I just added a few more 18th century gunsmithing tools to my tool kit. One is a pristine early screw plate, probably from the late 18th century or early 19th century. I don’t think this thing has ever been used. It appears to still have the temper colors on it. At least it did, until I started using it ;).
The other tool is a square shank circle cutter for use with a brace. However, I didn’t buy it as a circle cutter. I thought that with the addition of an appropriately sized dowel on the center point as a pilot, I could use it to cut circles on the muzzles of barrels. Southern longrifles were often decorated on the muzzle with engraved circles, and stamped circles and stars. I had been meaning to make one as most of the ones in period gunmakers’ tool boxes were apparently homemade. However, I saw this thing on ebay for less than $20. I snapped it up as quick as I could. I had never seen one before and didn’t know any such thing existed as a commercial product.
Below are a couple photos showing the screw plate with a few modern screws that fit that plate. I also measured the root diameter of the holes in the screw plate using wire number twist drills. The fit of the drills is between .001″-.003″. I have also shown the data associated with using #4 and #6 machine screw blanks to cut screws using the screw plate. I will continue working to develop a set of tap drills, square reamers, taps, and screw mills from this screw plate to cut the screws required of a flintlock.
I have learned the hard way that it is very easy to twist off a screw blank in this screw plate and very hard to get out the broken bit. I was able to drill out and pick out most of the metal, but some was stuck down in a thread. It is hard to clean out a 4-48 thread. I made a tap, using the larger hole, with a screw blank which I tapered and case hardened. If I was planning to use it more than once, I would have forged it out of a piece of w-1, but using the screw blank was quick and easy. It worked just fine.
Anyway, I have learned that the screw blank needs to be smaller than I would normally think due to the expansion from swaging; and that I need to be very careful about the pressure I apply.
It is starting to look like a blank that fits in the next hole up is about the right diameter for swaging the thread in the chosen threaded hole. That next hole up also looks to be the correct size for the tap drill/reamer for the selected screw or tap hole. Just as a reminder, the smaller of the pair (connected by the diagonal line) of holes is for the screw and the larger is for the tap.