Kerfing and Free Form Laminating
On a Thursday, we normally have ‘Hand Tool Thursday’s’ where our tutor Jim likes to showcase various items from his collection of accumulated and inherited hand tools. However, this Thursday was all about demonstrating different wood bending techniques to the students.
First up was Kerfing. Kerf can be defined as the width of the wood that is removed by the cutting process.
Kerfing is the process of cutting a series of kerfs (cuts) along the side of a piece of wood in close proximity, in order to allow the wood to be pliable enough to follow a curve. When cutting kerfs, the wood needs to be cut deep enough to the edge of the wood that the remaining fibres are free to bend. To cut too deeply will result in the wood breaking in two, or making cuts that are not deep enough will result in the wood snapping. It’s best to experiment, but you’ll most likely find that an uncut width of 1/8 in. or thereabouts works for most woods.
Your kerf spacing will affect both the maximum radius that you can bend, and how smooth your curve will look – the closer the kerfs are together, the tighter the radius you can bend. You can only kerf by crosscutting as to do so with the grain increases the likelihood of the piece splitting.
For the demonstration, Jim cut kerfs that loosely demonstrated the effect. In practice, you would normally use a formula to calculate the exact distance between your kerfs, to achieve the smoothness of the curve you require. Many kerf bending formulas are available online.
While kerfing is an easy and useful technique for bending wood, it is suited to applications where a curve is aesthetic rather than structural, as kerfing does not create a form with great strength.
The magic of kerfing never wanes and all the students (and office staff) were keen to have a play.
Next up…. was free form laminating.
Jim demonstrated a range of different free-form laminating methods using constructional veneer. Take a look at our Instagram feed to see the laminationsglued and clamped into shape, and vacuum pressed.
Constructional veneer comes in a variety of timbers and it is thin and pliable enough to bend. You can simply spread glue on their surfaces and clamp them in layers to the shape that you desire and leave in place for the glue to set. In Jim’s demonstration, the lamination was clamped and wrapped with a ribbon of old tyre inner tube to keep the layers tight together until the glue had set. It is the hardened glue between each layer of veneer that holds the shape of the twist or curve. The multiple glue lines between each layer make the assembly strong, stable and rigid.
As a variation on this method, Jim demonstrated the same concept, but using a vacuum press to hold the shape of the glued layers. The constructional veneer was glued, shaped and then pre-wrapped tight with release film to prevent the breather fabric getting sucked between the laminations, or sticking to the laminate while it is being compressed. As the air is being evacuated, the bag is smoothed out over the assembly to make sure there are no significant wrinkles where it touches the veneer.
The advantage of laminating in a vacuum press is that the process creates an even atmospheric pressure over the glue up, making for a consistent strong assembly.