One of the changes in woodturning over the past few decades has been the increase in artistic turning, particularly in faceplate turning such as bowls and vases. This has occasioned the use of woods such as burls, spalted wood and cracked or otherwise injured wood. Many of these require extra caution on the lathe.
Many burls contain bark inclusions, extra knots and wild grain. There may be hidden splits and areas of half rotten wood. All of this means that the burl may give beautiful patterns that are found in no other kinds of woods, but also may deteriorate on the lathe. By its very nature, a burl tends to be unbalanced because the of the varying nature of the wood within it. Thus it will set up vibrations as it rotates on the lathe much as does an unbalanced tire on a car.
Prior to mounting on the lathe, burls should be checked for loose wood and bark. Any loose material should be pried off or glued down with cyanoacrylate glue. Burls should be started on a lathe at the lowest speed and turned until some semblance of balance is reached. Before turning on the lathe for the first time and at each subsequently higher speed, the woodturner should be standing out of the line of fire. Although the loose wood should have been secured, surprises happen especially under the vibration of unbalanced wood.
Spalted woods and cracked pieces as well as those of beautiful but wild grain such as crotch wood, may require special care when mounting. Be sure that screws are strong and well seated. Self tapping sheet metal screws have extra deep threads for a good hold. If using a four jaw chuck, not only should the chuck be well faced to a flat surface but special care is needed to ensure that the recess into which the jaws fit or the tenon that they grab is made of solid wood.
The greatest safety feature that the woodturner can bring to such lovely wood is experience. It is a good idea to practise on solid woods of good quality before attempting some of the more difficult ones. Beautiful woods are found in virtually every country of the world and make for great practise and for great keepers. Burls are the dessert we wait for. Turning piece after piece teaches the mounting skills, appreciation of turning speeds, and tool skills needed for these special woods.
As with all aspects of woodturning, turning special woods with safety is a matter of common sense, experimentation, and experience. Going through a lot of wood in practise is a measure of the enjoyment of the craft.