K for Knots                                  

One way of defining a knot is simply a branch that the tree has either grown over or grown around. The knot therefore shows as an irregularity in the grain structure of the wood.  There are three types of knot which are found in wood:

• The inter-grown or tight knot occurs where a living branch has been incorporated into the tree as it grew. This type of knot does not affect the wood strength.

• The encased or loose knot occurs where a dead branch has been incorporated into the tree. This type of knot is not attached, is more likely to fall out and reduces the strength of the wood.  

• The spike knot occurs when the surface of a piece of wood cuts through a length of branch - these can be tight at the base and loose at the end.

The resulting weaknesses which knots can produce require special care when turning wood with these features.  Various options for dealing with loose knots include knocking out loose knots and using the void as a feature in the turning, using 5 minute epoxy glue to fix loose knots in the wood or using slow set epoxy glue and colouring to fill the void around the knot

When turning wood containing knots it is advisable to:’

1. keep turning tools sharp,
2. keep the lathe speed up,
3. take light cuts and to use smaller sizes of turning tool.

These will help to minimise the forces which the turning tool will exert on the knot and reduce the likelihood of the knot being forced from out of the wood.

LEARNING POINTS

Do not try to turn pieces with loose knots in them until they have been removed

or secured in the wood.

When turning wood containing knots aim to minimise the force which is

exerted on the knots.

For illustrations see  Knots in wood from American Woodworker