Testing cutoff wheels

Dear Doc: I manufacture cutoff wheels and would like to implement some sort of testing program to evaluate them. Can I do this inexpensively? I’m not looking for anything fancy, just a quick method to determine wheel performance.

The Doc Replies: The minimum you need to measure is grinding power and wheel wear. Connect a genuine power meter—not an ammeter—to the grinding wheel motor and measure power during grinding. Grind several test specimens and measure wheel diameter before and after. Calculate the wheel-wear factor (1/G-ratio) by dividing the volume of wheel lost by the volume of material ground. 

Courtesy of J. Badger

When testing cutoff wheels, you’re looking for “outliers,” wheels that fall below the curve. These are wheels that, for a given grinding power, wear less.

In a perfect world, you’d have wheels that generate little power (and heat) and wear little. In the real world, “harder” wheels wear less but generate more heat, whereas “softer” wheels generate less power but wear more, meaning they’re freer cutting. This is shown by the curve in the figure.

Start plotting tests results and you’ll produce a similar curve. What you’re looking for is the “outliers,” the wheels that lie below the curve. For example, wheels that wear less for a given grinding power. An example is wheel 5. 

Bad wheels are those that lie above the curve, or wheels that wear more for a given grinding power. An example is wheel 6.

But even for those wheels on the curve, you can choose a wheel based on a customer’s needs. If the customer is having burn problems but isn’t concerned about wheel wear, choose a wheel on the curve that lies toward the left. Examples include wheels 1 and 3. If your customer just wants wheels that last a long time and doesn’t mind lots of heat, choose a wheel on the curve that lies toward the right. Examples include wheels 8 and 9.

Keep in mind these are the bare-minimum requirements for testing and analysis. Once you start testing and processing the results, things get more complicated. Some wheels will go through oscillations of dulling and self-sharpening, while others will consistently self-sharpen and give steady power. Some wheels will operate well under certain speeds and feeds and worse under others. Some wheels will grind certain materials effectively but not others.

I’ve set up several wheel manufacturers with this test program. The smart ones test before approaching a customer. They determine what material the customer is grinding and the grinding speeds and feeds. Wheel manufacturers then replicate these conditions when testing and find a wheel that works well under the customer’s conditions. 

Then, when manufacturers visit customers with wheels in hand, they are not just shooting from the hip, hoping their products work well. They have a proven cutoff wheel. As a result, the customers are much more likely to succeed with the new wheel.