There has been quite a bit of discussion lately about the choice of grinders for sharpening woodturning tools. One candidate favored by several, including myself, is the Rikon 1/2 HP low-speed grinder. Others are doubtful that it has enough power. I would like to explore the pros and cons on a technical basis. If the concern is that the 1/2 HP Rikon grinder will bog down under heavy tool pressure, then I offer these facts. First, the 1/2 HP low-speeed grinder will produce the same maximum torque as a 1 HP high-speed grinder. Second, the tool pressure required to stall either is far far greater than one would ever use for tool sharpening or even rough shaping.
This latter statement is based on actual measurement of the performance of my Rikon 1/2 HP grinder with an 80 grit CBN wheel. I have measuring equipment that can measure the actual input watts to a motor for any given load. From the input wattage one can calculate the output horsepower, ( Actually, this number will be a few percent larger than the actual output power, because of heat losses in the motor.)
I took a a very heavy round nose scraper and applied it to the grinder and noted the force and the power input in the motor as I pressed the scraper into the wheel. At a tool pressure of 10 pounds, the motor was developing only 0.34 horsepower, about two thirds of the potential horsepower! In the few seconds that it took to make the measurement, the scraper was badly defaced.
I believe that the normal pressure used to sharpen turning tools is measured in ounces, not pounds. I did not attempt to determine the ultimate pressure required to stall the motor, because I did not want to sacrifice any of my turning tools nor the CBN wheel to the extreme pressure it would require.
One could argue, based on these results, that a low-speed grinder of 0.25 horsepower would we adequate for this purpose. However, the start-up time with massive CBN wheels probably would be a problem.
This latter statement is based on actual measurement of the performance of my Rikon 1/2 HP grinder with an 80 grit CBN wheel. I have measuring equipment that can measure the actual input watts to a motor for any given load. From the input wattage one can calculate the output horsepower, ( Actually, this number will be a few percent larger than the actual output power, because of heat losses in the motor.)
I took a a very heavy round nose scraper and applied it to the grinder and noted the force and the power input in the motor as I pressed the scraper into the wheel. At a tool pressure of 10 pounds, the motor was developing only 0.34 horsepower, about two thirds of the potential horsepower! In the few seconds that it took to make the measurement, the scraper was badly defaced.
I believe that the normal pressure used to sharpen turning tools is measured in ounces, not pounds. I did not attempt to determine the ultimate pressure required to stall the motor, because I did not want to sacrifice any of my turning tools nor the CBN wheel to the extreme pressure it would require.
One could argue, based on these results, that a low-speed grinder of 0.25 horsepower would we adequate for this purpose. However, the start-up time with massive CBN wheels probably would be a problem.