Date: 2008-05-06
By Jim Effner
It's a simple fact. Reducing kerf will increase yield. However, there are many other factors to take into consideration.
Most rip or cross parting cuts made with a circular saw are not made with the thought of just how much material is going into the dust collector, as opposed to remaining with the stock being cut apart. That is, most of our attention is directed at either the finish quality of the surface after being cut or how fast we were able to accomplish the task.
In examining kerf and stock yield, among the first things we discover is that conventional saw blades used in the manufacture of stock dimension lumber materials are not terribly wide to start with. Making improvements to stock yield by reducing the saw's cutting width - kerf - will require considerable thought, planning and perhaps accounting for some cost factors not easily seen or calculated before the fact.
Saw kerf, the cutting width of the teeth, is an engineering design element based on and arrived at from several factors:
- the thickness of the tool plate,
- the number of teeth present,
- the size and shape of the gullett spaces,
- the intended function/purpose of the tool,
- the horsepower required in the machining operation, and
- the mechanical properties of the machine where used.
For instance, the use of "more narrow kerf" circular saws in a rough-mill operation can have a twofold benefit. The cutting process will require less horsepower and there will be an increase of stock yield, if this is carefully planned for. Calculating cost savings or profitability increases by way of stock-yield improvements must rely on real-cost indicies, with consideration given to the grade of lumber material involved.
Too often there are unrealistic indicies put into the method of calculating and forecasting the outcomes. Frequently, the errors could relate to something as simple as the grades of lumber involved.
Each mill operation has a moderately different yield formula to pursue. The possible yield improve- ments on gang rip saws are somewhat different from straight line rips, and are different from the yields possible on throughfeed moulders. In each instance, there are applicable fudge-factor multipliers that will provide approximate yield figures that are attainable.
Remember these numbers are approximate. Throughout all rough mill operations, the lumber grade and application dependent factoring varies from about 0.5 percent to 0.8 percent. This means that if the first run numbers indicate a possible 2.8 percent improvement, a more likely outcome would be about 2 percent. This is a very worthwhile improvement, if not overwhelmed by the costs of implementing the new tooling.
Saw kerf is still one of the machining factors where we can make improvements, if we carefully examine all of the elements involved. The operational features of circular saw blades that we can examine include:
- improved finish quality,
- increased feed speed,
- longer sharpening life times,
- reduced horsepower consumption and
- greater stock yields.
Updated: Nov 18, 2009
This article appeared in FDM, December 1999. ©Copyright 2013, All Rights Reserved.