Science & Design - DVD
Produced by Passion for Wood, Ontario, Canada
As reviewed in The Australian Woodworker Issue 153
Most woodworking books deal with skills, techniques and projects, but what about the material itself - wood?
In his fourth DVD set Hendrik Varju from Passion for Wood discusses the unique properties of wood and how a good design must allow for these properties or the piece will fail.
Advanced woodworkers will know most of the material covered in this set but novices and students will find the video both highly informative and entertaining. Hendrik describes his videos as one-on-one tutoring and this set is no different. He makes the rather dry topic very enjoyable to watch and listen to.
He makes particularly good use of the video medium when he demonstrates the porosity of wood by blowing bubbles through a series of solid boards. On one sample he shows the effect of non-linear grain direction.
The timbers used throughout the DVDs are Northern Hemisphere species, but the information provided is universal and can be applied to any wood you may use.
In the first chapter he discusses the basic structure of wood, including the tubular nature of this 'solid' material, growth rings, earlywood and latewood, sapwood and heartwood (also known as truewood), knots and branches. Differences in these features affect the properties of a given species or tree.
The next chapter deals with the different cuts, in particular flatsawn (we call backsawn), riftsawn and quartersawn. The type of cut affects not only the appearance but also the wood movement (which is covered at length later).
Another feature of the tree's structure is the medullary rays. Hendrik discusses their impact on the board’s appearance, particularly with quartersawn cuts.
Having covered the physical structure of the tree, on the second DVD Hendrik proceeds to examine the importance of tangential and radial movement (and why longitudinal movement is usually ignored).
Timber movement is affected by relative humidity and moisture content, so he discusses how this affects the treatment, purchase and storage of cabinet grade timber, as well as problems with cracking and distortion.
Joint design and construction introduces a whole new range of problems associated with timber movement. He covers the conflict created by non-aligned grain in adjoining members and the effect of the width of members on the stability of the joint (ie. a wider board experiences more movement).
Throughout the discussion of movement and design, Hendrik clarifies his comments with practical examples, either drawn on his paper 'whiteboard' or with the aid of timber samples on his workbench.
As he points out, some designs invite failure, either by cracking the board or breaking the joint. He suggests redesigns which eliminate or mitigate the problrem.
How much is too much? Movement can be constrained by limiting the width of members. Hendrik provides a few rules of thumb for design work.
He also examines the use of movement calculations and gives a number of examples of their use. Australian timbers will have different values but the principles are the same.
While general movement problems can usually be overcome by making allowance for them, some fine woodworking applications require a more precise determination of the expected change on dimensions. In these instances the use of calculated dimensions for movement is essential, to prevent drawers binding or panels cracking.
The third DVD deals with specific design applications.
The boards in a table top need to be laid out and glued together in such a minner that any distortion is minimised. The top is then secured to the table frame with steel buttons or other devices to hold it securely yet allow movement.
In frame and panel construction the panel is also made by gluing boards together. In this instance the panel must be left free to expand and contract within the confines of the frame.
Hendrik’s third example is what he calls an endcapped breadboard. The end grain of glue-up panel is concealed by a member running perpendicular to the boards. While aesthetically pleasing, it is a recipe for disaster if the endcap is securely glued to the panel. Instead he demonstrates a pinned tenon arrangement that secures the panel in the middle of the endcap yet allows movement across the rest of the panel.
As an example, he shows how the same concept can be applied to a wide (bed) headboard attached at either end to a leg.
In the Furniture Tour segment he critiques a variety of furniture pieces including a trestle-style table, dining table, framed coffee table, chair, shelf unit, bedhead, bedside table and blanket box.
With each item he discusses the wood movement issues involved and how the design managed them. In his usual informal style, he not only lists the design features used but also crawls under the furniture to point them out.
Finally, in his Thoughts on Woodworking footage, he talks about the use of wide boards versus narrow boards, practical humidity control for the weekend hobbyist and the concept of good design.
By the end of the video the viewer will know not only a lot more about wood and what determines its properties, but also how to select suitable boards or blanks for a project irrespective of the species involved and how to design and build to allow for wood movement.
While this DVD set will interest most woodworkers, its greatest appeal will be to novices, students and inexperienced woodworkers who will benefit enormously from Hendrik Varju’s presentations. For this reason Wood Science & Design is very highly recommended for the libraries of woodworking Clubs, schools and TAFE Colleges.
Duration: 5hrs, 54mins, 3 discs
DVD - English - NTSC