Information on setting the knife and bar in a lathe ass […]
Information on setting the knife and bar in a lathe assumes that the knife frame and bar frame of the machine are in proper alinement with the center of rotation of the spindles. Similarly, it is assumed that the knife and bar ways on the slicer are level and perpendicular to the flitch ways. It is further assumed that there is a minimum of play in the moving parts
of the lathe or slicer and that the machine parts are at the same temperature they attain in use. If these conditions are not met, the careful setting of the knife and bar on the static machine may be changed so much in the dynamic cutting condition that poor quality veneer will be produced.
A correctly ground flat knife with a straight cutting edge is the first requirement. If a knife holder is used, it must also be clean and flat. A clean, flat bed on the lathe or slicer is the second requirement. The knife or knife and knife holder is then set on the two end adjusting screws. The clamping screws are tightened by hand and so the knife is flat against the bed but free to move. To this point, the procedure is the same for the lathe and the slicer.
Setting the lathe knife. - After the knife is resting on the two end adjusting screws on the lathe, the knife edge is raised until it is level with the center of the spindles. This can be facilitated by using a template consisting of an accurately machined wood block cut out at one end to one-half the diameter of the spindle. The cutout end rests on the spindle and the other end on the knife edge. The height of the knife is then adjusted until a spirit level on the back of the template indicates level. The same adjustment is then made at the other end of the knife. If the span is short and the knife deep and stiff, the knife height should be the same across the lathe. However, with longer knives, particularly those that have been ground so they are not so deep, the knife may sag in the middle. One way of checking this is to level a special transit with a telescope about 20 feet from the lathe and swing it from one end of the knife to the other. The knife edge should be in line with the crosshairs along its length. If the knife sags in the middle, it should be raised with the leveling screws near the center of the knife. Once the knife edge is true, some operators make scribe marks on the lathe so they can reposition knives with precision. Another method is to measure the extension of the knife from the top of the knife bed.