Saturday, May 25, 2019

Ash log Roubo project 4, leg vise spindles and chops.

During my final trip on the Troms Capella, I used the ships lathe to turn a tap for making wooden threads.
It makes a 2" thread with a pitch of 4.5 modules. Modules is actually just a fancy word for Pi mm, so the thread is 14 mm or pretty close to 9/16"

It seems as though I only took one picture while making the tap, and now it is at home, so I can't really take anymore pictures of it at the moment.

The tap worked really well, despite ash not being the easiest wood to turn a thread in.
After making the internal threads in the legs, I watched an episode of Roy Underhill, where he makes a die for wooden threads.
I basically copied all he did, and though I couldn't do it as fast as him, eventually I ended up with a die that could produce a thread.
The first spindle looked utterly magnificent, with the slight but important part - it didn't fit..
I had to do quite a bit of adjusting to get the die working in a way that produced a spindle that would work. But finally I had two spindles (made out of whitebeam).

I turned a couple of ends for the spindles out of some apple, and glued them on. Then a hole was drilled through, and a couple of sticks were turned and inserted.
Those sticks were retained using small ebony pegs, so technically I can't keep on claiming that the entire bench is made from the same tree.

The chops were made out of the ash log, and I made those a bit tapered to make them look nice.
A square recess was chopped in each of them to receive a garter for the spindle.

Completed spindle.

Close up of cutting action of the die.

Turning a spindle blank on the metal lathe.

Fabricating a 2"/4.5 module tap.

Two pieces of ash for the vise chops.
Recess for the garter.


  1. That screw looks awesome! And whitebeam is the perfect wood for it. Did you have to wax the screw, or does it move smoothly on it's own?

    1. Hi Brian

      I waxed the screw with an old candle to get it to run smoothly. But I think that the main issue is that the threaded hole is the thickness of the leg i.e. 4", so it's a rather long threaded hole that will inevitably result in a bit of friction.


  2. I'd love to know the secret of making the die for wooden screw threads. I tried that a few years ago with only minor success (read: not good!) and would love to revisit that someday rather than buying a threading tap and die from Beall. How many adjustments / how much trial and error was involved for you in making the die-box? And were the adjustments mostly in locating the cutter or sharpening the cutter?


    1. Hi Matt
      I wish that I could shed a bit of light, but I haven't found the secret myself either.

      I only did adjustments of the position of the cutter, by shimming up/down with some shavings.

      I think that technically I ought to make a new cutter, because when the thread is done, the outer diameter is smaller than it should be. Ideally it should be maybe 3/32" smaller, but mine was maybe 3/16" smaller. My biggest challenge was that the pitch of the spindle would gradually change over the run of the entire length. It would gradually become larger.
      There has to be some sort of slop built in, but not quite that much.
      At a point I considered making the threads on the lathe, but I told myself that it wouldn't matter if they were a bit on the loose side.

      Admittedly it doesn't help that the thread is very coarse, and I only made a die with a single cutter.
      Dieter Schmidt carries a line of taps and dies, and when the thread diameter becomes large, they will sport two cutters.
      The only problem is that they are very costly.

      Mine was modeled after an old article in Popular Mechanics probably form the 1950'ies. They suggested that the angle of the thread should be 80 or 90 degrees. I just remembered that figure, so I re-read the theory of thread design and did the calculations for an 80 degree tap.

      If I'll make another workbench, I think that I might choose to make the spindle thread on the lathe, just to get it perfect. But that would require me to find some electronic version of an instruction book for my old metal lathe, because the table of gears needed to cut module thread isn't riveted onto the lathe itself (only the one for metric and imperial thread).


  3. Like that rough thread, often find commercial ones too fine resulting in a lot of un-necessary turning of the handle.
    If you want to make the threads on your own lathe you could just hold the tap in the chuck and try the different options until you find the perfect pitch. Sound like there would be a lot of combinations possible but in reality there is only a few with that large a pitch.

    1. Hi Ty

      I like that the thread is coarse as well, It also "looks right" I think.

      I googled a bit and managed to find an old instruction manual with a thread table for my metal lathe.
      I have the possibility to cut 102 different types of pitches, if I mount the correct gear wheels. For the Module pitch, I need to mount 4 correct gear wheels, before choosing the correct settings on the levers.
      If I miss the correct gear, the thread just isn't going to work.
      Here's a link to a picture of the thread table for the lathe.

      I just hope that I have all the correct gear wheels, but I can check that once I get home. After all the lathe is probably from the 1950'ies, so a few gear wheels might have disappeared when the lathe was moved around between different owners over the course of time.


    2. Oh did not see that your lathe was the type with exchangeable gears, that make things a bit more complex.. But still, given that you acually have the right gear, there can only be a small amount of the combinations that has that coarse a thread. Good luck!

    3. Ty, you are an eternal optimist :-)

      I guess I'll have to check when I get home, and I think that I might need to open the front of the gear box as well, as I expect there is a loose securing pin. I suspect that because if I put it into a certain gear combination, it will just give a loud clacking noise and not actually turn the feed shaft.

      But luckily those old machines are possible to repair, so it could also be the security pin that is supposed to break when people forget to loosen the automatic feed and the main apron hits the casting of the gear box.