The boring parts of drills are not unfrequently found. The most ancient illustrations known to me of drills driven by thongs are in the work by Vidus Vidius (Chirurgia e Graeco in Lat. Conversa, V. Vidio. Florent. interprete c. nonn. eiusd. commentariis. Lutec. Paris., 1544).
Vidius shows three arrangements for driving these drills with thongs: the first method consists simply of a thong attached to the shaft of the drill ([Pl. XLII, fig. 4]); the second consists of a bow with the string of the bow wound once round the shaft ([Pl. XLII, fig. 5]); and the third consists of a crosspiece with a hole in the centre of it through which the shaft passes, and having strings from the end of the crosspiece to the top of the shaft ([Pl. XLII, fig. 3]). Primitive arrangements truly, yet all three methods of producing rotary motion are to be seen in use at the present day, and be it known that some of the most delicate boring performed by the hand of man at the present day is done with drills turned by the thong stretched across a bow. The latest developments in mechanical devices for drilling have failed to displace thong-driven drills for boring the holes in which the wheel spindles of the best hand-made chronometers move, and the spindles themselves are turned in chucks rotated not by belts in continuous rotary motion, but in alternating motion by means of a thong stretched across a bow. A bow of cane with a strong but fine thread, one turn of which is taken round the drill, is drawn backwards and forwards and rotates the drill with marvellous rapidity and accuracy. The bows used by watchmakers average about a foot along the string. Similar drills are used by engineers in turning out small work. The form with the crosspiece may be seen in use by travelling crockery menders, who drill holes in broken pottery and clamp the pieces with rivets. A turn or two of the string is made round the shaft, and the point of the drill being adjusted on the spot to be bored the crosspiece is gently pressed down by the first and third fingers, causing the shaft to rotate. When the thong has nearly uncoiled itself the pressure is slightly removed, the momentum causes the shaft to overrun and coil the thong in the opposite direction to which it originally was. The crosspiece is again depressed and the alternating rotation goes on without intermission, and the drill bores through the pottery. The travelling crockery mender is, in the northern towns of England, not an unusual sight squatting at work on the kerb. On the continent the ‘Rastelbinder’ is a regular domestic institution. Not only crockery but glass is readily drilled by these means, and one who has seen the rapidity with which these drills rotate can readily understand the necessity for the advice given both by Hippocrates and Celsus to frequently remove the drill and dip it in cold water, in case sufficient heat be generated by the friction to cause subsequent exfoliation of the neighbouring bone.
The remaining method of producing rotation by means of a string fixed to the shaft can be seen in use by boatmen when clearing water out of a boat with a mop, The mop is laid over the side of the boat. A few turns of a rope fixed to the shaft are made round it and the rope being pulled the shaft rotates. The momentum generated causes the shaft to overrun and the rope to coil itself in the reverse way to the original. This is repeated till the speed generated causes the water to fly off the mop by centrifugal motion.
The fire drill of the ancient Egyptians was turned by a bow, and it is interesting in connexion with the advice of Hippocrates to avoid generating too much heat in drilling the skull, and also because it helps to explain the construction of the instruments of Vidius. A sketch of an ancient fire drill found by Flinders Petrie (Ten Years Digging in Egypt) shows that the head of the drill was separate and the points were also removable.
Drill with Guard.
Greek, τρύπανον ἀβάπτιστον; Latin, terebra abaptista.
This is the second variety of drills described by Celsus. It had a collar which prevented it from sinking beyond a certain depth, so that in excising a piece of bone from the skull, which was the object for which it was used, there was little danger of its doing injury to the brain or its membranes:
Terebrarum autem duo genera sunt; alterum simile ei quo fabri utuntur; alterum capituli longioris, quod ab acuto mucrone incipit, deinde subito latius fit; atque iterum ab alio principio paulo minus quam aequaliter sursum procedit (VIII. iii).
Further on in the same passage Celsus states that they were to be frequently removed and dipped in water lest too great heat should be generated, so that they were evidently driven at a rapid rate with a thong like the other drills. They are not mentioned by Hippocrates, but Galen (x. 445) describes them:
‘In order to make less chance of error they have invented drills called abaptista (ἀβάπτιστα τρύπανα), which have a circular border a little above the sharp point of the drill. It is best to have several for every thickness of the calvarium; for thicker bone longer are required, for thinner bone shorter.’