Return of the Mortise Machine
We first showed you the Miller mortise-joint machine in the December 1997 issue. Back then, we left you with a question: How does it work? A number of you took up the challenge to explain this thing.
Most speculation about how the Miller machine works centered on those mysterious, toothed rods. Some correspondents wondered if the machine in the photograph had been dismantled, and then reassembled incorrectly. "Reverse the rods!" they implored. This way, the rods' teeth would face outward and could grip against the adjustable blocks, helping to advance the cutter into the work.
That this machine could have been improperly assembled by some previous owner seemed entirely plausible. But then we heard from Loring McKenzie of Logansport, Indiana.
A tool collector, Loring sent photos of several mortise machines he owns, including a Miller. Close inspection of the photo of his Miller machine showed the rod teeth facing inward. We took this as evidence (though it's hardly conclusive) that the rods were installed correctly on Dick Gowen's machine that we showed.
Loring figures that the Miller machine was intended to finish a mortise first roughed out by drilling. Several other readers focused on that idea of drilling first, too. Some held that the entire mortise would be drilled out, and then cleaned up with the machine. Others leaned toward drilling two pilot holes, one at each end of the mortise. The more we thought about it, the more we came to accept the pilot-hole theory of operation. It was best expressed by Tom Oertling, a Galveston, Texas, woodworker trained in archaeology.
"I believe that the ends of the mortise were defined by two holes drilled straight down to the depth (and maybe plus a little) of the mortise," he wrote. The rods would then extend into the pilot holes, and the adjustable blocks would be adjusted to press them against the sides of the holes.
"Note that the ratchets are cut so that the rod will move down in the hole, but will bite (into the end-grain wood) if it is pulled up," he added.
Swinging the handle to the right extends the right rod farther into its hole. As the handle moves leftward, the right rod, its teeth pressed against the side of the hole, resists pulling up. At the same time, the left rod advances farther into its hole. This action would advance the handle/cutter assembly, by Tom's reckoning.
"This machine would probably not have left a very clean mortise. No doubt some chisel work was necessary to clean it out," he said.
We'll let that explanation stand for now. But someday, someone will happen across a yellowed instruction booklet for Miller's Patented Mortising Machine. Only then will we know for sure just how this thing is supposed to work.
Machine coutesy of Dick Gowen, Aurora, Nebraska; Photograph: Hetherington Photography