Slicing Knife on Lathe and Slicer Many have observed that the first sheets from a flitch on the slicer and the first few revolutions of veneer from a bolt on the lathe are thinner than the nominal knife feed. Hoadley (29) studied this phenomenon with a knife and pressure bar mounted on a pendulum dynamometer.

He attributed the thin first cuts primarily to compression of the wood beyond the thickness of cut, followed by springback after the cut. With the same advance, both the compression and springback became progressively larger until a full thickness chip was produced. Hoadley called this dynamic equilibrium. Later studies on both an experimental and commercial lathe at the Forest Products Laboratory Hi) indicated that the thin cuts were due mainly to takeup of slackness in the lathe.

Veneer cut from a small, more rigid experimental lathe reached full thickness quicker than veneer cut on a 4-foot-long commercial lathe. When the pressure bar was against the wood, it tended to force the bolt and knife in opposite directions. When the bar was retracted and the knife alone engaged the bolt, the knife and bolt were drawn together.

As a result, opening the bar (for example, to clear a splinter) during cutting results in large changes of veneer thickness on a lathe that has slackness. In contrast, if the pressure bar is kept closed from the start of cutting, then much of the slackness in the lathe will be taken out by the time the veneer is wide enough to use.