durable timber…significantly stronger and more durable timber.

Even in the tropics there is usually some limiting factor to create latewood…like an annual dry season…and it is the rare tree that doesn’t show some sort of growth ring.

http://pic3.picturetrail.com/VOL12/1104763/3075040/53116512.jpg

But it also helps to understand something of how the tree grows…many folks think of growth rings in three-dimensional form as cylinders, but they are really cones as shown above. That’s useful to understand when ripping bending stock from wood originally milled from a cant as most sawmills do…there is almost always some grain runout in straight, sawn boards that should be identified before selecting stock for bending. That’s why riven or split boards like the Vikings’ early lapstrake planking are almost always stronger than straight boards, and for most store-bought wood, boards milled from nearer the pith will have less grain runout.

http://pic3.picturetrail.com/VOL12/1104763/3223936/39972549.jpg

There are some sawmills that can compensate for log taper without making a cant, taking their waste from the pith rather than the slab…the Lucas and Peterson swing-blade mills come immediately to mind. If you can find a local sawyer using one and explain your requirements, you can obtain higher quality bending stock.

http://pic3.picturetrail.com/VOL12/1104763/3075040/53116506.jpg

Wood is composed of hollow, spindle-shaped cells of cellulose cemented together by lignin and arranged parallel to each other along the trunk of the tree. Trees grow by adding cells in the (again, cone-shaped) cambium layer immediately beneath the bark…the trees’ existing cells do not grow larger. Thus new wood is laid down atop of old and the diameter of the trunk increases…stretching, cracking and sloughing off the bark as the tree grows.

The wood immediately beneath the cambium layer …the sapwood…stores and transports the tree’s water and nutrients. As sapwood contains much water and minimal resins, it is never rot resistant…even in rot resistant species…and is undesirable for use in boats. Generally, the faster the tree species grows, the higher percentage of sapwood…yellow pines from modern plantations take decades to develop heartwood and today’s SYP lumber generally contains no heartwood. Black Locust is an exception…a fast-growing pioneer species that generally only contains a half-inch of sapwood and high rot resistance and strength in its heartwood…hence an excellent boatbuilding timber to propagate.

Heartwood consists of dead, inactive cells that no longer transport or store food and water. The transformation of sapwood to heartwood is accompanied by a general loss of water and a dramatic increase in the “extractive” content…the resins, tannins, gums, oils and minerals that give heartwood its distinctive darker color and in some species resist rot.

Most woods like also have “rays”…which are horizontal cells that transport water radially across the grain. In White Oak these cells are larger and more conspicuous, especially in quartersawn wood. “Tyloses” also occur in some hardwoods like W. Oak, ash and hickory. These are ingrowths that clog the sapwood’s pores as it transforms to heartwood and prevent water transmission. This makes White Oak excellent for boats and cooperage, but also prevents the penetration of preservatives in the wood, so there is a trade off. Softwoods transmit water differently than hardwoods…they transmit water from longitudinal cell (tracheid) to longitudinal cell and don’t have pores…. that’s how you tell a “softwood” from a “hardwood” botanically, not from the leaves. The Ginkgo or Maidenhair Tree in your local park is certainly a broad-leafed tree…but it also has tracheids and is really a “softwood” botanically.

http://pic3.picturetrail.com/VOL12/1104763/3075040/52135894.jpg

As a practical example above, here’s a Doug Fir log in my stack yard recently harvested from a neighbor’s farmstead. The tree above is what we call locally a “mini-old growth”. It was a seedling in 1900…well before the area was first selectively logged in 1936…yet it is only 21” in diameter. You can see that as a seedling, it had a tough time competing with its larger forest neighbors, and there are 20 rings to the inch until its larger neighbors were thinned in 1936. Then with more, but not full sun, the tree grew at a rate of 8 rings to the inch…and you can see those rings tighten up some as its neighbors also shot up…until the area was completely cleared for a farmstead in the 1970’s, where it got full sun and grew at an even faster rate of 4 rings to the inch.

http://pic3.picturetrail.com/VOL12/1104763/3075040/52135880.jpg

In contrast, its close neighbor was also the same size…around 21”…yet this tree didn’t sprout until the around 1975 when the farmstead was cleared, and has spent its entire life in full sun…3 rings to the inch.

There’s little doubt which log will become boat framing and which log will become studs.

[Ken Fitzgerald]

Excellent information and explanation! Thanks for posting!

[Dave Anderson NH]

I always enjoy your informative article type posts. You seem to have a knack for relating the technical aspects of wood to practical examples and illustrate them well. Thank you.

[Brent Beelby]

Love your posts Bob. I live just north of you up in Vancouver and I just finished remodeling our bathroom. A freind of mine brought me some rough 2X6 about 10 feet long quartersawn red cedar from the queen charlottes. I did the counters out of it. I knew it had some tight rings so I just went and counted some of it. In some spots it has 26 growth rings per inch. By the way Bob I've seen alot of red cedar here where I live and I dont know if it's because the wood was old growth or if it's because it was quartersawn but it didn't look anything like red cedar.

thanks, Brent

[Bob Smalser]

Some excellent comments from other forums, FYI:


Originally posted by R:

But, but, but... IIRC in ring-porous hardwoods like oak,ash and hickory,low ring counts and fast growth make stronger material because,the porous part of the wood(latewood) is weaker.Fewer rings per inch mean more solid wood per inch.



Originally posted by M:


One thing you didn't mention was the difference between ring-porous and diffuse-porous wood. The way you described earlywood and latewood applies only to ring-porous, or open-grain, species like oak, ash, chestnut, elm, and hickory. But in diffuse-porous, or closed-grain, species like beech, sycamore, maple, cherry, birch, and sweetgum, the pores are distributed "randomly" thoughout each annual ring. That's why many woodworkers disparage open-grain woods, especially if they're fast-grown, as "coarse." You've got that density gradient going back and forth (which is exacerbated in fast-grown wood), causing tearout and other manifest inconveniences.

With the oaks--which I'm most familiar with--fast-grown wood is stronger than slow-grown, because most of the wood in wide rings is the denser latewood. But slow-grown oak is a much nicer wood to work with because its texture is more even overall.

Another point regarding ring-width and strength is that most "softwoods" are topsy-turvy from ring-porous hardwoods, in that most of the wood in each ring is the less-dense earlywood. This causes slow-grown softwoods to be harder and stronger than fast-grown.

I think most folks on this board who have an opinion would agree that the definitive text for all this sort of info is R. Bruce Hoadley's _Understanding Wood_, Taunton Press, 2000.


Written in the context of boatbuilding softwoods…your comments are excellent…I probably shoulda left more-complicated hardwoods out entirely. I agree with you, and have certainly read that before...but not having much oak out here to play with, I wonder what the strength differences really are?

I doubt shipwrights (and ships) of the 16th and 17th Centuries when those original virgin oak forests were used thought it to be much of a disadvantage…after all, those uneven-age forests had younger, sun-grown trees to select from, too.

Doug Fir has been downgraded in strength a couple times since the 1930's as an engineering material...minor downgrades...the last downgrade quite recent. My lumber grader the other day thought the reason for the downgrade was because,"…it wasn't as strong as we thought it was." My answer was yes, but there's little doubt in my mind as to why when you look at the two example logs from my stacks.

Perhaps the difference between new and old oak is akin to the DF dynamic only in reverse?

[Tyler Howell]

School is good. Thanks Bob.

[Chris Padilla]

Ah, the science of wood and trees! Very cool...thanks for the physics lesson! :)

[Bob Smalser]

More from a sawyer in Australia:


Bob I have never heard of fast grown wood being stronger before. Is this only for Oak, Ash & Hickory or for all hardwoods? I can grade wood here (Australia) Pine can fail visual grading if any of the growth rings in the inside 100mm diameter are over 13mm whereas ring width does not get a mention in hardwood grading.
I read somewhere that the sap wood in hickory is the best part and that the heartwood was not as strong do you know anything about this? That's what the discussion above is about. The argument is that in "ring-porous" like oak, ash and hickory as opposed to "diffuse-porous" woods like cherry and maple...woods that have pronounced, open pores in rings....that those ring-porous woods are stronger with fewer rings per inch.

The logic is there, well enough...the question is, how much stronger or weaker and is it significant?

We don't have many of these woods out west in any quantity and I don't mill them much....no oak expert here, by a long shot...but the family milled oak when I was a kid back east and having used a bit of it...including 200+ year-old W. Oak...I suspect the issue is overstated:

1) What you lose in more pores you gain in a higher proportion of smaller, latewood cells just like in softwoods.

2) The gains in terms of durability from higher extractive content in the latewood are well worth any minor strength issues.

3) I haven't seen any results of lab testing on this to determine any differences on strength and would want to before drawing firm conclusions. Doug Fir, in contrast, is tested frequently because it's our Number One structural wood over here.

I just ordered am 8-dollar copy of Hoadley's out-of-print book, "Understanding Wood", because that's where I've been told the issue is raised....I'll let you know...."Because I said it is" or modern lore passed down through magazine writers doesn't cut it - I want to see the numbers. I also asked the question with the forestry/sawyer extension professors to see if they have any test data available.

Wood for bending is a different issue and wood from young second-growth trees is preferred because of pliability. Faster growth and correspondingly larger cells are desirable here.

[Tim Sproul]

I think the strength issue is moot....unless you are talking construction lumber.

wood strength for furniture is for the most part, much stronger than needed...and you can most times just use a bit thicker board if needed.

building homes and such is an entirely different issue....

[Bob Smalser]

I am talking about structural lumber, Tim...for boats...and will run this down like I've done some others.

One problem since the great craft revival of the 70's is that folks write books with statements in them that apply to one facet of woodworking but not another, without a good understanding of what the other guy's requirements are. I haven't read Hoadley yet, so I'll not jump to conclusions...but some of this is present in even the best works.

Hack's handplane book is an excellent example....bought it at y'all's recommendation, in fact...great book but not once does he mention boatbuilding planes or boatbuilders and all his conclusions about woodies are based on cabinetmaking and coachwork. That's not necessarily wrong...but it's certainly incomplete as boatbuilders have been and remain to some extent the major haven of wooden planes. Not only lighter, but after using a Stanley 113 all day doing outboard joinery, you'll soon make your own fixed compass plane or planes to replace it, just like you'll prefer a transitional to a cast iron plane for working overhead.

These written statements quickly become lore and are the source of a number of problems....selling airdried Western Red Cedar to eastern boatbuilders is one example. Almost everybody back there will tell you WRC is brittle because John Gardner's and Greg Rossel's books says it is. Much as I love and respect those guys, the USDA numbers don't bear that out, and running the issue to ground I find that all these authors likely ever tried was kilned WRC stock. It so happens that WRC logs vary dramatically in M/C from log to log....from as little as 30pct to as much as even 90pct...and putting a railway car worth of WRC lumber in a kiln from hundreds of such logs will mean some of it is overcooked and brittle. In the meantime, we builders get to keep all that great oldgrowth cedar to ourselves out here...but we sawyers don't get to ship any of the good stuff back east very often as the market is poisoned.

So I'll just keep asking the questions and try to document the answers...the base knowledge certainly applies to cabinetmakers, too.