Making wood thread taps
I started by making a "jig" to hold the threaded rod for grinding slots in it.
I cut a total of six slots in the threaded rod. I used two hex nuts jammed against each other on the threaded rod to guide how much to turn it by to space the slots. Spacing four slots evenly would have been more tricky unless I found a square nut to fit on the threaded rod (or I suppose, I could have jammed a square piece of wood between the two nuts as a guide)
The metal one works just fine in wood (and metal). Interestingly, the metal tap is slightly bigger than the one I made. When threading holes in metal, the hole needs to be slightly bigger than the bolt or threaded rod that screws into it, or it will get stuck. With wood, having a hole slightly smaller is not a problem because the wood has some flexibility. That's how wood screws engage.
The homemade tap cuts the thread with just the first few turns so it can cut threads closer to the bottom of a blind hole. I could just make another one with no taper at all to cut threads all the way to the bottom of a hole. That's the nice thing about homemade tools — infinitely customizable.
Testing it out. Worked well. Though, in retrospect, I should have cut the flutes slightly larger because they had a tendency to get filled with sawdust. Drilling a larger hole before tapping would also help.
It was easy to screw a threaded rod into the resulting hole just by turning it with my fingers.
I figure this could be a handy alternative to using a machine screw and threaded insert for some adjustment knob or fastening knob on a homemade machine. With so much wood between the threads, it's very unlikely that the threads would wear out.
I did a quick wear test, screwing the screw in and out many times while pushing hard against the drill. Then I had the idea of setting it up to use the screw to lift my table saw. Again, up and down many times, no sign of wear.
I am using a piece of oak here. Soft woods like pine or spruce would not hold up as well.
Dad's wooden door
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