A pump drill is an ancient tool traditionally used to generate friction heat for starting fires, as well as for boring holes. The principle of a pump drill’s operation is easy to grasp, but hard to explain. It’s similar to the button spinner or whirligig, in which rotational momentum is built and maintained by repeated twisting and untwisting of a cord.
I first got interested in pump drills after reading a 1993 article by Anthony Follari, originally published in the Bulletin of Primitive Technology #6, about the design, construction, tuning, and operation of fieldcraft pump drills for fire-making and hole-boring. That article, and many other fascinating pieces from the Society of Primitive Technology, has been republished in an outstanding compilation called Primitive Technology: A Book of Earth Skills. After reading it, I got interested in the idea of a “modern” pump drill, operating on the same principle as the ancient tool but manufactured using industrial-age materials instead of wood, stone, and bone.
A bit of research revealed that, in fact, small pump drills were manufactured and regularly used up until the early 20th century, at least, primarily by metalworkers—silversmiths, jewelers, and clock- and watch-makers—to bore small holes in homogeneous materials like brass, precious metals, and stone. The reciprocating action of a pump drill is most efficient when the bit can cut on both clockwise and counterclockwise strokes, and modern “twist” drill bits are designed to cut in one direction only. Therefore jewelers’ pump drills were commonly fit with simple flat drills as illustrated above and to right. A bud bur or other achiral grinding tool would’ve been another option.
I knew from reading around the web (e.g. on Treewright’s blog) that a few of these 100-year old tools were still floating around the antiques market, so I set up an eBay auto-search for “pump drill” to see what surfaced. That was late 2009, as I recall. It took awhile, but, sure enough, about three months back that search turned up the specimen shown above, which I snagged for just under $40 including shipping. It’s 12-1/4″ long, from the end of the shaft to the nose of the collet, and 9-3/8″ wide across the handle. The flywheel is brass, 2″ in diameter, and the whole tool weighs a bit under half a pound (210g).
When it arrived, the pump drill was fit with a piece of flat braided cord that, I suspect, had been part of an old shoelace. The possibility that this was the original cordage seemed remote, at best, so I didn’t hesitate very long before cutting it off and, following the example of Practical Machinist forum member gwilson, replacing it with a piece of 1/8″ leather cord about 20″ long.
As received, the collet jaws did not tighten noticeably, even when the cap was tightened down as far as it would go. I solved this problem by dismantling the chuck and shimming the collet forward, just a bit, with a small piece of plastic cut from an old plastic swipe card. I just dropped this into the bottom of the receiving sleeve and reassembled the chuck. Thus modified, it accepts round stock between about 1/16″ and 1/8″ in diameter.
One of the advantages of using a pump drill over a bow drill, brace, or other manual boring tool is that a skilled user can operate a small pump drill with one hand, while using the other to position and steady the work. In the embedded video, YouTube user zeiglerr demonstrates that trick. Though the tool he’s using is an antique, like mine, he points out that Swiss watchmaker supply firm Bergeon & Cie offered a very similar model (#1312-30) in their catalog (PDF) as recently as 2002!
Using my pump drill, it takes about 30 seconds to drill a 1/16″ hole in 1/16″ sheet brass, using a modern twist bit made of high speed steel. I start by marking the drilling location lightly with a center punch and applying a drop of mineral oil to lubricate the cut. I also lubricated the shaft of the drill, the first time I used it, by rubbing it a couple times across a bar of soap. Friction is the great enemy when operating a pump drill, because if the bit binds you lose all the momentum in the flywheel and you have to rewind the cord and pump it up to speed again.
I experimented with making my own flat drills by cutting off and filing the tips of small flat-blade screwdrivers, and was able to actually bore a couple holes with these. Twist drills of equivalent diameters, however, were always cleaner and faster, in my hands, even though they theoretically only cut on a 50% duty cycle. I haven’t tried it with a bur, yet, but I think that’s next on the list.