Variable speed...

Chris Railey

Chris Railey

Well-Known Member
I am about to order a grinder with variable speed. I have never used. V.S. Grinder before. Can some of you who use V.S. Grinders please give me an idea of when you like to slow your grinder down or find it beneficial to do so. Thanks.
 
I notice that I tend to go very slow. Often in the region of 350 to 650 rpm and for no other reason than that I find I have more control over the grinding process. I do primarily flat grinds and that is what I do.
 
Different belts do their best work at given speeds.

Heavy grits (36-80) are meant to run at higher speeds. Then as you work down through the grits, slower and slower.

I can't give you rpm or sfpm, but when running my machines (all variable) I run 50 grits belts at 75-100% on the controller. 220 belts run at 40-50%, 400s at 30-40%, and 600+ grit at 20-30%.
 
Variable speed is the ONLY way to go. I'm saying this after a couple yr of using a 3 speed pulley setup. A direct drive tends to run smoother. BUT - you asked about the why of slowing grinder speeds. I'll run max speed for profiling and rough bevel grinder with 36 to 60 grit belts. Then with 120 grit slow down some, then with 400 grit range I'll be down to the 1500 SFPM range. Then with anything in the 600 grit range I'll be down to <1,000 SFPM range.

Then when doing final grinds on scales I might be down to the 300 to 500 SFPM range. And when doing sharpening on 2X72 I'll run grinder in reverse and slow down to the 300 SFPM range and even 200 SFPM range for final grits and leather. Also, for working mammoth ivory and MOP you're really going to want slow speeds.

"IF" you have to purchase a motor, a 3 ph motor is about the price as a 1 ph motor, and a NEMA 1 enclosure VFD is less cost than 3 step pulley, jack shaft, and bearings. With filters installed over the air inlets the $70 Chinese VFD is going to last several years.

Ken H>

edit: I see Ed has already posted some of the speeds I mention. BTW, with a 4" drive wheel the rpm is pretty close to SFPM belt speed.
 
The closer I get to finished, the slower I go.
If I have to clean up a plunge line, I will slow it down to barely moving sometimes to get in right where I want it with out messing something else up.
Once I have a blade rough ground, I will slow down to half speed or less and then progressively go slower from there down to 1/3 speed.
Most woods or phenolics will burn at high speed with a small grit. I automatically go half speed or less when working with those.
 
Ok, all of that helps I appreciate all the responses. That gives me a ballpark to work in I will figure the rest out through trial and error. Thanks again. I cannot wait...variable speed AND small wheels, its gonna be a new ballgame.
 
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