|
United States
Department of
Agriculture
Forest Service
Technology &
Development
Program
2300 Recreation
August 1984
8423-2602-MTDC
 |
Dale Mrkich
Forestry Technician
Jerry Oltman
Project Leader
Photo courtesy of the
University of Montana Mansfield Library
Archives. |
|
The Forest Service, United States
Department of Agriculture, has developed this
information for the guidance of its employees, its
contractors, and its cooperating Federal and State
agencies, and is not responsible for the interpretation
or use of this information by anyone except its own
employees. The use of trade, firm, or corporation names
in this publication is for the information and
convenience of the reader, and does not constitute an
endorsement by the Department of any product or service
to the exclusion of others that may be suitable.
The United States Department of
Agriculture (USDA), prohibits discrimination in all its
programs and activities on the basis of race, color,
national origin, gender, religion, age, disability,
political beliefs, sexual orientation, and marital or
family status. (Not all prohibited bases apply to all
programs.) Persons with disabilities who require
alternative means for communication of program
information (Braille, large print, audiotape, and so
forth) should phone USDA's TARGET Center at (202)
720-2600 (voice and TDD). To file a complaint of
discrimination, write: USDA, Director, Office of Civil
Rights, Room 326-W, Whitten Building, 14th and
Independence Avenue SW, Washington, DC 20250-9410, or
call (202) 720-5964 (voice or TDD). USDA is an equal
opportunity provider and employer.
Hand Drilling and Breaking Rock for Wilderness Trail
Maintenance
Introduction
|
Courtesy of the University of Montana
Mansfield Library Archives. |
Percussive or hammer drilling is most often used to drill
rock. In Forest Service trail work, gasoline-powered hammer
drilling is common. Hand drilling is sometimes necessary
however, because machines cannot be used. This manual
describes elementary tools and techniques for hand drilling
rock.
Although hand drilling is slow work, it is a safe and
simple way to prepare rocks for breaking with explosives,
wedge and feather sets or expansion chemicals, or to accept
anchor bolts. The driller drives the steel by methodical
hammering and turning. When the hammer strikes the head of
the steel, the bit is forced against the rock. After each
blow of the hammer, the driller turns the steel slightly and
strikes it again. With each blow the bit chips small amounts
of rock that collect in the hole as "drilling dust." The
driller removes the dust by adding water to the hole, which
creates a mud that sticks to the sides of the steel. To
clear the mud, the driller removes the steel and raps it
against the rock. The procedure is continued until the hole
is deep enough; longer steel is substituted as the hole
lengthens.
The steel is manipulated with one hand while the other
hand hammers (single jacking), or the steel is manipulated
by two hands while another person hammers (double jacking).
This manual describes correct techniques, discusses proper
tool maintenance, and includes sources of tools and a
bibliography.
Although hand drilling is not commonly used in the Forest
Service, it can effectively remove rock from trails and does
observe the Chief's directive to resurrect, develop, and
utilize primitive skills in wilderness management. Hand
drilling skills have been all but forgotten; we hope to
preserve them with this manual.
No cost comparisons have been made between hand drilling
and gasoline-powered drilling. Initial tool costs are much
less for hand drilling, however, and the techniques can be
learned by unskilled or low salary employees. Since
gasoline-powered drills are prohibited in wilderness, hand
drilling allows wilderness managers to maintain trails
without violating wilderness guidelines.
Hand drilling is an effective method for maintaining forest
trails.
Description of Tools
Hand Drilling Steel
Nomenclature
| Rod |
The rod is high carbon octagonal steel bar, 3/4
to 7/8 inches wide. Length may vary from 10 inches
to several feet. |
Star pattern bit |
| Bit |
The bit is the sharpened end of the rod. |
| Bit Gage |
The cutting edge is flared on 7/8 inch steel to
a length of 1'/4 inches.* Other thicknesses of rod
have similarly proportioned cutting edges. |
| Effective length |
The effective length is the length of the steel
that is available for drilling, the total length
less the shank or hand hold area. |
| Shank |
The shank is the area near the head where the
driller or holder grips the steel. |
| Head |
The head is the end of the rod opposite the
cutting edge, and receives the blow of the hammer. |
Straight pattern bit |
| Plastic caps |
These are convenient for protecting sharpened
cutting edges during transportation and storage. The
top cap also keeps ragged edges from snagging other
items. |
| Cutting edge
angle |
This angle must be precisely maintained during
sharpening and reconditioning so the cutting edge
remains in the center of the rod. |
| Bits |
|
| Star Pattern
Bit |
Two perpendicular cutting edges, flared and
raised slightly, intersect at the center of the bit.
These are common on modern drilling steel. |
| Straight Pattern Bit |
These have a single flared, slightly raised,
cutting edge. They are old style bits, and may be
found in second hand or antique stores. |
*We have not arbitrarily chosen this size rod. Water gels
approved for Forest Service blasting are packaged in
polyester cartridges. The length of these varies, but the
smallest available diameter package is 1 inch. A 1 1/4 inch
hole is the minimum size that could easily accept that
package.
Hand Drilling Hammers
Nomenclature
| Head |
The double face hammer head is made of
heat-treated, high carbon steel. |
Single jack |
| Striking faces |
The two striking faces should have beveled edges
and should be heat treated. |
| Handle |
Wood handles are usually made of hickory. They
should have a tight, knot-free grain that runs
parallel to the wedge slot. Other handles are made
of fiberglass, or are a forged extension of the
head. |
Engineer's hammer |
| Single jack |
These are also called 'club' or hand drilling
hammers. Handles are commonly 10 inches long, and
heads weigh either 3 or 4 pounds. The short handle
is uniquely suited to hand drilling because it
resists breaking better than longer ones, and it
facilitates accuracy by requiring the hand to be
close to the head. |
| Engineer's
hammer |
These are also called long handle single jacks.
They come with a 14-inch handle attached to a 3- or
4-pound head, and work well for the drilling
technique we call modified double jacking. |
Double jack
|
| Double jack |
These large driving sledges have 36-inch handles
and 6- or 8-pound heads. Because their use requires
considerable expertise from both the driller and
holder, we recommend that you use single jacking or
modified double jacking until safety and proficiency
with the double jack can be assured. |
Wedge and Feathers
Nomenclature
| Wedge |
This is a heat-treated steel rod that is
generally the same diameter as the drilling steel. |
Wedge and feathers
|
| Blade |
Wedges have a pointed, flattened blade opposite
a head that receives the blow of the hammer. |
| Feathers |
These are half round pieces of forged steel with
a curved top, blunt bottom, and a flat inside edge
running their entire length. |
The Problem
A proposed trail may cross a rock face or, after
prolonged trail use, hazardous points of solid rock often
protrude into the tread. A trail is built in rock by cutting
some rock away to form a ledge or by removing the rock
entirely. Sometimes rocks may be chipped flat with a pick.
Hand drilling helps remove rock three ways: (1) A rock
may be split into chunks of manageable size by steel drilled
into a natural seam; (2) If the steel in the seam does not
split the rock by itself, the hole may be fitted with the
wedge and feathers. The wedge is driven between the feathers
with a hammer until the rock breaks; (3) Finally a hole may
be used to prepare a rock for blasting. In general, the
larger the rocks, the more likely you will use explosives to
move them.
Although most large rocks are moved with explosives, we
will not discuss the safe and effective use of explosives in
this manual. For this information we recommend the Forest
Service Blasters Handbook.¹ Explosives are most
efficient, however, when used in drilled holes.
There are several considerations that make hand drilling
a preferable alternative to other drilling. Gasoline-powered
rock drills are expensive, and trail operations often do not
have enough drilling work to justify costly equipment.
Moreover these machines are noisy, heavy to backpack into
remote areas, and tedious to use when they are there.
Ferrying in gasoline-powered drills and supplies must
usually be coordinated with a packer. And since motorized
equipment is prohibited in wilderness, permission to use
power drills must be secured in advance.
In short, many small drilling jobs are delayed because of
economic, logistical, or policy considerations. Personnel
trained to use hand drilling equipment could accomplish
these small drilling jobs economcially without violating the
spirit of the 1964 Wilderness Act.
History
The building blocks for the Egyptian pyramids and
obelisks were obtained by using hammers and wooden wedges to
extract large sections of stone in carefully measured shapes
and sizes. The wedges had a hole in the middle for holding
and carrying.
Miners from the time of the Roman Empire though the
Middle Ages often applied a "fire setting" system to break
rock. A rock face was exposed to intense heat followed by a
quick dousing with water. The sudden cooling caused the rock
to crack and split along natural seams. Sometimes a
suspended wooden ram with a hard stone ball on its front was
used to open a hole in the center of a rock face, and the
face was chipped into it radially.
Gun powder was first used to break rock during the Middle
Ages. In 1683 a Saxon named Hemming Hutman used a drill
forged of wrought iron with an inset bit of tempered steel
to hammer holes in the rock at critical points. The charges
placed in the holes broke the rock more effectively than
those laid on or near it.
The early history of our country contains many accounts
of legendary 'hammer and steel' drillers who were experts at
both single and double jacking. Single jacking involved an
individual holding and turning the steel with one hand while
hitting the steel with a small hammer held in the other
hand.
Single jack drilling, circa 1850. (Photo reprinted
courtesy of Compressed Air Magazine.)
Ambidexterity was very helpful for the single jack
driller because he could work longer by shifting the hammer
from one hand to the other to distribute the work. In double
jacking one or two drillers hit a drilling steel with large
sledge hammers while a holder turned the steel slightly
after each blow. As the hole deepened, the holder
substituted longer steels in a way that did not interrupt
the driller's disciplined rhythm.
 |
 |
 |
| 'Down hole' double
jacking, early 1800's. |
'Up hole' double
jacking, early 1800's. |
A prospector single
jacking, circa 1910. |
| |
(Photos reprinted courtesy of Compressed Air
Magazine.) |
Since every mechanical advantage gained by drillers was
considered desirable, hand drilling was generally abandoned
as soon as pneumatic drills were developed. Still some hand
drilling methods were retained by prospectors for small
budget rock work. Drilling and breaking rock with hand tools
is discussed in Forest Service manuals up to 1923, and in
prospecting handbooks as recently as 1943.
Some of the older techniques are not applicable today.
For example, we consider double jacking unsafe for
inexperienced drillers. Since most of today's hand drilling
will be done by beginners, we suggest you use either single
jacking or modified double jacking, a technique we
developed. Both of these methods are safe, effective, and
readily learned.
Technique
Every section of rock has its own character, and
experience and common sense will help determine the most
effective method of dealing with it. Take time to carefully
evaluate the rock's structure. Consider whether the rock is
solid or 'seamy', stratified horizontally or vertically, or
is igneous, sedimentary, or metamorphic before deciding
where and how to attack it. Work with, not against, the
rock.
The importance of properly planning the hole in advance,
that is, deciding where and how deep to place it, cannot be
overemphasized. Rock usually splits to the first horizontal
seam below the drill bit or tip of the wedge. Proper
placement will help assure that the rock will break at the
proper angle and in the right place while using the least
time and energy. Using the shortest steel necessary will
also save time and energy.
Courtesy of the University of Montana
Mansfield Library Archives.
Drilling
Always wear safety equipment, including safety glasses or
goggles and gloves, when drilling.
1. A special, short-handled hammer called a single jack
is used for one-handed drilling. Hammer heads weigh either 3
or 4 pounds, and handles are 10 inches long. The short
handle helps you place blows accurately.
Single jack driller at work.
A long-handled single jack, an engineer's hammer with a
14 inch handle and a 3- or 4-pound head, for example, can
be' used for two-handed drilling with another worker holding
the steel. The proximity of both hands to the steel required
by the handle assures that accuracy and safety are not
sacrificed. We call this technique modified double jacking.
2. The driller will be kneeling on one or both knees, or
sitting. If modified double jacking is used, the holder
should position himself across the steel from the driller,
and wear gloves on both hands.
Modified double jack drilling team at work.
Assume a comfortable position and change positions and
tasks regularly to help minimize stiffness in legs, arms,
and back. Knee pads could be an asset.
3. Grasp the hammer firmly and hit the steel squarely.
When collaring (starting) a hole, work deliberately and
slowly, placing each blow carefully. Although a drill hole
is usually started with a drilling steel, it can also be
started by chipping slightly with a pick. In the beginning
dust and rock chips are difficult to minimize. Be patient
when collaring; a hammering rhythm is much easier to
maintain after the hole has been started.
Establish your rhythm as soon as possible. Drilling with
a regular rhythm will be more productive than driving the
steel with powerful strokes in sporadic bursts of effort.
Hard hitting causes you to tire quickly and experience
cramping prematurely. It also causes the steel to stick in
the hole. Take frequent rests to prevent cramps, and do not
ignore signs of fatigue. Let the tools and gravity do the
work.
Any rest that can be afforded your 'hammer-holding' hand
while single jacking will help conserve your energy. A wrist
thong may be attached to the end of the handle to help drill
at unusual or difficult angles. The thong is looped around
your wrist and lets you rest your grip a moment after each
stroke. On the backstoke the fingers may be opened and the
grip relaxed, allowing the handle to swing free but
restrained from dropping by the thong. At the end of the
backstroke the fingers close around the handle to prepare
for the next swing.
Old time miner using a single jack equipped with
wrist thong, early 1800's.
4. A hole is drilled because rock is chipped by the
concussion of the bit from the blow of the hammer. Grip the
steel firmly but not tightly during each blow. Hand drilling
produces very little shock in the 'steel-holding' hand. The
holder in a modified double jacking operation will also find
that only a small amount of shock is transmitted from the
blow of the hammer. Always wear gloves while holding, in
case of a glancing blow.
After each stroke, turn the drill about 1/8-revolution;
this is called 'shaking' the steel. Drill steel is usually
octagonal in shape, so turn the steel so the next flat side
faces you. There is a slight recoil of the steel after each
blow, and it is after the recoil that shaking is performed.
Lift the steel slightly before turning. If the steel is not
turned, the bit will sink straight into the cut and jam in
the hole. When shaking, allow your grip to relax slightly
after each rotation. Regain your grip before the next blow.
Difficulty in shaking the steel, especially in 'down'
holes, indicates that the rock dust in the bottom interferes
with the cutting edge of the bit against the rock. With two
hands turning the steel, teams may go for longer periods
before clearing cuttings from the hole. Water is helpful for
removing cuttings from holes.
5. Regularly add small amounts of water to minimize dust
from drilling and keep the drill steel cool and the temper
intact. This keeps particles in 'down' holes in solution so
they won't hinder the progress of the drill. Water creates a
mud that sticks to the steel and is withdrawn from the hole
with the steel. The adhering mud is removed by rapping the
steel sharply against the rock. Holes are periodically
flushed clean by bouncing the steel in the hole while adding
water to create an agitating motion. The generous use of
water allows the drilling action to force cuttings out of
the hole as quickly as they are generated. Minimize
unpleasant splashing by wrapping a small rag around the rod
at the top of the hole. Keep the rag loose so shaking is not
impeded.
Using water in a drilled hole.
Removing cuttings from deep holes may require more water
than is readily available. In this case, small amounts of
water may be used to create the mud, and a long-handled
spoon can extract it. Oldtime miner's spoons were forged
from various lengths of iron rod. They had a handle opposite
a flattened, slightly curved end approximately 3/ inches
wide and up to 6 inches long. These spoons were used for
clearing holes of cuttings and for retrieving sticks of
powder from misfired holes. The pointed tip on the handle
end was used to thoroughly clean holes before loading and to
pack explosives in the holes. Today similar soft metal
"powder spoons", made of 3/8-inch iron rod in lengths up to
8 feet, are sometimes still used in underground mines. We
made a 30-inch long version of the "powder spoon" for trail
work. We also made a spoon from a piece of aluminum tubing
1/2-inch in diameter and about 22 inches long. We flattened
and shaped one end so it had a flat edge roughly
perpendicular to the rod handle. This spoon worked well for
cleaning 1'/-inch holes up to 16 inches deep.
Our version of the miner's
powderspoon had a
30 inch handle and a 6 inch spoon.
The aluminum spoon we made had a 22 inch
handle and a 5/8 inch spoon.
6. Carefully select the points at which holes will be
placed. Use natural points of weakness, and keep in mind
your total breaking needs for the project. Evaluate the site
and proceed accordingly. If you plan to remove a rock
entirely, position the holes as perpendicular as possible to
the largest face parallel to its strata (see
A below). If the rock is to remain in place with only
parts removed, a different technique is used (see
B below).
 |
| A. Drilled holes are perpendicular to the
surface being worked. If wedge and feathers are used
in this instance they will be less likely to be
unduly stressed, because the compression forces of
the rock are more evenly distributed on them. This
rock will probably be split into chunks that will
allow its complete removal. Arrows indicate probable
direction of splitting. |
 |
| B. The drilled hole is not perpendicular to
the surface being worked. Splitting will be both
less predictable and less efficient in this
situation. Be aware also that when you work the
wedge into the hole it will be more prone to bending
or breaking because the compression forces are
distributed unevenly. You have already determined
that only a section of the rock will be removed.
That is what you can expect to happen here. Arrows
indicate probable direction of splitting. |
The same principles can be applied if a prospective trail
tread crosses a rock face.
 |
| A. If the rock looks and feels solid, drill
to remove it completely. |
 |
| B. If the rock is weathered, seamy, or soft,
perhaps you can chip it flat. |
Hand Drilling and Breaking Rock for Wilderness Trail
Maintenance
Breaking Rock
Except when using explosives rock is split or broken by
stressing it beyond its tensile strength. Rock is stronger in
compression than in tension. For example, most rock will support
a heavy load upon it, but can be pulled apart relatively easily.
Moreover, different rocks have different tensile strengths; that
is, some are easier to break than others. When breaking rock,
stress it at points of natural weakness.
Seamy rock will usually break irregularly because it has no
major points of natural weakness. Moreover, holes drilled in
seamy rock sometimes slip because the layers shift both
horizontally and vertically. This causes the steel to jam in the
hole or a feather to be bound on one side against the wedge. You
can best avoid this by carefully placing holes, by keeping them
as straight as possible, and by attempting to determine in
advance what will happen when the rock breaks. Sometimes,
however, a new hole must be drilled to free a jammed steel or
wedge and feather set. Be careful to avoid extra stresses on
jammed tools while working to free them. A knowledge of rock
types will also help you plan the job, procure tools, place the
holes, and will indicate what to expect when drilling.
Rock Types
This manual offers no 'hard and fast' rules about hole
spacing and drilling depth necessary to break specific types of
rock. This information is best gained from experience, depending
on what is encountered and what is required at a job site. The
general categories of rock that follow give broad hints about
what to expect when drilling them.
Soft Rock
- Shale--Clay, mud, and silt that is consolidated
into a finely laminated structure.
- Shist--Crystal line rock with component
minerals arranged in a roughly parallel manner.
Medium Hard Rock
- Sandstone--Sedimentary rock, usually quartz
sand, cemented by silica, iron oxide, or calcium carbonate.
- Limestone--Sedimentary rock that is formed by
the accumulation of organic remains consisting mainly of
calcium carbonate.
- Marble--Metamorphic limestone that has been
crystallized by a pronounced change in heat, pressure, and
water content.
Hard Rock
- Bluestone--Bluish gray metamorphic rock similar
to sandstone.
- Gneiss--Laminated metamorphic rock similar to
granite.
- Granite--Naturally igneous rock formed of
crystallized quartz and orthoclase.
- Basalt--Dense igneous rock that consists of
feldspar and various minerals.
Wedges (Plugs) and Feathers
Wedges and feathers are tools designed to split rock when
driven into a drilled hole or natural crack. The wedge fits in
the hole between two feathers whose flat sides form a guide that
prevents the wedge from jamming as it is driven into the hole.
Use wedge and feathers as follows: Position the feathers in the
hole so the flat sides of the wedge will be parallel to the line
along which the break will occur. Drive the wedge into the slot
between the feathers until the rock cracks, or until it sticks
in the rock. Then tap the wedge lightly back and forth along the
inside edges of the feathers until it is freed. Remove the wedge
and, if necessary, begin again. Proceed slowly to allow the
tools time to do their work.
Correctly placing the wedge and feathers.
To be effective, wedges and feathers must be correctly sized.
The diameter of the wedge rod and feathers at the point where
the rod meets the feathers must exceed the diameter of the hole.
Driving the wedge between the feathers forces them against the
sides of the hole and splits the rock.
Avoid unnecessary stresses on wedges and feathers by drilling
holes as straight as possible. Straight holes help keep wedges
and feathers from binding or jamming in the hole.
Miscellaneous Tips
Drilling and splitting a large rock not free to move when
split calls for additional care. If a hole is placed in the
middle of the rock, one side may shift and jam, bend, or break
the steel or the feathers and wedge. Similarly, splitting a rock
that is supported only at the ends can shear tools if it breaks
and slides suddenly. In instances like these, start holes from
an open edge and work toward the middle. A hole drilled near the
side of a large rock 18 to 24 inches from an edge will indicate
how you should proceed.
Holes drilled in these lateral locations
will be
less likely to jam steel or wedges and feathers
than one drilled in the middle.
Picking
Pick heads have a pointed tip for exposing and enlarging
points of natural weakness in rocks. Many times soft and medium
hard rock can be broken with a pick so that no drilling is
required.
When using a pick, be careful to maintain control of the head
at all times. Avoid raising the pick overhead while swinging.
This wastes energy needed for sustained operation, sacrifices
accurate placement of the tip, and creates a safety hazard for
the operator and others. The narrow heavy pick head cannot be
easily controlled or directed from these heights.
Avoid using the pick as a prying tool; use crowbars instead.
If picking or prying a natural seam does not split the rock, use
a drilling steel or a wedge and feathers in the hole. Always
wear safety glasses or goggles when picking to guard against
flying chips of rock.
Picks are effective tools for breaking rock.
Using a pick.
Maintenance
Conscientious tool maintenance is essential to safe drilling
and increases tool life. Drilling steel must be sharp and tools
must be reconditioned periodically. Pick heads must be kept
sharp, hammer faces smooth, and handles sturdy. Wedges and
feathers should be carefully protected.
Courtesy of the University of Montana
Mansfield Library Archives.
Hand Drilling and Breaking Rock for Wilderness Trail
Maintenance
Drilling Steel
Sharpening
Make sure that your steel is straight. Bent steel is nearly
impossible to use effectively and a poorly placed blow could
glance and cause an injury. Keep the steel sharp. Sharp steel
helps you work safely and efficiently.
Use a double cut file or grinder to redress steel that is not
badly worn. Maintain existing edge bevels as much as possible.
In the field file the heads smooth and cutting edges sharp. Use
a completed hole as a holder. Insert the steel upside down and
brace it with your knee or foot. Your partner may also hold the
steel while you file. Always wear gloves when sharpening or
holding.
When using a grinder, remember to avoid excessive heating of
the steel that could draw temper and soften the bit. Be aware
that forged tools are harder on the outside than they are at
their core. Careless or excessive grinding or filing can expose
the core and cause premature dulling.
Using a hole as a holder.
One worker may hold the steel while the other files.
Reconditioning and Tempering
The facilities and expertise of a blacksmith will almost
certainly be required to completely recondition dull drilling
steel. Here is an historical account describing how a blacksmith
worked:
"Drills are sharpened, first by forging to the right shape
and to give a sharp edge; this edge, however, by many smiths is
not hammered sufficiently sharp, and they use either a file or a
grindstone to give the required edge. The point is then heated
to a glowing red and dipped in cold water for a few seconds to
harden the steel; the edge is then rubbed on sand to clean it.
The smith examines for the colour, and dips at a pale straw
colour to make it hard, or at a dark blue, which makes it a
little tougher. If, after the first cooling, there is not
sufficient heat in the drill for these colours to show on the
edge, it must be reheated in the fire. When the drill is dipped
for tempering, it may remain in the water till cold. The exact
colour at which steel has to be dipped varies with the quality
of the steel, and also, no doubt, with the nature of the work,
but a little practice will soon show." (Lupton, 1906).
Special variations in the temper and length of steel were
sometimes required to drill particularly hard rock.
Modern hand drilling steel has similar forging requirements.
In the reconditioning process it is important for the blacksmith
to be able to control the hardness of steel by tempering. In
general, the harder the steel, that is, the more cohesive the
particles of metal, the more resistant the tool will be to wear.
If the steel is made too hard, however, it may become brittle
and break during use.
Standards for the hardness of tempered steel have been
established that guide smiths to the correct hardness for a tool
based on its usual range of applications. Hardness is measured
by pressing on tempered surfaces with specific shapes under a
known pressure. The amount of pressure that the tempered metal
is able to withstand before an indentation is made becomes a
measure of its hardness. The best known measures of hardness of
tempered steel for tools are Rockwell and Brinell hardness.
Rockwell hardness tests measure the indentation of a diamond
cone (Rc), or a steel ball of a specified diameter (Rb), on a
tempered surface. Brinell hardness tests measure only with a
ball (HB) (see
Hardness Testing Conversion Table).
The steel on the tool's surface is slightly harder than the
steel in the middle. This is because during the quench the
particles on the surface are more radically affected; they are
more cohesive than those in the middle or slightly beneath the
surface. The key to tempering is to retain the desired toughness
at the center of the tool. The softer core assures a strong
tool, while the hard exterior provides the cutting edge or
protective shield.
Complete Reconditioning
Here is a description of a modern tool reconditioning
process:
Forging
- Heat the point to a yellow color (1800 to 1900°F/982 to
1038°C), for the length necessary to forge. Be careful not
to heat too far back on the steel; this is the most common
cause of premature breaking after reconditioning. Do not
attempt to forge below a cherry red color, (1450°F/790°C)
(see
Incandescent Colors and Temperatures chart).
- Rework tools only to their original design.
- After forging allow the tool to cool to room
temperature.
Hardening
- Reheat the point to a cherry red color 1 1/2 to 2 inches
back from the cutting edge, making sure to overlap the
forging depth
Quenching
- Quench in water, or in a brine or oil solution. Maintain
the quench at a temperature of 75 to 100°F/24 to 38°C, to
achieve Rockwell hardness (Rc) 60 to 65, Brinell hardness
(HB) 600 to 652
Tempering
- Withdraw the tool from the quench with sufficient heat
remaining in it to draw the temper. A shade of brown or dark
yellow is best.
- Rub the point clean with emery.
- When a light straw color appears, (430°F/222°C),
complete the quench.
- If drawing facilities are available, reheat to 425°F/
218°C, and hold for 1 hour to achieve Rc 56 to 60, H B 555
to 600.
Miscellaneous Tips
- Temperatures will vary among types of tool steel.
- This operation should be undertaken only by or under the
close supervision of an experienced blacksmith who knows the
specific requirements of the steel he uses.
- Wear adequate protective clothing, including eye
protection and gloves, at all times.
If your drilling steel includes short 'starters' and longer
'seconds', the smith should make the cutting bits diminish
slightly in width as the rods increase in length. This is
necessary to prevent jamming when a new length of steel is
started in the hole. A drilled hole gradually decreases in
diameter as the tool wears. The bore-hole is not a true
cylinder, but the frustum of an elongated cone. If the head of
the steel becomes mushroomed from extended use, it should be
reshaped by the blacksmith during reconditioning.
The bore-hole is not a true cylinder,
but the frustum of an elongated cone.
Defective Steel and Prolonged Safe Use
Although drilling steel is designed to perform in demanding
applications, few products are subjected to more stress in
service. Hand-hammered percussion tools for drilling and wedging
must endure the same punishment as the rock being worked, so
some failures may be expected.
Defective steel is likely to fail early on due to the severe
stresses from the blows of the hammer, although some break after
considerable service without having been defective. To insure
long life and safe use of drilling steel, avoid these common
causes of premature failure:
- Using steel for an unintended purpose. Prying with the
steel, for example, will bend it and render it unsafe and
ineffective.
- Allowing steel to overheat in service. This will draw
temper and cause cutting edges to soften and dull.
- Failing to keep the steel sharp. This causes extra
stress on the rod.
- Redressing steel inadequately or improperly. Tools
improperly forged and rehardened or excessively filed will
dull quickly, mushroom prematurely, and break before giving
a full measure of service.
Drilling Hammers
Using hammers with cracked handles, loose heads, or chipped
faces is a safety hazard as well as a reflection of poor
maintenance. Examine handles to insure that they are tight on
heads and free of cracks. If handles have been poorly maintained
or neglected, take time to repair or replace them before
beginning a drilling job.
Striking faces should be smooth and evenly worn. Drilling
hammers have hard tempered faces designed to strike softer
drilling steel heads. The head of the steel mushrooms and the
hammer face remains smooth. If a hammer face becomes pitted or
chipped, however, carefully grind it smooth. Work slowly to
avoid damaging the shallow temper of the face. Discard badly
worn hammers. Some hammers have faces tempered soft to mushroom
with use. These allow workers to safely hammer hard metals
without the hammer face chipping. Mushroomed hammer heads can
also be reconditioned by a blacksmith.
Wedges and Feathers
Wedge and feather sets should generally be treated like
drilling steel. Avoid using wedges alone to break rock. Wedge
tips are not tempered hard enough to start holes. Hammer wedges
primarily on the heads, and avoid striking feathers as much as
possible. Remember also that wedge and feathers break rock with
friction and stress, so overheating can occur.
Picks
When sharpening picks grind the tips to a point 1/8-inch
square. This will make a sharp, effective point that is strong
enough to resist breaking. Before sharpening secure the head in
a vise or special jig. Sharpen with an electric grinder or a
10-inch mill bastard file. Badly damaged picks can also be
reforged by a blacksmith.
An oval-tapered eye and handle allow pick heads to tighten
when swung, while remaining removable for sharpening,
transporting, and handle replacement. A small screw in the
handle just below the head will further fasten heads to handles.
Pick secured for sharpening without a vise.
Hand Drilling and Breaking Rock for Wilderness Trail
Maintenance
Sources of Supply
Drilling Steel
1. Senter Tool Service, Portland, Oreg., manufactures hand
drilling steel and others tools to individual specifications.
The steels are generally one-piece units with a sharpened edge
for drilling and a head for receiving the blow of the hammer.
The cutting edges can be made in various styles, although star
pattern bits are most common. The steels can also be made with
removable bits if a rod of greater than 1-3/8 inches is ordered.
The latter may be larger than necessary for most trail work, but
detachable bits may be preferred in some situations. Senter Tool
Service maintains a complete blacksmith shop, so all types of
steel can be returned to them for reconditioning. Used steel
that is sometimes available in second-hand stores can also be
reconditioned there. In addition they will manufacture hammers
to your specifications, along with a large variety of other hand
tools not commonly found on the market.
2. Local blacksmith shops are usually equipped to manufacture
and recondition drilling steel, and although they may not
routinely fill orders for hand tools, they are often willing to
help.
Courtesy of the University of Montana Mansfield Library
Archives.
Drilling Hammers
General Services Administration
(branch office)
Local hardware stores
Senter Tool Service, Inc.
5413 NE Columbia Blvd.
Portland, Oreg. 97218
(503) 381-1151
Stanley Tools
(Div. of Stanley Works)
Box 1800
New Britain, Conn. 06050
(203) 225-5111
True Temper Corp.
1623 Euclid Ave.
Cleveland, Ohio 44115
(216) 969-3366
Wedge and Feather Sets
ABEMA
Box 775
Norwalk, Conn. 06856
(203) 846-2003
Atlas-Copco Corp.
610 Industrial Ave.
Wayne, N.J. 07652
(201) 696-0554
Senter Tool Service, Inc.
5413 NE Columbia Blvd.
Portland, Oreg. 97218
(503) 281-1151
Picks
Ben Meadows Co.
Box 80549
Atlanta, Chamblee, Ga. 30366
(404) 455-0907
Easco Tools, Inc.
6721 Baymeadow Dr.
Glen Burnie, Md. 21061
(301) 760-2200
Forestry Suppliers, Inc.
Box 8397
Jackson, Miss. 39204
(601) 354-3565
Sears Roebuck and Co.
(local outlet)
Union Fork and Hoe Co.
500 Dublin Ave.
Columbia, Ohio 43216
(614) 228-1791
Warren Group
(Div. of Warren Tool Corp.)
Box 68
Hiram, Ohio 44234
(216) 569-3224
Woodings-Verona Tool Works
Box 126
Verona, Pa. 15147
(412) 828-7000
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