Bandsaw Washboarding

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Bandsaw Washboarding Bruce Lehmann Thin Kerf Technologies Inc. Introduction
The term washboarding is used to describe a very regular sinusoidal-like pattern that sometimes
occurs on lumber cut by bandsaws and circular saws. Washboarding is a common problem in the
lumber industry and is undesirable because the sawn lumber must be made thicker than normal to
allow the planer to produce smooth surfaces. The necessity to saw oversized lumber results in less
lumber being recovered from the logs, so that significant income can be lost. Washboarding on
unplaned lumber is generally unacceptable. More significantly, washboarding is frequently
encountered when reducing the blade thickness, so it is an important factor that limits the use and
development of thin kerf saws. Although saw filers have trial-and-error procedures that sometimes eliminate the problem, the cause
of washboarding is not fully understood. Changing the tooth shape usually stops washboarding, but
sometimes even radical changes have no effect. The problem is further complicated in that changing
the species of wood being cut affects the appearance of washboarding, indicating that the properties
of the wood are also involved. Description of Bandsaw Washboarding
With bandsaws the pattern slopes downwards in the direction of the blade motion as the wood
advances in the saw. See 1. The pattern begins within 1 inch of the beginning of the cut and covers
the entire depth of the cut. The washboarding usually covers most of the cut surface and can be
described by the horizontal pitch P x and the vertical pitch P y . Other variables used in this paper are: V, the feed speed; c, the blade speed and; P, the tooth pitch. Typical values for a North American
bandsaw are: P = 1.75 inches c = 9425 fpm V = 200 fpm P x = 3.5 inches P y = 1.5 inches A significant experimental result is that the vertical pitch is close to, but never greater than the tooth
pitch. This observation is not a coincidence. Figure 1 Top: geometry of bandsaw washboard pattern. 1 p y ' 1

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