Speaking for myself, when I first started, I thought that there could never be a reason that anyone would every need more than a 1hp grinder...... as my grinding skills improved, I found that it became common for me either stall the motor or trip a breaker, even if the 1hp was wired for 220v..... so eventually I went to a 2hp.... thinking the same thing...that there was no way in the world that I would ever need anything more......but again, after an even shorter time frame, I once again was back to stalling the grinder or tripping breakers.
So...... then I went to 3hp motors..... and so far, have only had rare instances where I've slowed the grinder (what I've found is that with a 3hp motor, the belt slips before the motor stalls.....as long as you have a solid drive wheel.) I have a rubber coated drive wheel on my 3hp original KMG, with a 10" serrated wheel for profiling and other heavy tasks, and if I really lean into it, I can drag the motor down a bit....but after learning the sound, it's just a reaction now, to let up when I hear that sound.
Some might remember the one whom many consider the greatest blade grinder ever.... the late
Bob Engnath. The last time I ever visited his shop before he passed, there were custom made grinders, from 2x72" to belt sizes I never imagined. The smallest motor on any of his grinders was 5hp (he had 2 Older Burr Kings, each with 5hp motors)..... all the way up to a 10hp on a machine that I believe was a 3 or 3 1/2" x 132". Bob was the best, and the fastest blade grinder I have ever seen, or likely ever will. We're talking about a guy who could literally take a profiled katana blank, and have it ready to heat treat in a matter of
MINUTES. When he talked about grinders, he would always say.... "There is no substitute for Horsepower when it comes to grinding." While I know it's always best to slow down, and take your time when grinding..... when you have those kind of grinding skills..... smaller HP motors only hold you back. I know there are times with my original KMG and that big steel hubbed 10" serrated wheel, that I wish I had more "ponies".
