Batman's Grinder Use is Unsafe

Consider the following scene from Batman Begins, where Bruce Wayne, preparing for his new life as the Dark Knight, sharpens his bat-shaped throwing blades on an ordinary bench grinder as might be found in workshops and indeed, suburban garages around the world. Unlike much of what makes Bruce Wayne Batman—his bat-vehicles, his supercomputers, his Tibetan ninja training—this is low-tech blue-collar stuff, accessible to the home DIYer and therefore dangerous to the home DIYer, if the movie's depiction of grinder use should be unsafe. And it is.

Bruce Wayne attempts a DIY project

First, the good: he's wearing goggles. There's no debate here, he's doing the right thing and so should you. The only possible criticism is that, given the serious possibility of a grinding wheel shattering altogether, Mr. Wayne might want to think about using a full face shield instead.

Second, the debatable: he's wearing leather gloves. The usual thing to do when questions of this sort arise is to seek out the oldest, most grizzled veterans and listen closely to their horror stories. In this case, however, the veterans disagree somewhat on the use of gloves with grinders; one camp holds that they're useful for preventing surface damage to your hands should they contact the wheel, the other camp (more numerous) maintains that they're unsafe around rotating machinery generally because they can get caught up and pull your hands in, where your hands will surely be mangled. I agree with the no-gloves crowd that losing skin beats structural damage, so I don't wear gloves. You take your own risks if you decide to do otherwise but at least ensure that your gloves are close-fitting.

Third, the bad: he has the tool rest adjusted way too far from the grinding wheel. The gap looks like it's almost half an inch!

More dangerous than Arkham Asylum

So why is this practice dangerous? Observe that the forward face of the wheel moves down when the grinder is powered and therefore applies a downward force on the edge of the workpiece. The blade is a lever, and the fulcrum is the corner of the tool rest. If the gap is large, so is the length of the lever, and it will be that much easier for the wheel to grab the blade and tilt it down. This means that Wayne's hands will be pulled, possibly violently, up and towards the grinding wheel (the sharp weapon he's working on doesn't make things safer either, obviously).

Even worse, the gap is larger than the thickness of the blade itself, so when this chain of events occurs the grinder will pull it down into the gap, with the blade ending up almost vertical. Probably this will stall the motor. Probably it will damage the workpiece, the wheel and Wayne's hands before it does. The man is used to pain, no doubt, but Gotham can't wait for its defender to recuperate from a bone-headed mistake like this!

Notice also how delicately he holds the part he's grinding, by the corners; this is asking for trouble as, given that he's set up the grinder with such a large gap, the only way to prevent the bloody scenario detailed above is to firmly press the workpiece onto the tool rest to counteract the action of the lever. But really, Mr. Wayne and everybody else should just set the machine up correctly, by adjusting the position of the tool rest until the gap is less than 1/8 inch and ideally even closer than this, almost touching, especially if the thing being ground is itself thin.

Lucius Fox would never set up a grinder like that; he's a veteran tool-user himself and still has all his fingers. Take a lesson from him and be safe!

Count 'em.

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