with use of LEFT-HAND Drills
by
Mark Hamilton
Removing
broken bolts is one of those pesky jobs that few people
look forward to.
This is one of those “try-it-you’ll-like-it”
methods. During many years of working with cars and machinery this
method has proven to be very successful.
The
champion of methods
for
removal of stubborn broken bolts is to drill them
out, using a left hand drill bit and a
reversible drill.
(The good quality, variable speed, 3/8"
models, which produce good torque at low RPM, work best.)
As always with drilling holes, drill a small
“pilot hole” first, then drill a larger hole through
the broken fastener.
(It’s easier to drill centered and straight by
using a small drill first, but be careful not to break the
small drill!) Most
bolts come out before the hole drilling operation is
finished. (Then there is no need for "easy-outs,” which
sometimes break off in the drilled hole and make matters
worse.)
We
just happened to have a few tightly rusted studs and nuts,
which all broke off when attempting to remove the nuts.
The project was rear fender mounting studs in a
1930 Model A FORD. These
studs are threaded into fixtures at the body, behind the
rear wheel, where seventy years of road grime splashed on
them. And
back in those years nuts and bolts were not plated with
zinc or other anti-rust coatings, as our modern fasteners
often are. The
nuts were nearly welded to the studs by rust, and the
studs were equally rusted into threads at the body.
It was impossible to remove the fenders without
breaking the studs. This was about the worst possible case of corroded and rusty
fasteners.
In
photos, we will show the removal of the old studs, and
also the tools we used for this work.
The
first step is to flatten the surface at the end of the
broken bolt. Where
bolts have broken, the surface is often jagged and sloped,
which will cause the drill bit to wander off-center, when
attempting to drill the hole. The stud in the photo was broken just above the surface, and
we used a grinder to flatten the surface at the broken
stud. When a
bolt is broken off below the surface of a threaded hole, a
jagged break often can be flattened with punches to get a
better surface for drilling.
We used a heavy
hammer and center punch to leave a “dent” for the
drill to follow. Without
center punching first, it would be impossible to keep the
drill in the center of the bolt.
Before this step, we drilled a small pilot hole using a 1/8th
inch drill. (The
small diameter drill is easier to keep straight and
centered than a large diameter drill.)
Then we used a ¼ inch drill to finish with this
5/16inch stud.
The drill will
attempt to grab the bolt just when breaking through the
backside. Typically,
that’s the moment when the broken fastener will spin out
of the threaded hole.
Also, when drilling through the broken bolt,
vibration will help to break it free.
And drilling completely through leaves the bolt as
a hollow tube, which may allow it to slightly collapse and
loose some its grip at the threads.
This classic
case of rust frozen fastener, shown above, came out
squealing and with much powdered rust pouring from the
threads. Notice
that the threads at the fastener are even galled.
Before installing a new stud we oiled the threaded
hole and cleaned the threads with a tap.
Notice
that these are LEFT-HAND drills,
and they must be used with a reversible drill.
Ours are by Snap-On tools, and Snap-On offers more
than one model of Left Hand drills.
Snap-On tools are typically excellent in quality,
but other tool companies also make left-hand drills.
(Check with the tool dept. at Sears, or your
favorite tool store.)
The
drills in the set shown above are short length
High Speed Drills, and are rated for drilling in steel and
other metals.
The set shown
below are COBALT, long length, left-hand
drills. The
Cobalt is harder material than the standard high-speed
drills, and the Cobalt drills are our choice for drilling
out grade 8 bolts.
The short-length drills, used with an angle-head drill motor, can get
into places where lack of clearance would prevent working
with a long drill and typical drill motor.
Sometimes
the longer drill bit with typical drill motor is needed to
reach down into places where the angle-head and short
drills would not work.
What ever the
set-up used, the DRILL MOTOR should be powerful enough to
drill at low RPM without stalling. Smooth running, powerful, and strong even at low RPM drill
motors are best suited for this work.
IMPORTANT
As
with any drilling operation, watch for chips while
drilling. When
making chips material is obviously being removed.
If the drill is smoking and not making chips, then
stop immediately. The
drill may have to be sharpened, and probably reduce the
RPM while drilling.
If a
fastener does not come out with this left hand drill
method,
there are various types of “easy-out” extractors.
Or, sometimes there is opportunity to drill an over
size hole and then re-thread the hole to the next size
larger.
Some applications can use the next size larger
bolt, otherwise the “heli-coil” method can restore the
threaded hole to its original size.
But, these alternative methods will require
drilling first, so the left-hand drill method is never a
wasted effort.
Two types of “EASY-OUT” extractors are shown in
the photo above.
When available, the type on the right is a favorite
and has been less likely to break off in the broken bolt.
But the three at the left have also been
successfully used to remove broken bolts.
Especially in soft aluminum, the “HeliCoil” thread repair kit is
very useful. The
hardened steel thread insert actually adds strength when
used in soft metals such as aluminum.
The method is to drill the proper size hole for the
next size larger thread tap. Then cut new threads in the drilled hole using the tap.
And then use the tool to install the new thread
insert. The
thread insert is threaded both inside and out.
And
always when using a thread tap,
turn it in about 1/3 turn at a time, or until it begins to
feel snug. Then
back it up to cut the removed material.
And then turn the tap in some more.
(Simply forcing the tap into the hole will plug the
tap and not result with good threads.)
TIP
A stud
is stronger than a bolt,
especially
when the threads are questionable, which sometimes is the
case after struggling to remove a broken bolt from a
threaded hole. Minor
damage to threads when struggling to remove the broken
bolt can reduce the strength of the threads.
And then when the new bolt is tightened into place,
sometimes the remaining threads will pull out.
With correct
stud installation, the stud is screwed into the threaded
hole without applying pressure to the threads, and without
galling the threads.
After stud installation, the part is slipped over
the stud, then install the correct washer, and then
tighten the nut.
The stud is
stronger because thread contact at the stud and at the
threaded hole will be stationary at the time pressure is
applied (when tightening the fastener).
But when a bolt is used to mount a part, the bolt
is rotated in the threaded hole during tightening, which
can tear out weak threads.
When
installing the stud into the threaded hole, the author
prefers to strengthen and anchor the stud into place with
Loctite. (Rather
than double nut the stud and force it against the bottom
of the drilled and threaded hole.)
The “red version of Loctite,” is preferred.
(“stud and bearing mount” purpose version,
it’s the permanent version)
No
doubt there will be times when clearance problems will
make it impossible to use a stud, rather than a bolt.
Sometimes there is not room to slip a large part
over a stud, but rather the part has to be slipped into
place from the side. (The stud gets in the way–making it impossible to slip the
part into place from the side.)
But when a stud can be used rather than a bolt, the
stud will result with greater fastener strength than the
bolt.
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