I'm slowly working on Pat Warner's Router Table Fence, aka "Precision
Fence" (see Fine Woodworking #144 (Oct. 2000) - "Micro Adjustable Router
Fence" and http://www.patwarner.com/routerfence.html [soon to be
revised]) and have some questions about taps and tapping in wood. Pat
specifies tapping for some of the assemblies and refers to his article
in Fine Woodworking #126 (Oct. 1997) "Threading Wood for Machine
Screws", p. 63, where he features four sizes for thread holes: 9/64",
13/64", 1/4", 5/16".
I recall from metal working days that taps come in sequence, e.g.
"taper", "plug", and "bottom". For an informative and concise summary
of tap and tapping, I found the following site helpful:
My questions are, all in connection with tapping wood:
1) Do you use a sequence of taps, e.g. a taper and plug, of just use a
plug? I was reading at the web site referenced above about the
compression of the threads and wonder if using a sequence of taps
produces a better thread because each tap helps compress the threads.
(The tap photographed in Pat's article looks like a taper tap.)
2) Do you use the recommended drill size for the tap, or try something
more or less since we're tapping into wood?
3) Should one strive for American National and Unified Screw Thread
system's "Coarse UNC" or "Fine UNF"?
4) What about using linseed oil both as a lubricant and something to
help harden the threads -- you'd let the holes dry for a day or two
before inserting the screws?
Are entertaining these question making my progress slow?? Answer: yes.
I use metal taps for tapping hard wood. Usually I use taper taps because (a)
I have a set and (b) I have through holes for jigs and such. Plug taps will
work well but I think you get a better and straighter start with a taper
tap. Remember that wood moves and it is sometimes a good idea to let the
wood rest and retap a day later. My lack of patience generally precludes
that. I even make face paltes and glue blocks for my lathes by tapping hard
wood blocks. Maple easily holds well enough for me to chance a 14" bowl for
finish turning at 600 rpm.
God bless and safe turning
Truro, NS, Canada
No reason to do so...just use a taper for easy entry.
That would depend on the hardness of the wood.
I'd use coarse, doubt fine would work well in wood.
You don't need a lubricant and linseed - or any other oil - won't make
the threads any harder (the wood is harder than dried oil). What
*will* firm up the threads is cyanoacrylate glue (Super glue)...do
your threads, run in super glue to saturate threads, let dry, retap.
On Tue, 12 Sep 2006 11:22:49 +0000 (UTC), Bruce Barnett
I ordered their spindle tap several months ago and it's still on back order...
and we're moving out of the country in a month.. *sigh*
Plug and bottomming taps are normally applicable only to the tapping of
blind holes when it is neccessary, for some reason, to extend the depth of
threads to nearly the full depth of the hole. An example would be sight
mounting screws on rifle barrels. Where blind holes are not essential for
some reason (same example) they are generally to be avoided. Use thru holes
instead and stick to taper taps. You might also consider the various type
of threaded metal inserts designed to be used in wood, especially if the
screw is to be loosened and retightened more than a few times.
I second this advice. They make some real nice threaded inserts for wood.
Since you are making a machine tool part, the ability of the screws to cinch
down tightly makes this desirable.
Why scrap a part because the quaint wooden threads fail while you are
I'd stick with coarse or taps and dies made for wood.
The instructions that came with the wood taps I have say to use
a lubricant like linseed oil.
Every antique wooden hand screw clamp I have ever seen in the
"as found" condition was coal black, indicating to me that the
old-timers used linseed oil on them. If you clean the black off,
there is wonderfully patinated wood, typically yellow birch,
underneath the gunk.
I would not use a drying oil like _boiled_ linseed oil for fear that
it would glue the male and female threads together. Even if
it was thoroughly cured, there is a lot of heat generated
by friction between the threads so it would not surprise me
to see some of the cured oil soften and then reset, like the
hot-melt glue used on nails.
I lubricate wood threads with a mixture of light and heavy mineral
oil (baby oil and laxative) with parraffin dissolved in mineral
Since I haven't tried anything else, I can't say how it compares to
Changes in humidity still cause the threads to bind from time
to time. A wooden dowel (or hole) that is circular at one
ambient humidity is not circular at any other.
plug is the same as bottom (at least in the UK) The sequence of three
is "taper, second, plug"
Second should be used for starting small holes in soft materials, such
as small holes in aluminium sheet or wood of almost any size. Taper
works fine if you do it right, but the small amount cut with each turn
makes it all too easy to strip the thread out while you're cutting it.
A coarse thread is essential, and some thread forms are mrginally
better than others. Whitworth (UK) or UNC (US) are good choices in hard
maple and the like. BSF, UNF and the typical metric threads are no use.
Dedicated wood threads are even better and important if you're using
softer timbers, such as beech. OTOH, Whitworth / UNC have much easier
availability, particularly if you're trying to make one component in
Other thread forms like Acme or buttress work great (especially for
clamps), but they're hard to cut with a tap or die, because of their
sharp corners. You might do well with a pair of taps (the first
taper/second tap also has the corners radiused) and cutting the male
thread with a single point tool instead of a die-set.
Some hard timbers, like hickory, are poor for thread cutting. They're
strong in bulk but they're too "stringy" to give a good thread form.
Others, like softer but fine-grained tropicals, are surprisingly good -
as any turner can tell you. It's worth reading Holtzapffel for advice
Large threads in hard maple can usefully be lubricated on cutting, just
to keep temperatures down and stop the tap sticking (beeswax). It
doesn't seem to help cutting much, but it certainly reduces the turning
Cyano afterwards is worth it too, particularly if you have vacuum
available (run the tap through again afterwards). Any thread in wood is
a bit of a "dog on its hind legs" situation and any help is worth
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.