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Pressure Bar Adjustment for Veneer Lathes

Pressure Bar Adjustment for Veneer Lathes

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Setting the Bar Pressure

A lathe pressure bar is designed to compress the veneer bolt into the cutting edge of the late knife. This compression, when properly applied, ensures a smooth surface, a tight back, and more uniform thickness than is achieved when veneer is peeled with little or no compression. The compression is a fractional force between the bearing strip on the pressure bar and the log, is exerted both horizontally and vertically

Horizontal pressure is the setting adjusted more frequently as the lathe operator attempts to smooth out the peel during the cutting process. To set the correct horizontal gapBaldwin (1981) suggest the following steps

  1. Set the pressure bar parallel to the cutting edge of the knife. The distance between knife tip and pressure bar is measured with a machinists rule or dial indicator.

  2. Systematic measurement and adjustments should be made by the lathe operator at intervals across the bar. The adjustment screws, located on the back side of the pressure cap, are used to increase or decrease the distance between knife tip and pressure bar.

  3. After the initial setup, the operator visually inspects the veneer. Final pressure bar adjustments are made on localised tight or loose areas. These adjustments require a practised eye and compensate for any slack that may occur because of lathe wear.

  4. A staring point is obtained by setting the horizontal opening to a distance equivalent to 80 to 95 percent of the peel thickness, the distance varying with species being cut.
Shelling and tearing of fibres indicate that too much pressure is being applied resulting in rough veneer and spinouts. Optimum surface smoothness is obtained by using slightly less pressure than that causing veneer damage or core loss.

Vertical Pressure Bar Adjustment

The vertical pressure bar adjustment is obtained similar to horizontal pressure. A machinist's rule is used to measure the distance from the knife tip to the upper roller bar lip. With the nose bar, a feeler gauge generally is used to measure the gap at both ends of the bar. With both types of pressure bars, the lathe cap is closed to bring the pressure bar close to the knife. The pressure bar then is adjusted up or down until the selected setting is reached(Baldwin 1981).

More accurate roller bar settings can be obtained by using a gauge expressly designed for this application. One widely used design requires notching the upper roller bar lip near each end of the bar. The distance from the top of the roller bar to the knife tip is measured, the reading is shown on a dial indicator. Baldwin (1981) suggests this setting method is quick and convenient.

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