From time to time, the question of how to cut big coarse threads in wood comes up in discussion. People want to make "Moxon" vices, or special clamps, or an all-wooden bench vice, or an end vice. Over a decade ago, I did some experiments and wrote them up on a forum, but my pictures aren't there any more, so I thought I would revive the topic on here. I'm pretty sure the subject came up within the last few months, but can't find where at present. Anyway, this is what I did back then.
I'd already played about cutting wooden threads with the sort of generic Taiwan-made thread cutting tool that Axminster still sell here. (Those tools are ok, but not generally available in the larger sizes that people need for bench vice screws and the like. And big antique ones tend to cost quite a lot, especially the rather nice metal sort made by Peugeot and others. )
First off, I turned a tidy cylinder of nice, fine grained hardwood on my woodturning lathe. I was lucky enough to have got some holly when the neighbours cut a tree down, which is as good as boxwood for this sort of thing. My trial piece was about 1¾" in diameter. I transferred it to my old treadle driven Barnes metalworking lathe, which copes with thread cutting down to 5 threads per inch. I held the wood in a three jaw chuck at one end and a revolving centre at the other. The screw was a stop against a marked jaw, to make sure that everything stayed in the same positions when taking successive threading cuts. The photo below shows how I set up a conventional single point tool, such as you'd use on steel. squared against the stock.
With back gears on and the right combination of change gears in place, I tried cutting a thread with that metalworking tool.
Hopeless!
Cutting this with the metal tool was not a good idea. Even on nice hard dry wood like the holly, and taking a very shallow cut, the result was a fuzzy mess of broken fibres. I took my blank back to the wood lathe and turned away the mess, leaving it at about 1½" diameter, to try again.
Luckily I had a better idea. The tool holder I was using takes 3/16" square HSS blanks. By one of those rare bits of good luck the cutting tool inside my cheap ¾" thread cutter is on a 3/16" square body. It was pretty simple to remove it, clamp it in the tool holder and shim it up with some bits of steel so it hits the work at something like the right angle. Success!
A nice clean cut, which I could deepen with successive cuts until the threads were fully formed. (Here I had set the cross slide at 30 degrees, which meant I could advance the cutter on one side of the thread only. This is easier than cutting the full depth on both sides at once and is a normal technique. You can see that the shaving is only coming off the left hand side.
To make a matching female thread, I used an expansive bit to bore a suitably sized hole in a bit of beech:
Experiments and discussion at the time led me to harden the inside of the hole with some poundshop CA glue
Here's the single point cutter that I used:
and here it is disappearing into the beech making an acceptable cut on the CA-reinforced side grain (apologies for poorly focused picture).
By this time I had managed to find some old coarse thread chasing tools in my chosen 6 tpi; with a fresh dose of CA on the initial surface, I was able to use one of these to slightly enlarge the internal thread, so that I got an easy, running fit, rather than one which needed two hands to turn it.
And here's my finished experimental piece, which I was quite pleased with at the time.
Now, I know that not everyone has a century old treadle lathe to play with, but I want to stress that what I did here doesn't need one. I wasn't using the treadle; i just pulled the work round by hand - the cut doesn't need to be made quickly. So I would think that anyone with a lathe with a leadscrew on would be able to do something similar, as long as you have the right change gears.
You don't need to buy a threading kit to get the cutter - you could also use a carver's V-tool which has exactly the same cutting action - but you would need to work out some suitable way of holding the cutter tangential to the wooden cylinder.
I'd be interested to see other people's approaches and experiments.
I'd already played about cutting wooden threads with the sort of generic Taiwan-made thread cutting tool that Axminster still sell here. (Those tools are ok, but not generally available in the larger sizes that people need for bench vice screws and the like. And big antique ones tend to cost quite a lot, especially the rather nice metal sort made by Peugeot and others. )
First off, I turned a tidy cylinder of nice, fine grained hardwood on my woodturning lathe. I was lucky enough to have got some holly when the neighbours cut a tree down, which is as good as boxwood for this sort of thing. My trial piece was about 1¾" in diameter. I transferred it to my old treadle driven Barnes metalworking lathe, which copes with thread cutting down to 5 threads per inch. I held the wood in a three jaw chuck at one end and a revolving centre at the other. The screw was a stop against a marked jaw, to make sure that everything stayed in the same positions when taking successive threading cuts. The photo below shows how I set up a conventional single point tool, such as you'd use on steel. squared against the stock.
With back gears on and the right combination of change gears in place, I tried cutting a thread with that metalworking tool.
Hopeless!
Cutting this with the metal tool was not a good idea. Even on nice hard dry wood like the holly, and taking a very shallow cut, the result was a fuzzy mess of broken fibres. I took my blank back to the wood lathe and turned away the mess, leaving it at about 1½" diameter, to try again.
Luckily I had a better idea. The tool holder I was using takes 3/16" square HSS blanks. By one of those rare bits of good luck the cutting tool inside my cheap ¾" thread cutter is on a 3/16" square body. It was pretty simple to remove it, clamp it in the tool holder and shim it up with some bits of steel so it hits the work at something like the right angle. Success!
A nice clean cut, which I could deepen with successive cuts until the threads were fully formed. (Here I had set the cross slide at 30 degrees, which meant I could advance the cutter on one side of the thread only. This is easier than cutting the full depth on both sides at once and is a normal technique. You can see that the shaving is only coming off the left hand side.
To make a matching female thread, I used an expansive bit to bore a suitably sized hole in a bit of beech:
Experiments and discussion at the time led me to harden the inside of the hole with some poundshop CA glue
Here's the single point cutter that I used:
and here it is disappearing into the beech making an acceptable cut on the CA-reinforced side grain (apologies for poorly focused picture).
By this time I had managed to find some old coarse thread chasing tools in my chosen 6 tpi; with a fresh dose of CA on the initial surface, I was able to use one of these to slightly enlarge the internal thread, so that I got an easy, running fit, rather than one which needed two hands to turn it.
And here's my finished experimental piece, which I was quite pleased with at the time.
Now, I know that not everyone has a century old treadle lathe to play with, but I want to stress that what I did here doesn't need one. I wasn't using the treadle; i just pulled the work round by hand - the cut doesn't need to be made quickly. So I would think that anyone with a lathe with a leadscrew on would be able to do something similar, as long as you have the right change gears.
You don't need to buy a threading kit to get the cutter - you could also use a carver's V-tool which has exactly the same cutting action - but you would need to work out some suitable way of holding the cutter tangential to the wooden cylinder.
I'd be interested to see other people's approaches and experiments.
