Timber Frame Lesson 3 | More about Wood

Overview

An aspiring timber framer must learn about the strength and characteristics of wood if they hope to master the craft. The characteristics of wood play a role in the decision process at each step, from general strength characteristics in the designing and engineering of the frame to final weight calculations during the raising and installation of the frame. We will leave a discussion of the design values, to the tomes of books and plethora of characteristic and engineering tables dedicated to this topic. Rather the information here is concerned with the characteristics of wood that go into the decision process of the timber framer where it concerns the timber placement and more specifically layout and cutting of joinery.

The Initial Shake Out

Timbers on Cribbing

Timbers on Cribbing

In our shop, the lead timber framer will place a group of timbers to be worked on cribbing and then shake out the timbers by designating their placement in the frame. The focus at this phase is matching each timber to eventual requirements for strength, function and appearance. This phase takes on an element of artistry that comes from a working knowledge of the whole life-cycle of the tree and hence the timber that sits on the cribs. Some of the this life-cycle is known; what mill or maybe even what woodlot the timber came from, the wood species, and the eventual placement in the building. Other aspects are deduced from looking at the timber; what type of environment the tree grew in, the growth rate of the tree, how the timber was sawn, and the spacing of minor or major branches. Future behavior of the timber can also be predicted; the amount of and effect of shrinkage, the severity and location of checking, even changes such as increase/decrease in wind, sweep, bow, crown and twist. This may seem like a lot of information to process at once and in many ways it is but the decisions are actually made in an instant. All of this information is taken in and processed consciously and subconsciously based on experience. For example, a novice when initially identifing a wood species may be perplexed and may require some sort of reference book. On the other hand, the experienced timber framer will know the species in a fraction of second; either from a glance, the scent, the slightest of touch, or all of these sensory inputs in combination. Similarly within seconds the lead timber framer will identify dominate characteristics of each timber and match it to its eventual location in a building using a grid identification system. But we get little ahead of ourselves here as we are still in the introductory lessons and the above is more on the intermediate and advanced levels of training.

Lessons on intermediate and advance timber framing will be published as well so if you have not joined our other subscribers we suggest you subscribe to our e-newsletter to stay up to date.

Cutting the Joinery

Mortise: Our Mascot

We handcraft all of our frames. Most people when hearing this instantly believe that this is both time consuming and hard work. While this can be true in some circumstances, the reality is that cutting joinery is an absolute pleasure and with skill and experience the work not only becomes easier but faster. Typically, the joinery is roughed out using power tools but then each joint is fine-tuned by hand and tested for accuracy and fit. Mort, our mascot and novice timber framer for those new to the series, got his first exposure to the characteristics of wood by chewing sticks into stringy fronds while he was teething. While seemingly the desire was simply to destroy the stick and relieve his aching gums, it reveals the essential characteristic of wood; i.e. it is essentially a bundle of straws. The comparison to a bundle of straws is useful in visualizing how timbers are composed. Referred to as the “grain of the wood” the wood fibers can be long and stringy or short and dense depending on the species. The grain grows around aberations such as knots, branches and/or deformities often in bewildering and amazing ways. The wildest changes in wood grain direction are often referred to as highly figured wood and is prized for its natural beauty. The essential point to realize is that though the timber may be straight the wood grain may not be. Indeed the grain differs greatly depending on which side of the heart(the center of the tree) you are working.

As the timber framer’s chisel slices along the grain, lets say while paring a joint you will feel this change in wood grain. Watch a timber frame crew at work and you will notice the novice flat-footed muscling their way through the changes in wood while the veteran dances around the joint shifting their position and posture to best let the tool do the work. By fighting the wood grain, cutting the joint becomes …. well work. On the other hand, by reading the wood grain and working with the natural characteristics of the wood the wood comes off with ease. The trick is not to fight the wood, to allow the chisel to move in a sweeping not straight motion and to let the wood guide your hand and chisel to the path of least resistance. Success comes with long, often paper thin, shavings. But knowledge of wood grain not applies to the graceful paring of tenons and similar joints, but also to chopping of mortises and housings. Quick powerful but precise strikes of a chisel and mallet will also yield dramatic results. The work become less about strength but more about knowledge of where and how to strike to yield maximum results with minimal effort. Put this altogether and you will see why we love the art and craft of timber framing.

Would you like to see a live demonstration of these principles and techniques? We will be holding a live demonstration on June 25th. Check out the details here!

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