Deep hole drilling or How to keep it straight.
Usually it works like this: for small craft in boring the shaft
wood it can be made in two pieces if wide enough. The top and bottom are given a saw cut dead on center and two other cuts just far enough
inboard from the outside.
Splines of a soft wood will be inserted into the two outboard cuts.
The center one is for use as a guide. The pieces are assembled with the spines set in some sort of long lasting flexible goo or red lead putty.
The shaft wood is bolted to the rest of the deadwood and a regular metal twist
bit with its point ground for wood cutting is used to bore into that center saw cut for the full depth of the bit say 4". Or a Jennings type with one side of the threaded tip( worm) ground flat so there is less chance of the worm wandering off course, welded on a long rod can be used to follow the cut.
Then a 'barefoot ships auger' is used to finish the job. With the saw cut being dead on and the twist bit following the saw cut and the barefoot auger following the pilot hole of the twist bit it bores a nice clean dead on hole. In small craft with a solid shaft log it is similar but done with a jig using a batten to establish the line of boring on the side of the deadwood. With careful eyeballing the pilot hole is drilled and then finished
to the full depth as described above.
On big craft a carefully aligned jig usually 1/3 again as long as the hole to be bored is set up using lines drawn on the outside of the
keel/deadwood assembly. It is a very tricky and time consuming operation for if off just a small amount the engine alignment with the shaft coupling will be out of alignment enough to cause severe vibration and premature wear on the machine parts affected. When all is lined up the boring can begin.
First that all important pilot hole is drilled. The pilot hole again determines the accuracy of what follows. Using barefoot augers of the same diameter with successively longer welded shaft extensions the initial hole is drilled through the wood from outside in.
To get the final size bore for the shaft liner a 'boring bar' similar to what a machinist would use in a lathe, is used to expand the hole to proper dimension. The bar was usually a piece of propeller shafting with the ends modified.
One end had the slot for the cutter holder milled in it and the opposite end had 3 milled flats to fit in a Jacobs Chuck.
When boring for drifts or bolts in timbers it was not so critical to pilot bore to start the barefoot auger. In fact a sharp rap with the tips of the ripping claws of a hammer would create enough of a bite for the cutter end of the barefoot auger to be able to start boring. A more precise mark could be made bye cutting an X on the location with the butt chisel carried in sheath in the pocket of the shipwright's overalls.
Sometimes the cutting edge was dipped in a can of grease or tallow to make the boring go a bit easier and would be renewed whenever the auger was withdrawn to clear the chips.
It is a tiresome job deep boring with the barefoot augers. They have to be withdrawn regularly to clear the chips that build up in the hole behind them or else that bit can snap deep in the hole and then, 'Oh Boy, Katie bar the door!', for there will be hell to pay to fix that mess.