Dear Doc: At a trade show, a company displayed a grinding wheel with slots, where coolant is poured into the center of the wheel and then ejected into the grinding zone. What's your take on this design?

The Doc Replies: Here's how this gizmo works: Coolant is poured at low velocity into a recess around the rim of the wheel, centrifugally accelerated by the wheel and ejected everywhere through slots around the wheel perimeter. And everywhere includes a small portion—around 2 percent on a good day—that's the grinding zone. But this technology is nothing new, having been developed in the 1970s for creep-feed operations.

I've visited hundreds of grinding shops on five continents and have never seen one of these gizmos in actual production use. Maybe I'm just going to the wrong places. Or maybe they look pretty in a display case, but they're not doing the hard work on the shop floor.

Why is that? There are several reasons. First, the spindle motor has to accelerate the coolant to the wheel speed, which requires a lot of power. Second, as previously noted, the coolant is ejected not just at the grinding zone, but along the entire wheel circumference. Third, the coolant is ejected from the slots, but not necessarily where it's needed most, which is the unslotted regions where the abrasive meets the workpiece. Fourth, all that coolant flying out means that if there is any coolant coming from a main nozzle, it gets deflected. Fifth, the wheel is expensive. Sixth … well, let's stop there.

Whenever a wheel salesman pitches me about some new grinding technology, my first question is always: Can you give me some hard science behind the technology and some verified data from case studies? The answer is usually vague, including references to high quality and state-of-the-art technology, with anecdotes about some company in some distant land that saw cycle times drop drastically. But I seldom get real, hard science.

Keep in mind we're talking about a coolant gizmo, not just slots in the wheel. Slots alone, when used with a high-velocity main nozzle, can reduce grinding temperatures when creep-feed grinding.

Dear Doc: I grind camshafts and am always battling burn. To assess the burn, I nital-etch some workpieces but it is messy. Is the Barkhausen Noise method an option?

The Doc Replies: Nital etching, a process where the specimen is dipped in a bath of nitric acid and the color on the workpiece surface changes from gray to white in the regions that have suffered rehardening burn, is indeed very messy.

Barkhausen Noise has come a long way in the past 15 years and is now a robust, albeit tricky, method for assessing grinding burn. If you're looking for a plug-and-play measurement device, where you buy the device, remove it from the box, plug it in, stick the Barkhausen probe on the workpiece and get an immediate answer, then don't bother. It won't work for you.

But if you're willing to take the time—months in some cases—to understand the signal, how it increases with residual tensile stresses and softening, how it can suddenly drop in the regions of the workpiece that suffer from rehardening burn, how different materials impact it and how to establish a baseline signal and then make comparisons from that, then the method could work well for you. Lots of cam producers are generating good results with it every day. CTE