Determining Saw Blade Quality from Chip Size
How tools form chips during the cutting process is usually of more importance to the Toolmaker / designer than to the woodworker.
Woodworkers most often simply check sawdust and chip size visually as a gauge of tool performance, and that is usually an accurate estimation based on the history of a particular tool cutting a specific material-with some precautions.
For instance, the same saw blade used to cut several different materials in differing orientations will produce sawdust and chips that appear radically different from one another.
The list of conditions that affect chip size would include:
1. The make up of the material-solid natural wood, plywood, particleboard, hardboard, and so on;
2. Orientation of the cutting process-ripping, cross cutting, mitering, jointing, etc.;
3. Relative strength of the material-grain makeup (if present), density, hardness, and the other measures of strength;
4. Moisture content of the material;
5. Condition of the tool-sharpness, balance, and concentricity;
6. Tool design features-cutting and relief angles, gullet size, and shape and number of cutting teeth/knives;
7. Process characteristics-feed speed, rim speed, etc.;
8. Machine characteristics-vibration, tool or stock clamping and holding method;
9. Conditions of the process-adequate methods and means to remove the waste offal, chips, and sawdust;
10. Climatic conditions-humidity, heat, and barometric pressure can affect tool performance.
From this list, we can see that the appearance of sawdust and chips is the result of many factors. Most often, though, tool sharpness is identified as the primary reason why sawdust looks as it does, and that may be only partially true. For instance, if a perfectly sharp, new saw blade is placed in a condition where there is no adequate means to remove the waste chips during cutting, the chips could stay in the area and be re-cut repeatedly into dust before being pushed away from the tool. Another instance may be when a saw blade with a large number of teeth is fed too quickly or too slowly for the intended design or function. Either condition will have dramatic effects on the performance of the tool.
All chip formation is a stress reaction process, that is, the cutting tool has to overcome the strength of the material being cut and remove the waste offal. This is, again, not as simple as it might appear.
Tags: chip size, cutting tools, tool performance
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