OldTools Archive

Recent Bios FAQ

274579 Thomas Conroy 2021‑09‑19 Re: Wood tap and die
James Warburton wrote: "In my experience trying a second pass is a recipe for
disaster. If the wood is soaked in oil it cuts like butter the first time;"
and James DuPrie wrote: "I've always cut in one pass (I have a set of cheapo tap
and dies I got about 30 years ago to experiment with. My biggest is 1"). Use a
good straight, tight grained wood. I always cut them dry, and use the "1 turn
in, 1/2 turn out" rule. Never had any real problems if I made my own dowels.
Store bought dowels never worked for crap though."


Pretty much my own experience.

I learned to thread steel in junior high by the one advance - one-half back
method, so I used that at first; but eventually I decided that the half back was
breaking off good thread as well as clearing the chip, and I stopped doing it.
As much as possible I turn the entire thread in one steady pass, because for me
if I pause to shift my hands I tend to get a little jog in the cut surface.
Trying to make a second pass along the whole screw is always disastrous for me.
I always lubricated/soaked with BLO because I was going to use that for the
finish, and I didn't mind having surfaces contaminated with it. I went through
various soaking times, from just a wipe on to six or eight hours, but ended up
soaking a few minutes just before I cut the thread; you can see after cutting
how little the oil actually penetrates the wood, and it doesn't seem to go
deeper in hours of immersion than in minutes. After the screw was entirely done
I would immerse the screw completely in BLO for hours, long past the point when
bubbles kept coming out, then drain it and warp it in paper towels to blot it,
with a wrap of twine along the thread to push the paper towels down into
contact, leave it like that for an hour or two to blot off anything from the
surface. When the thread came out of the oil it was very delicate, and before I
learned to be careful I once or twice broke off bits of thread with a brush of
the hand, but after a day or two it firmed up and I think that the BLO made the
thread stronger once it had cured.

I cut my blanks on a slow foot-treadle lathe, running maybe 400-600 r.p.m.m and
I found that it was best always to cut the handle base/bearing surface from the
same piece of wood as the screw. If I made a thread on one dowel and then glued
it into the handle, the force of tightening the final press would often pull the
thread right out of the handle. After completing the thread and before soaking
it in oil I would put the screw back on the lathe and smooth down the working
surfaces of the thread using a triangularl file or what I think of as a "thread
float," a tool I made, sort of a mixture of a gunstock-checkering tool and a
cabinetmaker's float, which I could make coarser than a file but finer than an
actual float would be. Repeated passes both smoothed the thread and opened it
out a bit so that there was more play in the completed press/vise; play is
needed to avoid jamming or freezing over time.

All this is for the male thread; the female thread is completely different, and
much less apt to go wrong. I wipe BLO down into the hole to lubricate. After the
first pass with the tap I make repeated passes to open it out morel "wallering
it out" by angling the pressure toward the compass points as I make the repeated
passes. The completed female thread always is pretty rough looking, but
roughness doesn't seem to harm its durabilty or make it run less smoothly.
Have to go get my walk, almost too late for it.
Cheers!
Tom

Recent Bios FAQ