clog up the flutes and can cause
tap breakage. In shallow through
holes, the chips can be washed out
with lubricant or blown out with
pressurized air. In deep or blind
holes, you will need to back the
tap out, brush it off, and extract
the remaining chips from the hole.
If you are tapping a through hole,
I suggest quickly brushing the chips
off the end of the tap before
winding it back out of the hole.
Once all the threads are cut in
a part, it needs a final cleaning to
remove any leftover chips and the
lubricant. I flush holes out with
kerosene or isopropyl alcohol,
followed by soap and water for
non-ferrous parts. Chips in plastic
parts often refuse to wash out;
use a small dry wall or sheet metal
screw to pick the stringy chips out.
Sooner or later, you will break
a tap in an important piece of
work. Taps break for many reasons.
Here are the top five:
Misalignment — If a tap is
not lined up with the hole, it will
break from a combination of
bending and excess torque. Using
a guide will eliminate this.
Undersized hole — Taps will
break from excess torque as they
try to cut over 100% of the thread
depth. Consult your drill chart
and pick an oversized drill when
Blunt taps — Taps will break
from excess torque when you
try to power dull cutting edges
through your workpiece. Check
your taps before use and
remember that they are a
consumable item; it’s okay to
throw them out.
Chip packing — As chips pack
up in the flutes of the tap, they
can be forced back into the cutting
area, jamming the tap suddenly;
sometimes you can’t even back the
tap out. Remember to regularly
flush out the hole or back the tap
out for cleaning.
Sideways stress — If you
bend the tap off-axis, it will very
likely break. A tap guide can help,
but learning to apply even pressure
to both ends of the tap wrench
What to Do When a
Removing a broken tap can
be difficult to nearly impossible.
Commercial extractor tools
generally work for shallow holes,
but fail miserably when a tap is
wedged into a deep hole.
When a tap breaks off, try
G rind the tap flush, then drill
and tap a new hole close by. It
sounds like a cop-out, but this is
often the simplest solution.
Take the part to a
professional machine shop and
have the tap burnt out with an
EDM machine. Keep in mind
that this is only practical for
expensive parts and the part may
G rind the end of the tap flat,
then drill it out with a carbide drill.
This is a slow but reliable option. It
requires a drill press or mill to keep
the carbide drill on target. If you
can use a lefthanded drill, the tap
will sometimes screw itself out of
You now have all the
techniques and theory to produce
great threaded parts and to
build better robots. So, go forth
and thread! SV
Completed and Upcoming Events
Completed Events May
18 - June 17, 2009
RoboGames was held June 12- 14th.
August - September
Gulf Coast Robot Sports-2 will be held in Bradenton, FL on July
House of Benson — Barnyard Brawl II will be presented by
the North East Robotics Club in
Winchendon, MA on August 15.
HORD Fall 2009 will be
presented by the
Ohio Robot Club
in Strongsville, OH
on September 12th.
24 SERVO 08.2009