Cutting Wooden Threads General Woodworking
I’ll admit, I have been a bit obsessed with cutting threads. I have tried two different methods to do it: one was a stand alone thread cutting machine, while the other was done on my router table to cut the spiral groove for the handle on my meat mallet. The machine did a great job, but is cumbersome to work with and is too much of a specialized build for something that will not be used often. The idea to cut threads directly on the router table with a simple jig is what I am really interested in, and that’s the focus of this article.
As shown in the meat mallet article, the system relies on a pin follower that will guide the stock past the cutter to cut the threads.
In order for the pin to work, the start of the thread needs to be cut to guide it. The first method I tried was to wrap a 1/4″ strip of paper around the dowel in a spiral and just manually line it up with a pointer as I rotated the dowel:
This is a little tricky, but seems to work well:
A little shaky, but it should work well enough.
With the lead in thread cut, it followed the pin to cut the rest of the thread:
It turned out impressively uniform, but there was a small amount of waviness.
That was the right hand thread, now to try a left hand thread. Again, I wound the paper at the start:
This time I taped on a pointer, thinking it would be a more accurate way to line it up.
I was able to cut the lead in well enough, but when it engaged in the pin to continue the cutting, there was a lot of bit chatter and the threads turned out much worse than the right hand thread (as explained a bit more fully in the video below).
Basically, a small variation in the lead in is magnified further down the thread until the threads are unusable. This was more of a problem for the left hand thread because of the bit rotation and stock rotation caused more chatter, creating more play.
To try to make the lead in more smooth, I tried a previous idea – cutting the dowel at an angle that matches the thread pitch:
It worked, but I was still getting chatter and a lot of variation in the thread.
Next, I glued a plywood disk to the end of the dowel that is tilted by half the thread pitch:
This would ride against a fixed point while turning to cut the lead in:
A lot more complex to set up, and it really didn’t do a better job than just cutting the dowel at an angle.
It’s at that point that I realized that the real problem was with the pin follower, and how it references a very small portion of the thread to guide the cutting. I figured a wider contact area would negate and small variation in the lead in and create a smoother thread.
So, I used a piece of 1/2″ dowel and shaped it to make a wide follower:
I had to remake the holder for it so that the angle could be adjusted to match the threads being cut.
With the new follower set up, I recut the lead in using the paper strip method:
And ran the dowel through for a test cut.
The results were much better. Despite some variation in the lead in, the threads turned out smooth and uniform. They actually get better the further down they go:
I made a short video of the action:
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At some time in the future, I will make a final version of this jig that will handle a variety of dowel sizes and threads. I also have a few ideas on making wooden nuts for them easily.