November 12, 2018
A variable speed grinder is a valuable tool to have for surface preparation on curbs and vertical surfaces, as well as for other detail work. Operating a 4” or 5” grinder at lower rpm speeds will provide an operator with better control that can help to reduce the chance for deep and undesired grinder swirl marks as well as reduce the chance of damage to fixtures and frames.
Figure 1: Hand grinder with built in variable speed selector.
Figure 2: 15 AMP Inline router speed controller, zero to full rpm control.
Any single speed grinders can be converted to a variable speed grinder by adding a 15 AMP or 20 AMP inline speed controller made for router use. Decent quality, 15 AMP units run about $30 to $60 on the internet, and will allow for zero to full rpm control with most 4” to 5” hand grinders.
A 15 AMP inline router speed controller that I recently tested worked well with two brands of hand grinders used. My only complaint was that the two hand grinders were low torque units to begin with, and operating at slow speeds of 500rpm to 1000rpm greatly highlighted how low of torque these two hand grinders were.