Blanchard Grinding

Dear Doc: Are there any hard-and-fast rules for selecting downfeed rates in Blanchard grinding?

The Doc replies: Here’s one rule — downfeed fast enough to keep your wheel sharp, but not so fast that you gobble up your wheel.

Yes, I realize that’s still pretty general, without any specific downfeed rate in inches per minute. But in Blanchard grinding, there are just too many factors to give a specific value. But let’s elaborate, using the machine spindle power as a guide.

Many Blanchards will have some sort of power meter (or amp meter) mounted somewhere. (If not, a well-tuned ear can serve as a quasi power meter.) The figure shows three different feed rate examples: 0.5, 1.0 and 1.5 times some downfeed variables in inches per minute.

If we downfeed too timidly, power will start off low. But the grits in the wheel (or segments) will dull — and power will increase rapidly (red curve). We’ll then suffer a series of “wheel collapses” as the grits dull, shed off and then dull again. If we downfeed reasonably aggressively (blue), power will start off higher (as we are downfeeding faster), but the wheel will self-sharpen. Power will still increase, and we’ll experience some small collapses. But they won’t be dramatic. This is the sweet spot for the operation. Finally, if we downfeed too fast (green), we’ll just eat through our wheel. Granted, power won’t increase. But that’s because the grits are being lost before they have a chance to dull. Moreover, actual material-removal rates will be low (because we’re gobbling up our wheel).