I just finished making a metal bow for my watchmakers type metal bow drill. The bow itself is very simple. Unlike the ones in the period catalogs, it doesn’t have a ratchet mechanism. I was given a old fencing foil with which to make a bow and there just wasn’t enough metal there to support a ratchet. So, I just riveted a little tab on the bottom at the back to which I could attach a bow string. The front was just curled up into a loop for the other end of the bow string. I tried a couple of different string materials but hemp cord seemed to work best. It stretches, but it is easy enough to loosen the knot and tightened it up every once in a while.
The drill itself is also very simple. It is a piece of 3/8″ drill rod with a 1 1/4″ hunk of wrought iron pinned on to the shaft. I turned the spool from the wrought iron right on the shaft. A lantern stock chuck was drilled and filed on the long end of the shaft. It pretty much matches the ones in the period catalogs except they normally had brass spools. I didn’t have a piece of brass big enough, but I did have wrought iron. I figured it was a reasonable period substitution.
So, now I have a fully functional bow drill for drilling metal. I have a hole drilled in a period watchmakers vise to accept the pointed end of the drill shaft. I would hold the work to be drilled in my left hand as I operated the bow with my right hand. That is kind of an awkward arrangement, but that is how it was done. Actually, the watchmakers vise I have came with a hole for a bow drill. I just made it a little bigger.