The cutting edges of all tools need to be kept sharp. When new, or newly sharpened, the leading edge of a cutting tool knife will have a somewhat irregular surface measuring from 3 to 5 microns across. (This figure is dependent upon the composition of the knife alloy and grinding method employed.)
It's important to understand how cutting tools are sharpened. For instance, saw blades are sharpened by grinding both the face and top edges of the teeth; most router tools and tipped shaper/moulder cutters are sharpened only on the face surface. The longer you run a tool between sharpenings, the more material will have to be removed to return it to sharpness. Therefore, how long we run a tool between sharpenings can dramatically affect its useful life.
There are unfortunately no specific guidelines nor inclusive methods yet devised to help us forecast what a "normal sharpening life" for each tool and tool type should be. But by following a few basic rules and observations, it is possible to develop a workable means to estimate how long most of our cutting tools will operate before becoming dulled.
First we can list some of the common sense rules of tool performance to be aware of:
- Feed speed has more effect on the tools' useful life than any other operating parameter.
- Get to know many of the properties of the materials being cut, regardless if it's a natural or man-made material.
- Materials with a higher moisture content cut hotter and shorten tool wear life.
- All adhesives and many laminating materials are very abrasive and can dramatically reduce cutting tool wear life.
- Man-made panel materials can vary in composition, affecting tool wear.
- As tools dull, the sounds created change dramatically, the tools run hotter, and they vibrate more.
Monitoring tool wear requires that we record and control the variables present, such as the tools' operating conditions, including RPM and feed speed. Further, we need to document an accurate description of the material being machined. With such information in hand, forecasting tool wear can proceed over time as more materials and machining processes are examined.
There is a shorter and more accurate means to measure tool sharpness while tools are at work. The amperage load on machine motors relates directly to the amount of energy needed in the machining task. As tools dull, the amperage load will increase, but not in a logical arithmetic progression. Most tools incur 80 percent of their relative wear in the first 20 percent of normal run time, with the last portion of the sharpening life a longer, slower progression.
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