Drill with Self Centring Chuck - Codex Atlanticus Folio 1089 br

In the Codex Atlanticus Folio 1089 a drilling machine is shown for drilling out logs, possibly for producing water pipes which were needed for distributing drinking water throughout the city. This kind of wooden water pipe was quite common in towns and smaller cities from the 15th to the 17th century.
The technique seemed to be for the tree trunk to be rigidly mounted to a bench and a drill with a very long handle used to drill out the core from the centre of the trunk, it is quite possible to get the drill to follow the centre of the trunk in this manner. The illustrations below show this process. To drill the hole the man needed to push hard on the Auger/drill handle to get the cutting edge to bite into the wood, and at the same time turn the handle to get the Auger/drill to keep cutting. Once a hole was drilled it could be opened out using an Auger /Reamer bit with a hook on the end to enable a rope to be attached to it and weight added to continually pull the Auger through, allowing the man to apply all his energies to turning the Auger handle. The problem was of course that it was a relatively slow process, particularly if drilling into hardwoods.  Research has shown that one man could bore a 5 cm diameter hole through 11.6 metres of pipe per day in alder or elm, but only 1.95 metres per day in oak.
With this in mind then it is clear to see that Leonardo was trying to address the problem on a couple of levels with his self-centring drill. The self-centring chuck allowed the trunk to be held securely in a centrally fixed position relative to the drill as the alignment of the trunk was automatically achieved. The turning of the Drill/Auger bits was to be automated by having the tailstock driven by a belt drive attached to a manually turned Flywheel as seen in some of his other drawings, but not shown in this particular sketch, or indeed turned by a waterwheel. The result of these combined innovations the whole process could be significantly speeded up.
The 3D construction of this machine has been approached in the same way that all the other reconstructions have been and that is,  as a builder of the first prototype. The sketch in itself does not supply sufficient information for a prototype to be built, it needs a more detailed layout of the parts to be made either on paper or as I suspect would be done back then, on the floor with compass scriber and ruler.I have done this using a 3D CAD program, making estimates of the main basic dimensions and then constructing from that detail profiles for all of the parts prior to cutting out from timber. The gears could be a problem as they need very precise laying out to ensure proper engagement, but the skills necessary to make the gears and the screws were available in this period, indeed, Leonardo even had designs for screw-cutting machines capable of cutting the long leadscrews used in the self-centring drill. The difficulties I suspect would be with the sizing and positioning of the gears not the actual making of them, however having said that the ability to build chariot wheels dates back to the ancient Egyptians, so it is entirely possible that the gears could be designed and built.
There are 2 main problems with the design as laid out by Leonardo, so modifications were made to the design to overcome the first but I left the second as drawn originally. The first problem concerns the use of 4 jaws in the self-centring chuck, as shown in the sketches above. Four jaw self-centring only works on perfectly round or perfectly square shapes. The reason is that if not perfect, two opposed jaws will always touch the trunk first and once that occurs all movement stops so the other two jaws clamp on nothing. It's like a four-legged chair on an uneven surface, 2 legs touchdown first and then the chair tilts until to a third leg touches and the 4th is left in fresh air.
Three Jaw chucks, on the other hand, do not have diametrically opposed jaws so the normal gravity will move the trunk to sit on the bottom two jaws and they continue to move laterally across the surface of the trunk until the third jaw engages, then tightening takes place.  For this reason, 3 Jaw self-centring chucks are universally used for general work holding in a lathe and 4 jaw chucks are generally had independently movable jaws.
I have therefore changed the design to use 3 jaw design.
The second problem is that for the drill to be used to make pipes, it needs to be able to drill very deep holes perhaps in the region of two to three meters. To do this there need to be some means of loading heavy trunks into the jaws and some means of supporting the overhanging trunk behind the machine. I have not shown any of that structure as it would be a pure invention on my part and not the purpose of this exercise. This excessive length creates problems elsewhere, the bed of the machine limits the length of the drill that can be used so it will need to have a couple of extension pieces made that can be fitted to the back of the drill when the tailstock reaches the extent of its forwards' motion. The tailstock needs to be withdrawn fully to allow the extensions to be fitted. I have shown Drill and Auger bits common for the period along with a sample of the type of extension required.