Belt question?


Well-Known Member
Where do you find, or how do you determine the optimal SFM for a particular belt? I'm asking because I have a smallish drive wheel and am considering getting a larger one, so I'm trying to determine if it would be beneficial or detrimental.
Single speed machine, or variable?

In general, heavier grit belts (36/40/50/60) cut best at higher speeds. As the belt grit becomes finer, slowing the belt down is more efficient and more importantly, generates less heat then running them at a faster speed.
SOME abrasive belt producers will list "optimal" type information on their sites for specific abrasives (usually the structured abrasives), but there are so many types of material being ground, under so many varying circumstances, most will only mention general parameters.

In a single speed grinder application, I would personally prefer a smaller drive wheel to keep speeds down when I get into the finer grit belts. I'd rather have to spend additional time on a heavy grit belt, than burn something up when I get to the finer grit belts (because the belt is moving too fast). Of course that means you're not going to remove material as rapidly with the heavy grits, but just about everything we do in knifemaking is some type of "trade off".

If the machine is variable speed, the main consideration is the HP size motor being used, and the torque it generates......while a larger drive wheel will increase belt speed, torque drops off correspondingly as the drive wheel size increases.

If you're in the early learning stages of grinding, I highly encourage using slower belt speeds.... it not only helps in the learning process, but when a "mistake" is made, it's generally repairable, versus being beyond repair if the same "mistake" were to occur with the belt moving faster.
Fair enough. All of that makes sense.

Currently I have a stepped sheave machine with 4 options. As funds become available a VFD and corresponding motor are near the top of the list.

Currently I have a 2hp motor, 1765 RPM. The drive wheel is 3". With coarse grits it moves material, with great efficiency. Maybe the new drive wheel will have to come with the new motor?

Thank you for the help and information.
I never even thought about "step pulley" systems. I would stick with that until you can fund a VFD. Buying a larger drive wheel when you have the step pulleys is a limited value...I suspect what you'd find is that if you go to a 4" drive with everything else staying the same as you've described, you likely experience "lugging" on the motor at the higher speeds. In my experience, when running a step pulley system, heavy grit belts run/cut best at the NEXT TO FASTEST step on the system. Running them on the fastest pulleys tends to "lug" the motor because of the torque issue, and because of the "V" belt drive, you also loose some power/torque to drive belt slippage.

When/if you do go the VFD route, the 3" drive wheel is going to be about right for a 2hp/VFD setup. I found that a 4" drive wheel required me to go to 3hp motors to compensate for the torque least on my grinders, for the way I grind. (I tend to be pretty aggressive, particularly on the heavy grit belts. :)
Ed Covered this extremely well, Finer Belts, slower is better,
Also the amount of pressure I use with finer belts gets lighter.

Each maker, over time will find their own "Sweet Spot" of speed & pressure for each different material & belt.
All great information, thank you. Like all of you have suggested I too have found that finer grit belts "work" better at lower speeds.
Just today I found a great deal on a 6hp motor that fits the bill perfectly. I realize that's a touch large, but I have the necessary power requirements, and have sourced a VFD that is a good match for that motor. My grinder will need a revamp, and a new drive wheel is going to be required, but it should work great.