a standard wrench, or the rear
guide can be held in the chuck of
a drill press, lathe, or mill to tap
holes as they are drilled. The tap
is always in perfect alignment and
the solid rear support reduces
stress on the tap.
specialized jobs in hard to tap
materials and they all have the
major drawback of trapping chips
in the tap’s flutes. This negates the
chip clearing abilities of spiral flutes
and you will need to clear out the
kerosene and a little machine oil.
Most plastics can be tapped dry or
with liquid soap — remember to
wash and oil the tap afterwards to
stop it from rusting.
What Can Go Wrong?
Tap guides are your secret
weapon to perfect results.
There are many commercial
options or you can make
your own for free. I use nylon
or UMHW plastic off-cuts to
make custom guides; they are
very quick to produce and
wear quite well. The green
nylon one in Photo 3 handles
all the metric and imperial size
taps I commonly use up to
3/8”, with room for more.
There are many commercial
guides available; one of
the better ones is the steel
guide at the bottom of the
photo. It is available from
(part# 3427 or 3428).
Photo 3. Selection of pro and home-made guides.
If the tap rotates jerkily, if
it makes clicking or grinding
sounds, and if it takes more
force than expected to turn
the tap, then you probably
have lubrication problems.
This requires an immediate
change in lubricant or using
more of it. Some of these
symptoms can also be caused
by using the wrong surface
coating on the tap or a blunt
tap; check this out if the
symptoms persist after
Now that you know
what tools and lubricants
to use, it’s time to make
some perfect threads.
Starting the Cut
You need to use a
lubricant for most tapping
jobs. The lubricant extends
tool life, creates better
formed threads, and reduces
breakage – all things that you
want. There is a lot of hype from
manufacturers about their
magical products and the dire
consequences of not using them.
For the most part, you can safely
ignore the hype and save money
as detailed below. Whatever lube
you try, apply plenty of it and
reapply whenever you clear chips
from the tap.
First, apply the correct
lubricant to the tap. Next,
you need to line the tap
up vertically over the hole;
this is where those guides come in
handy. Using just a little downwards pressure, start screwing the
tap into the hole. After the tapered
part of the tap is well into the
hole, start to reverse the tap about
half a turn occasionally. I have read
many opinions on how often to do
this; about every second or third
turn seems right. Reversing the tap
breaks the chips up and reduces
the chance of jamming.
Photo 4. Tap guide in action.
For most situations, I get excellent results with a light oil; usually
the first bottle of engine oil that
comes to hand. Spray lubricants
like Tap Magic or even WD40 can
work well. The spray helps flush
chips out of the tap flutes. Heavier,
sulfur-based oils like Mobilecut are
reserved for harder steels, while
aluminum cuts better with light oil
thinned with about 10% kerosene.
There are many heavy greases
and solid stick lubricants sold for
tapping. They are usually meant for
Brass and bronze cut best with
Unless you are using a
roll-forming tap, the cutting action
produces curly chips that quickly
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