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274574 Thomas Conroy 2021‑09‑17 Re: Wood tap and die
O Galoots: 

I'm under the weather today and not up to proper snipping, and over the years
I've posted so many thousands of words on this topic that I am tired, tired. But
a few points arise.

For the male screws, the threadbox is very pick about wood, and it goes way
beyond just using even-grained species. Well-aged beech is one of the best
woods, but fresh beech will shrink so much that after a couple of years the
screws may pull right out of the holes. Happened to a friend of mine. Cherry is
too brittle; the thread will break off as you cut it. I destroyed about four
yards of 1" cherry dowel learning that. The very best screws I've made were from
split black locust, if you can get it. Black walnut is in my experience the best
commercial wood, provided you pick it carefully enough that the grain is as
straight along your screw as a split blank would give. Maple will do, but it
tends to give a slightly rough screw. Don't worry about the crap Beall tries to
feed you about the importance of a precision-cut wood blank; oh, it's important
for their router jig, all right, which registers on the outer surface of the
dowel, but a screw box registers on the screw itself, on the surface you have
just cut, so all that really matters is that it isn't too big. Don't forget that
wood is constantly shrinking and expanding; the precisely circular-section blank
that they ship you from Ohio will be an oval the day after you take it out of
the box in California. On the other hand, having straight grain dead along the
blank is really important; if you can turn your blanks, its better to use split
wood; if you must use dowels, or commercial saw-cut turning squares, I'd reject
nineteen out of twenty based on grain running out. Old ikea chair legs are a
good source for well-aged beech, if you can turn them down. Just about any
reasonable hard wood will do for the female threads, even modern mahogany so
soft you can dent it with a fingernail. Modern mahogany is unthreadable, it just
gets chewed up by the screwbox because it is so soft, but even mahogany will
take female thread and make good press (vise) cheeks.

The Chinese and Taiwanese screwboxes with aluminum lead sections are "Conover-
style," pirated from a very well-designed and well-made line that Ernie Conover
sold decades ago. It was conover who revived the screw box-tap after it had gone
out of production in England and Ameriica. Conover had a proper balance of pitch
(threads per inch) and diameter, with 7 t.p.i. on the 3/4" size (if I recall
correctly) and 6 t.p.i. on the 1". Traditionally, a 1-1/8" size would have had 5
t.p.i., 1-1/4" would be 4 t.p.i., and above that you would have to go to two-
cutter screwboxes. A screw for a bench vise might be 2-1/2" diameter and two or
three t.p.i. Conover only made threading kits up to 1" but after the Chinese
ripped him off they soon found that there was a demand for bigger screws; so
they introduced a 1-1/4" size and a 1-1//2" size, and maybe some larger ones.
The trouble was, since they were copying without knowledge or understanding,
they gave all the sizes above 1" the same pitch and cutter size: 6 t.p.i. This
is pitch is workable but a bit small and slow for a two-screw wooden
bookbinder's finishing press, functionally identical to the so-called "moxon
vise"----I know what I'm speaking about here, I've made dozens of them with my
Taiwanese screwboxes. I-1/4" and 6 t.p.i. is very slow unless you "twirl" the
press like a hand clamp to open and close it, but still functional. 1-1/2" at 6
t.p.i. is bad in every way. Check the archive for explorations of the problems.


If you want to make the kind of half-assed flat-cheeked dovetailing jig that
Chris Schwarz invented and dubbed "Moxon vise," then a 1" or 1-1/4" Taiwanese
screwbox will do just fine, at least up to 15" between screws--- my experience
doesn't go much larger than that, but I would want a larger, faster screw for a
length greater that that. If you want an installed bench vise that is more than
a toy, you will have to go to a German two-cutter screwbox in a size of or over
1-3/4" and 3 t.p.i., and a cost of upwards of $500.00 or $1,000.00. For smaller
screws, up to 1-1/4 with 6 t.p.i., the Taiwanese/Chinese sets still seem to be
good tools at a great price. This was certainly true when I bought mine, but
that was thirty years ago. Router jigs are an option, if you make your own, and
the very best of all is a screwcutting lathe if you have the capacity for a
large pitch (2 t.p.i. to 5 t.p.i.) and if you can make or find the special shape
cutters that are needed for large wood threads. Or if you have the money, the
German screwboxes and taps (used to be available from Dieter Schmid, I think)
are the gold standard, with no downside except their price.

I've run out of steam, and I'm starting to repeat myself, which is bad even if
you catch it and erase it. But this is not a new topic; browse the archives.
Tom ConroyBerkeley

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