Ready for use. The drive pegs are engaged with the third ring out from the centre. The knurled locking wheel is coaxial with the drive wheel, and nearest the camera.
The distinguishing feature of a breast drill is the breast plate at the opposite end from the chuck: the idea is that you can lean on the plate while guiding the drill with one hand and cranking it with the other. They are normally quite big and heavy: similar to, but a good deal more substantial than, the ordinary sort of bevel-drive hand drill sometimes described as the egg-beater type. But this one doesn't use a conventional bevel gear, and has four speeds. Even two-speed breast drills are unusual: this is the only four-speed design I know.
Upside-down. You can see the two holes on the crank, one lined up with its locking hole on the drive wheel, and the other of unknown use (see below).
The way it works is ingenious. The drive plate replaces the big bevel gear, the one attached to the crank handle. It is perforated with four concentric rings of holes. Any of these four circles can be engaged with a sliding peg-wheel on the square drive shaft of the drill. To change speed, you slack off the big drive plate via a captive knurled wheel on the axis of the drive wheel. This allows the drive wheel to be moved outwards so that it no longer engages with the pegs. You can then slide the peg wheel up or down until it lines up with another set of holes. Finally, re-tighten the big drive plate to re-engage the pegs.
Drive pegs aligned with outermost circle
Now, the very idea of a variable-speed hand drill seems a little odd at first. Why can't you just wind the crank faster or slower? Well, you can, of course, but it makes more sense when you think of it as a variable-torque drill. On the outside ring, each turn of the crank gives just over four turns of the chuck. On the innermost ring, it gives approximately two. In other words, if you want to drill fast but with reduced torque you use a bigger ring, while for slower drilling with more torque you use a smaller ring. For an obvious illustration of the use of this, think of drilling through a fairly thick sheet of soft alloy, copper or even brass. Often, the drill hangs up just before it is fully through, and it's hard to get enough torque on a hand drill to finish the job. This drill, with its long crank handle and 2:1 gearing, will give you plenty of torque.
Drive pegs aligned with innermost circle. You can also see the grooved edge of the drive wheel (see below).
On the other hand, do you really need four speeds? Wouldn't two be enough? Well, yes, it probably would, which is why two is normally the maximum you find. Another reason is that although changing speeds is easy, it is also quite time-consuming. Yet a third reason is that this design must have been extremely expensive to make, the more so with those rounded-conical pegs and their corresponding rounded-tapered holes.
Close up of drive pegs. The drive wheel is fully slacked off (via the knurled screw on the right) to allow it to be moved outwards.
As I was writing this, I realized that there may be a (possibly optional) part missing. The crank is locked when being turned clockwise but slips when being turned anticlockwise. This is probably achieved by a ball-and-ramp arrangement in the grooved outer edge of the drive plate: the groove is otherwise inexplicable. There is however a non-tapered hole on the drive plate which at the right rotation lines up with a hole on the crank. There is another hole, further out along the crank: both it and the hole in the drive plate may once have been threaded, though wear, rust and dirt make it hard to tell. It would be quite easy to install a small cranked bar with a peg at either end, one to engage with the crank and one to engage with both the crank and the drive plate. This would lock the crank to the drive plate and allow the crank to be turned backwards without slipping. Another possibility is a spring, secured at the outer end, with a peg to drop into the lined-up holes at the inner end: lift it and push it to one side if you don't want the crank locked. I don't know. If I ever see another, I'll check.
The first I saw, at a vide-greniers a few years ago, was 50 euros (call it £40, $70). I admired it but didn't buy it: the owner described it as “very rare” and I saw no reason to argue with him. Then, months later at a vide-greniers in another village, I saw this one for 10 euros, so I bought it. At the same vide-greniers I then saw another, but didn't ask the price. I have not seen another since.
Overall length: approximately 40 cm/16 inches
Length of crank handle, turning axis to turning axis: approximately 15 cm/6 inches
Size of 3-jaw chuck: approximately 1 cm or 3/8 inch
Diameter of drive wheel: approximately 12,5 cm or just under 5 inches
Number of pegs on peg-wheel: 9
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