The recent thread started by Randy Anderson regarding the measurement of grinding angle got me thinking about what we mean by grinding angle and its relationship to the actual cutting angle of the tip of the tool when a wheel grinder is used. (If flat belt grinder is used, both angles are the same.) In either case, the grinding angle usually is measured by laying one arm of a protractor across the ground face and the other leg parallel to the shaft of the tool. For or a wheel grinder, this angle is always larger that the resultant cutting angle –the angle between the top of the arc and the top of the tool. The latter angle is what determines the performance of the tool but is difficult to measure directly. The difference between these two angles depends on the size of the grinding wheel, the thickness of the tool being ground, and the grinding angle.
The engineer in me insisted that I calculate how big is the difference between the grinding angle, as defined above, and the cutting angle. It turns that for most cases of interest the difference is minor, so we can all heave a sigh of relief. Here are some typical results for an 8-inch grinder for two values of tool thickness:
Grind**Cut Angle*Cut Angle
Angle**¼" Thick**½ Thick
*30°****29.1°****28.2°
*40°****38.8°****37.7°
*55°****53.5°****52.1°
*60°****58.45°***56.9°
A further point—If the heel of the tool is ground off, then tool thickness for purposes of these calculations is the distance down from the top of the tool to the point where the heel grinding intersects the arc produced by the sharpening.
(Am I the only one who lies awake at night solving trigonometry problems?)
The engineer in me insisted that I calculate how big is the difference between the grinding angle, as defined above, and the cutting angle. It turns that for most cases of interest the difference is minor, so we can all heave a sigh of relief. Here are some typical results for an 8-inch grinder for two values of tool thickness:
Grind**Cut Angle*Cut Angle
Angle**¼" Thick**½ Thick
*30°****29.1°****28.2°
*40°****38.8°****37.7°
*55°****53.5°****52.1°
*60°****58.45°***56.9°
A further point—If the heel of the tool is ground off, then tool thickness for purposes of these calculations is the distance down from the top of the tool to the point where the heel grinding intersects the arc produced by the sharpening.
(Am I the only one who lies awake at night solving trigonometry problems?)