SUMMARY REPORT ON TASK ORDER NO. AA

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-03645A000200010001-4
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 35
• Document Creation Date: December 22, 2016
• Document Release Date: May 25, 2011
• Sequence Number: 1
• Publication Date: December 31, 1958
• Content Type: REPORT

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14-11 MI,
82
SUITAIiMARY REPORT
ON
TASK ORDER NO. AA
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t~ ~tt'Q'"ff~f 11 -! i
April 28, 1959
Enclosed is the Summary Report on Task Order No. AA that
describes the activity under this Task Order from May 1 through
December 31, 1958.
As a result of this activity, a variety of cutting tools
have been evaluated and found suitable to some degree for slotting
brick and marble. Also, design parameters related to an implement
for slotting brick and marble were studied, and the requirements of
a suitable slotting implement were generally defined. This feasi-
bility study did not result in the selection of a specific cutting
tool and power source to perform the slotting operation of interest.
However, the direction of future work to accomplish this purpose
has been defined. The cutting tools evaluated in this program have
been sent to the-Sponsor for further evaluation.
We have enjoyed working on this project and believe that
the effort performed has brought you closer to your goal. We would
appreciate any comments that you or your associates might care to
made in regard to the research under Task Order No. AA.
Sincerely,,,
In Triplicate
! 11 ;" lrl; ~~li
C N
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C
0
SUMMARY REPORT
ON
TASK ORDER NO. AA
OB NO. L-_ 6 3 ~ y~-
BOX NO. -----------
FOLDER MD- ----------
TOTAL DOGS HEREIN /-
December 31, 1958
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Page
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 1
DETAILED SUMMARY . . . . . . . . . . . . . . . . . . . . . . . 2
Investigation of Slotting Methods . . . . . . . . . . . .
Abrasive Blades, and Diamond Wheels and Discs . . . 6
Tungsten Carbide Cutting Tools . . . . . . . . . 8
Air-Abrasive Equipment . . . . . . . . . . . . . . 9
Miscellaneous Tools and Equipment . . . . . . . . . 9
Evaluation of Slotting Tools and Equipment . . . . . . . . 10
Abrasive Blades, and Diamond Wheels and Discs . . . 13
Tungsten Carbide Cutting Tools . . . . . . . . . . . 19
Air-Abrasive Equipment . . . . . . . . . . . . . . . 21
Study of Slotting-Implement Design Parameters . . . . . . 23
Description of Test Equipment . . . . . . . . . . . 23
Evaluation of Test Results . . . . . . . . . . 23
General Considerations 26
FUTURE WORK . . . . . . . . . . . . . . . . . . . . . . . . . 27
Diamond Disc . . . . . . . . . . . . . . . . . . . . . . 27
Tungsten Carbide Rotary Cutting Tools . . . . . . . . . . 28
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LIST OF FIGURES
Page
Figure 1. Abrasive Blade, Diamond Wheels and Discs,
and Tungsten Carbide Rotary Cutting Tools
Which Were Investigated . . . . . 11
Figure 2. Electric Dynamometer With Special Table . . . . . . 24
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LIST OF TABLES
Page
Table 1. Slotting Data for Silicon Carbide - Grit
Blades . . . . . . . . . . . . . . . . . . . . . . . 14
Table 2. Slotting Data for Diamond Wheels and Discs . . . . . 16
Table 3. Comparative Slotting-Rate and Noise-Level Data
for Diamond Wheel and Abrasive Blade . . . . . . . . 17
Table 4. Representative Slotting Data for Tungsten
Carbide Rotary Cutting Tools . . . . . . . . . . . . 20
Table 5. Slotting Data for Air-Abrasive Equipment . . . . . . 22
Table 6. Representative Slotting Data From Dynamometer -
Test Table Experiments . . . . . . . . . . . . 25
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SUMMARY REPORT
TASK ORDER NO. AA
December 31, 1958
INTRODUCTION
Task Order No. AA was undertaken on May 1, 1958, directed
toward the selection and evaluation of a cutting tool or combination
of tools that might ultimately be incorporated in an implement to
facilitate the concealment of wire in the interior of buildings. A
device had been developed for drilling holes through masonry-type
building materials under specialized conditions; but, there remains
the problem of concealing the wire in those cases where it must
traverse a room. If a means were available for cutting a slot in
walls, primarily, and also in floors and ceilings, it appears that the
ease of wire concealment would be increased significantly. It is
believed that if a device could be developed for cutting a slot
1/8 inch wide and 5/16 inch deep in brick and marble at a rate of 1
foot per minute, such a unit would be quite useful.
Based on a cursory survey of probably applicable, com-
mercially available cutting tools, it was felt that the best approach
to the development of a suitable implement for slotting brick and
marble satisfactorily was to select first a cutting tool or combination
of tools that was capable of cutting or routing these materials
rapidly, under the conditions of reasonable applied force, power
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requirements, and life expectancy. To provide a basis for such a
selection, it was believed necessary to conduct an evaluation study
of different types of available cutting tools under simulated-service
conditions. Such a study was also expected to provide information on
the design parameters pertinent to the development of a suitable
slotting implement; the parameters of particular interest were con-
sidered to include slotting rate, rotational speed, pushing force,
and power requirements.
In accordance with the above thoughts, the objective of the
Task Order No. AA research program was to conduct research directed
toward the selection and evaluation of a cutting tool or combination
of tools for use in cutting grooves approximately 1/8 inch wide by
5/16 inch deep in brick and marble at a rate of about 1 foot per
minute without the application of water as a lubricant and flushing
medium. This report summarizes the research performed under Task
Order No. AA, during the period May 1 through December 31, 1958.
DETAILED SUMMARY
The investigation was begun by surveying the cutting tools
and equipment employed in the stone-cutting industry and construction
field. It was learned that abrasive blades, diamond wheels, tungsten
carbide cutting tools, pneumatic tools, air-abrasive equipment, and a
number of miscellaneous tools and equipment were utilized depending
on the work material, location, and desired results.
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The abrasive blade, diamond wheel, and air-abrasive equip-
ment are widely used and appeared to show the most promise relative to
the slotting operation of interest. Therefore, these items were
investigated first, and then small tungsten carbide tools were studied.
In the evaluation of the various potentially applicable
slotting tools and equipment, it was found that the abrasive blade
could be used for dry cutting masonry materials; if a 1/3 to 1/2-
horsepower implement were employed as the power unit, a slotting rate
of 1 foot per minute could be obtained in cutting a slot 1/8 inch wide
by 5/16 inch deep. However, the noise and dust associated with the
operation of the abrasive blade were objectionable.
The diamond wheel also cuts various types of masonry
materials without the use of a lubricant; but,this type of wheel is
expensive, easily damaged by heat, and easily broken when used with a
portable power unit. Also, the noise and dust from the operation of
the diamond wheel are comparable with those from the abrasive blade.
The cutting action of the tungsten carbide end mill and
midget bur results in less noise than does the operation of the
abrasive blade, and there is no associated dust problem. However,
these tungsten carbide tools provide a low slotting rate and have a
short life, although these can be resharpened with some sacrifice of
tool diameter.
? The air-abrasive equipment can be used to cut a slot in
masonry materials; but, the equipment necessary to obtain a reasonable
slotting rate is too large and bulky to be feasible for this purpose.
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This was also true of a number of miscellaneous tools, equipment,
and methods that were investigated.
A study was performed on the design parameters pertinent to
a slotting implement which would incorporate a suitable cutting tool.
Appropriate measurements made by means of an-electric dynamometer
and special test table showed that a slotting tool would require from
about 1/3 to 1/2 horsepower and an average pushing force (on the
workpiece relative to the tool or vice versa) of approximately
5-1/2 pounds in order to cut a 1/8-inch-wide by 5/16-inch-deep slot
in marble at the rate of 1 foot per minute. A similar slot could be
obtained with less power, dust, and noise by cutting two parallel
narrow slots appropriately spaced; if the intermediate material did
not break out in the normal course of slotting, as is frequently the
case, then the material could be removed by means of a simple hand
tool.
Based on the limited number of tests on a wide variety of
cutting tools and equipment, the following recommendations are directed
toward the potential development of a useful slotting implement. A
device comprising two small, thin diamond discs spaced apart on a
spindle, a vacuum dust-recovery system, and a power unit represents
a promising implement; in the development of such a device, additional
effort would have to be performed in studying disc sizes and different
types of bonding agents in an attempt to increase the life and re-
duce the cost of the diamond disc. The tungsten carbide midget-bur
and end-mill rotary tools are also promising items for use in the
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implement of interest; to exploit the advantages of these tools,
some additional research would have to be performed on flute design,
cut, and operating speeds in an effort to increase slotting rate and
tool life.
The various cutting tools and appropriate adapters were
sent to the Sponsor for further evaluation. Based on our findings,
additional research is suggested that would be directed toward the
further evaluation of selected cutting tools and the application of a
suitable power unit, in order to provide the basic components of an
appropriate implement for use in performing the desired slotting
operation.
ENGINEERING ACTIVITY
The engineering activity on this research program comprised
an investigation of commercial slotting methods, an evaluation of
commercial slotting tools and equipment, and a study of slotting-
tool design parameters. Also, consideration was given to recommenda-
tions directed toward the potential development of a useful slotting
implement.
Investigation of Slotting Methods
An investigation of the methods used in cutting, carving,
and slotting masonry-type building materials resulted in the study of
the various tools and equipment. These included abrasive blades,
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diamond wheels and discs, tungsten carbide cutting tools, air-abrasive
equipment, and a number of miscellaneous tools and equipments.
Abrasive Blades, and Diamond
Wheels and Discs
A preliminary investigation of the stone-cutting industry
and the construction field showed that abrasive blades and diamond
wheels are widely used in the cutting and finishing of marble.
Abrasive blades are also frequently employed in special equipment de-
signed to cut brick and to slot concrete. The abrasive blades and
diamond wheels involved in this type of work are generally 12 inches
or more in diameter, are used with a water lubricant, and are de-
signed to cut specific materials. The initial cost of a diamond
wheel is considerably more than that of an abrasive blade; but, with
proper care used in,applying the diamond wheel, this difference in
cost is offset by increased life. The abrasive blade can be used in
the dry cutting of masonry-type materials; under dry cutting con-
ditions, the life of the, blade is reduced. However, the diamond
wheel is not recommended for dry cutting operations unless an ex-
tremely short wheel life is acceptable.
Abrasive blades are manufactured commercially from a
variety of abrasives and bonding materials; these determine.the blade
characteristics of softness or hardness and the resulting wear rate
of the blades when used for specific materials and particular cut-
ting and/or machining operations. In general, a soft abrasive blade
is recommended for working on hard material, and a hard blade for
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soft material. The operating speed for an abrasive blade depends on
the type of bonding agent involved, but is usually within the range
of 5,000 to 10,000 surface feet per minute (sfpm).
Two types of general-purpose blades are manufactured for
use with portable equipment in working on masonry-type materials.
These blades consist of a silicon carbide grit bonded with a resinoid,
and an aluminum oxide grit bonded with rubber; they are 6 to 10
inches in diameter, and have a glass-fiber matt bonded to the surface
or molded in, as a safety measure to prevent disintegration of the
blade if breakage should occur during the cutting operation.
Diamond wheels suitable for slotting operations are manu-
factured in standard sizes ranging from 3 to 24 inches in diameter
and consist of natural diamonds in a variety of grit sizes and con-
centrations, and various bonding agents. Three general types of
construction are normally used in these diamond wheels: (1) the
diamonds are in a matrix bonded to the periphery of a metal disc,
(2) the diamonds are retained in radial slots spaced around the
periphery of a metal disc, or (3) the diamonds are bonded to segments
which are mounted around the periphery of a metal disc. Also, small
diamonds are bonded to the surface of small-diameter metal discs
which are employed in the dental field to cut ceramic materials.
Such discs are particularly useful for slotting operations on or for
cutting precious material where waste must be minimized.
The manufacturers recommend the use of water or a lubricant
with the diamond wheels because the heat generated during dry cut-
ting is likely to destroy the bond and consequently the diamonds
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may be lost from the wheel. Further, diamond wheels with the
diamonds bonded to the periphery are not recommended for use in hand
tools; a twist or binding of the wheel in the slot is likely to
separate the diamond-bearing section from the metal disc. The recom-
mended operating speed for diamond wheels ranges from 6,000 to
15,000 sfpm.
Tungsten Carbide
Cutting Tools
A survey of solid tungsten carbide and tungsten carbide -
tipped cutting tools revealed that these items are used to some ex-
tent in the stone-cutting industry. However, they cannot compete
with diamond wheels and'abrasive blades in production work, except
perhaps in turning operations, because the tool life is short, the
cutting rate is low, and the cost of the tool is high. The tungsten
carbide rotary cutting tools which appeared to be suitable for slot-
ting operations were of two general types: (1) the end mill or the
midget bur, either of which could be used in a router-type operation,
and (2) the slitting-saw-type cutter which could be mounted on the shaft
of a drill motor or similar portable implement. These rotary cut-
ters are designed to operate at high speeds, and lubrication of the
tools is important in order to achieve reasonable tool life. These
tools can be resharpened after they have become dull; however, as a
result, the diameter of the tools would be decreased and narrower
slots would be cut.
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Air-Abrasive Equipment
The stone-cutting industry employs impact-type cleaning
equipment to remove material from the surface of masonry-type
materials. In stone-cutting plants, stationary equipment is used to
cut grooves in the form of letters, numbers, and borders in stone
work; portable equipment is used to do the same job in the field.
Aluminum oxide grit or sand, suspended in air at 80-psi pressure,
constitutes the abrasive and propellant. The grit size and composition,
and the-nozzle diameter vary in accord with the type of material to
be worked and the quality of cut desired. The contour of the slot is
achieved by masking with a resilient material, and the depth of cut
is controlled by varying the rate and uniformity of movement of the
nozzle.
Similar equipment was found to be used in the dental field
and in specialized commercial operations where very fine cuts are
required. Cylinder nitrogen gas is used to propel an aluminum oxide
abrasive, and the amount of material removed is kept to a minimum.
The nozzle and grit sizes are varied depending on the type of cut
desired and the type of material being slotted.
Miscellaneous Tools and
Equipment
In addition to the survey of stone-working tools described
in the previous section, consideration was given to the use of
several miscellaneous types of tools and equipments, in an effort to
uncover other methods which might prove to be applicable to the
ll
bd In,(
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slotting operation of interest. These included percussion-type
tools, electro-arc equipment, the plasma torch, acid, and ultrasonic
impact grinding.
The percussion-type tools and the use of ultrasonics were
not evaluated in the laboratory because these were found to provide
a low cutting rate, and also the associated equipment is large,
bulky, and expensive. The plasma torch with a flame temperature of
between 15,000 and 30,000 F probably could be used to gouge a slot in
masonry-type materials. However, the associated electric-arc-
generating equipment is also large, bulky, and expensive, and conse-
quently this tool is probably not readily applicable. The use of
acid on marble to produce a slot was considered to be impracticable
because this operation would require the application of concentrated
acid over long periods of time.
Evaluation of Slotting Tools and Equipment
On the basis of the information obtained in the initial
investigation of potentially applicable cutting tools and methods, the
following items were selected for evaluation in the laboratory:
abrasive blades, diamond wheels, diamond discs, tungsten carbide cut-
ting tools, and air-abrasive equipment. The various rotary tools are
illustrated in Figure 1. To facilitate the evaluation of these tools,
several types of equipment were used, including a table saw, a
portable heavy-duty power saw, a standard drill motor, a special elec-
tric drill motor (from the Task Order No. 0 drilling unit), an elec-
tric grinder motor, a drill press, and a router.
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Figure 1. Abrasive Blade, Diamond Wheels and
Discs, and Tungsten Carbide Rotary
Cutting Tools Which Were Investi-
gated
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I~~L~ III
Early in the course of those evaluation experiments which
involved the portable above-mentioned power devices and abrasive
blades, or diamond wheels or discs, it was noted that the extent to
which the cutting action was readily controllable depended on the
direction in which the slot was cut in relation to the direction of
rotation of the cutting blade, wheel, or disc. The direction of
rotation of the cutting tools, when attached to these portable imple-
ments, was clockwise as viewed from the implement side of the tool; it
was found that the cutting action of the tools could be controlled
most readily by slotting from right to left. With this relationship
between direction of slotting and direction of tool rotation, the
tool tended to push away from the workpiece; in order to achieve a
slot, the operator had to force the tool continually back against the
workpiece, and,, consequently, by manually varying the force exerted on
the tool, the operator was able to control the cutting action
readily. When slotting from left to right was attempted with the
above-described combinations of portable implements and cutting tools,
the tools tended to "move into" the workpiece and to seize and gouge;
consequently, it was extremely difficult to control the slotting
operation. As a result of this experience, all of the slotting tests
performed with abrasive blades, and diamond wheels and discs were ar-
ranged so that the above-described optimum relationship was maintained
between the direction of slotting and the direction of rotation of
the cutting tool.
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Abrasive Blades, and Diamond
Wheels and Discs
The abrasive blades which were selected for slotting tests
in brick and marble were general-purpose, break-resistant blades
consisting of a silicon carbide grit in a resinoid bonding material;
they ranged from 5 to 8 inches in diameter and were 1/8 inch
thick. Limited slotting tests were made with a blade comprised of
an aluminum oxide abrasive in a rubber bonding material; however, the
results obtained with this type of blade were not so good as those
with the silicon carbide - grit blade. The slotting data presented
in Table 1 were obtained using silicon carbide - grit blades at-
tached to a table saw, a portable power saw, a standard drill motor,
and the motor from the special drilling unit developed under Task
Order No. 0; the slotting operations were all performed dry.
In the above-described tests, the wear of the abrasive
blades was negligible; it is anticipated that this would be so also in
the course of an average field operation. As indicated by the data in
Table 1, with sufficient power available, a slotting rate of 1 fpm
could easily be achieved with this abrasive blade. A 6-inch-diameter
break-resistant blade mounted on a small portable power saw provides
a workable unit. However, the Sponsor indicated that the noise and
dust resulting from the cutting action of the abrasive blade could not
be tolerated under field conditions.
Consequently, a solid wax lubricant and a mist-type spray
consisting of water, a water-soluble lubricant, and air were used
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TABLE 1. SLOTTING DATA FOR SILICON
CARBIDE - GRIT BLADES
Power Unit
Abrasive-
Blade
Diameter,
inches
Slot Dimensions,
- inch
Test
Material
Slotting
Rate, fpm
Table saw, 3/4 hp
7
1/8 wide by 5/16 deep
Marble
2.0
at 3,425 rpm,
?9.8 amp, 120 volt
8-inch heavy-duty power
7
1/8 wide by 5/16 deep
Marble
2.5
saw, 4,500 rpm,
9 amp, 115 volt
6
Ditto
Marble
2.0
Marble
3.0
Concrete
4.5
Brick
8.0
Special drill motor,
8
1/8 wide by 1/4 deep
Marble
0.3
0.1 hp at 2,100 rpm
6
1/8 wide by 5/16 deep
Brick
2.0
6
8
4
1/
wide by 1/
deep
Concrete
1.0
1/4-inch drill motor
5
1/8 wide by 1/4 deep
Concrete
0.3
with saw attachment,
3,000 rpm, 2 amp,
,115 volt
Note: All of the tests were conducted dry.
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with the abrasive blades in an effort to reduce the noise and dust
from the slotting operation. The lubricating and cooling effects
resulting from the use of these lubricants would undoubtedly increase
the life of the blades, but the reduction in noise and in dust was
negligible. Also, when either lubricant was applied in quantity, ex-
cess wax or water was deposited on the workpiece; this would probably
be undesirable under service conditions.
Two general types of diamond wheels were used in slotting
experiments on brick and marble. In one type (Type II), the diamond
matrix was bonded to the periphery of a steel disc, and in the other
type (Type I), the diamonds were embedded in radial slots spaced at
approximately 1/8-inch intervals around the periphery of a steel disc.
Diamond-coated steel discs, 7/8 inch in diameter by 1/32 inch thick,
that are used to cut ceramic material in the dental field were also
evaluated. Although the manufacturers recommend that a lubricant and
a rigid, accurate, spindle mounting be employed when using the diamond
wheel on masonry-type materials, the slotting tests were conducted dry
with intermittent operation of the wheels or discs on fixed spindle
mountings and on portable hand tools. Representative data are
presented in Tables 2 and 3; a few noise-level measurements were made
and are included in Table 3.
The results of the tests using the diamond wheels indicated
that the larger diameter (8 inch) Type II wheels, when run dry at the
recommended speeds, cut the various types of masonry material. How-
ever, it should be emphasized that these wheels must be used intermit-
tently in order to allow for wheel cooling; otherwise, they must be
1LI
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TABLE 2. SLOTTING DATA FOR DIAMOND
WHEELS AND DISCS
Table saw,
3/4 hp at
3,425 rpm, 9.8
amp, 120 volt
8Ainch heavy-duty
power saw, 4,500
rpm, 9 amp,
115 volt
Special drill
motor, 0.1 hp
at 2,100 rpm
Special drill
motor, 0.1 hp
at 2,100 rpm
Electric
grinder motor,
0.1 hp at
22,000 rpm
Special drill
.motor, 0.1 hp
at 2,100 rpm
Slot
Type of Diamond Dimension,
Slotting
inch Material Rate, fpm
8-inch diameter by 1/16 wide by Marble
0.050 inch thick; 5/16 deep
Type II'; grit size Hard brick
100, grit concen- Soft brick
tration 100
8-inch diameter by 1/16 wide by Marble
0.050 inch thick; 5/16 deep
Type II; grit size
100, grit concen-
tration 100
8-inch diameter by Ditto Marble
0.050 inch thick;
Type I
3-inch diameter by 1/8 wide by Marble
1/8_inch thick; 5/16 deep
Type II
2-inch diameter by 1/8 wide by Marble
1/8 inch thick; 5/16 deep
Type II
7/8-inch diameter 3/32 wide by Marble
by 1/32 inch thick; 1/4 deep
2 spaced discs;
grit size 180 to
250
7/8-inch diameter
by 1/32 inch
thick; 2 discs
spaced 3/64 inch
apart
brick
brick
1/8 wide by Marble
1/4 deep
0.30
0.58
4.0
Damaged
by generated
heat; un-
satisfactory
0.10, but
damaged by
generated
heat; un-
satisfactory
Unsatis-
factory;
grabbed and
was erratic
in operation
0.17
0.05
1.20
Note: All of the tests were performed dry; the wheels or discs were operated
intermittently, in an attempt to minimize overheating.
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TABLE 3. COMPARATIVE SLOTTING-RATE AND NOISE-
LEVEL DATA FOR DIAMOND WHEEL AND
ABRASIVE BLADE
Slot
Noise
Power
Type of
Dimensions,
Slotting
Level,
Unit
Wheel
inch
Material
Rate, fpm
db
Table saw, 3/4 hp
Diamond; 8-inch
1/16 wide by
Marble
0.3
91
at 3,425 rpm,
diameter by
5/16 deep
9.8 amp, 120
0.050 inch thick;
volt
Type II; grit
size 100, grit
concentration 100
Abrasive; 8-inch
1/8 wide by
Marble
1.3
99
diameter by
5/16 deep
1/8 inch thick
Note: The tests were conducted dry.
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lubricated during operation. The noise and dust from the action of
the diamond wheels were comparable to those from the abrasive blades.
When operated in a hand implement, these diamond wheels must be
handled very carefully, to prevent breakage of the diamond matrix;
this might occur readily if inadvertently the edge of the wheel were
bound or twisted in a slot. The 8-inch-diameter Type I diamond wheel
was not too "touchy" when used in a hand implement; but, in dry slot-
ting tests, this wheel overheated quickly and was considered unsatis-
factory. In each particular test, the 3-inch-diameter Type II
diamond wheel initially cut, but rather quickly became loaded and over-
heated. The 2-inch-diameter Type II diamond wheel did not slot very
far before it grabbed and became erratic in operation; this wheel also
overheated quickly. On the basis of the results from these tests, the
small-diameter Type II diamond wheels were considered unsatisfactory
for dry slotting masonry-type materials.
The small-diameter diamond discs showed promise; they pro-
vided a fair cutting rate, and caused less dust and noise during slot-
ting than did the larger diamond wheels or abrasive blades. However,
these discs have a very limited tool life, because the bond fails
readily and diamonds are lost from the disc.
The use of an arrangement consisting of two thin diamond
discs appropriately spaced apart on an arbor would result in two thin
slots with intermediate unremoved material. In experimental slot-
ting operations with this setup, the intermediate material frequently
broke out; if not, it was readily broken out with a simple hand tool.
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With such an arrangement, less material is removed than is the case
when a single thicker diamond disc is employed; consequently, it is
probable that a higher cutting rate can be achieved with the spaced
discs, possibly with the use of less power.
The use of a small battery-operated vacuum cleaner was ef-
fective in catching and removing most of the dust resulting from the
slotting operation with the diamond disc. It is of interest that at
least one manufacturer is known to be working on a better bond, in an
attempt to retain the diamonds on the base metal disc and thus in-
crease the life of the diamond disc.
Tungsten Carbide Cutting
Tools
Slotting tests were made in marble with solid tungsten
carbide rotary cutting tools. Representative results are given in
Table 4. The rate data are based on the removal of a specific volume
of material, since in some cases the full depth was obtained by making
two or three cuts in the same slot.
In the application of this type of cutting tool, it is neces-
sary to utilize a router or similar device to provide the means of con-
trol necessary in order to cut a relatively straight slot of uniform
depth. In some of these slotting tests, the router speed was varied
while using a ball-end-mill rotary cutting tool; a speed of approxi-
mately 10,000 rpm seemed to provide an optimum combination of slotting
rate and tool temperature, and, therefore, relatively good tool life.
The noise levels associated with the cutting action of the end-mill-
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TABLE 4. REPRESENTATIVE SLOTTING DATA FOR
TUNGSTEN CARBIDE ROTARY CUTTING
TOOLS
Speed, Slotting.
Power Unit rpm Type of Tool Rate, fpm
Drill press, 2,500 Ball end mill, 4 flutes 0.12
1/3-hp motor
Ditto 2,500 Square end mill, 4 flutes 0.15
it 2,500 Midget bur, 4 flutes 0.8
5,000 Ball end mill, 4.flutes 0.15
.5,000 Square end mill, 4 flutes 0.18
5,000 Midget bur, 4 flutes 0.12
5,000 Ball end mill, 8 flutes 0.20
Router, 5/8 hp 22,000 Ditto 0.18
Ditto , 10,000 it 0.22
Special drill 2,100 Slitting saw, 2-inch 0.06
motor, 0.1 hp diameter by 1/16 inch
thick
Note: All of the, tests were conducted dry on marble, in cutting
the "standard"-sized slot, 1/8 inch wide by 5/16 inch deep.
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and midget-bur-type rotary cutting tools 'were lower than those of the
abrasive blades evaluated. Also, the cuttings remained loose in the
slot, and the dust problem was minimized. The slitting-saw rotary
cutter, however, was -quite noisy and control of the dust was a
problem. This cutter had a relatively low and erratic slotting rate.
These tungsten carbide tools are expensive and the tool
life is relatively short. However, such tools can be resharpened,
with some sacrifice of tool diameter and, therefore, of slot width.
Air-Abrasive Equipment
Two kinds of commercial impact-cleaning type of equipment
were evaluated in slotting tests run in brick and marble. One unit
(No. 1) used aluminum oxide abrasive propelled by nitrogen gas and was
designed for slitting or cleaning small and delicate parts. The
second unit (No. 2) was a shop-type sand-blast apparatus designed to
clean and finish medium-sized machine-shop items. A steel grit pro-
pelled by compressed air is normally used in the operation of the sand-
blast unit, but in our tests in brick and marble, sand was employed
as the abrasive; the brick and marble were masked with resilient
material in order to define the slot width.
The No. 1 unit with a 0.019-inch-diameter nozzle cut a very
narrow slot in brick and marble, and used relatively small amounts of
nitrogen gas and abrasive. However, this equipment was large and the
slotting rate was low. A slotting rate which approached acceptability
was achieved with the No. 2 unit using the standard 1/4-inch-diameter
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nozzle. Representative slotting data obtained with the two air-
abrasive units on marble are presented in Table 5.
TABLE 5. SLOTTING DATA FOR AIR-ABRASIVE
EQUIPMENT
Nozzle Diameter, Slotting
Unit inch Abrasive Propellant Material Rate, fpm
No. 1 0.019 Aluminum oxide, Nitrogen, 0.2 Marble 0.001
0.004 lb/min cu ft/min
No. 2 0.250 Sand, 2.6 Air, 12-1/2 Marble 0.030
lb/min cu ft/min
Based on the information from these slotting tests and the
knowledge that a standard paint-spray electric motor-compressor unit
would deliver 3-1/2 cu ft/min of air at 100-psi pressure, special noz-
zles, 1/8- and 3/32 inch in diameter, were fabricated for the No. 2
unit in an effort to obtain an acceptable slotting rate with less air
and abrasive. Although the air consumption with the 3/32-inch-diameter
nozzle was reduced to approximately 6 cu ft/min, the slotting rate in
marble was reduced to 0.010 fpm. As a result of the low slotting rate
and the apparent bulkiness of a combined' motor-compressor and
abrasive-handling unit, air-abrasive equipment was considered to be
impracticable as a slotting tool.
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Study of Slotting-Implement Design Parameters
A special test table was designed, constructed, and mounted
on an electric dynamometer, to facilitate the study of design parameters
that would be useful in the ultimate development of a slotting imple-
ment. The experimental setup is shown in Figure 2. The design
parameters investigated were power requirements, pushing force on the
workpiece, rotational speed of the cutting tool, and slotting rate.
Description of Test Equipment
The test equipment comprised a spindle for the test blade or
wheel and an adjustable table top to support and guide the test
material or workpiece. The direction of rotation of the spindle was
such as to permit maintaining the previously described optimum relation-
ship between the direction of slotting and the direction of rotation
of the cutting tool (abrasive blade or diamond wheel). In the per-
formance of the experiments, the test material, brick or marble, was
? pushed against the rotating blade or wheel while data pertaining to
the following design parameters were recorded: (1) the force required
to feed the workpiece, (2) the speed of the cutting tool, (3) the
power required to cut a slot 1/8 inch wide by 5/16 inch deep, and
(4) the rate of the slotting operation. Abrasive blades and diamond
wheels were used with this equipment.
Evaluation of Test Results
In general, the abrasive blades and diamond wheels provided
similar results. Table 6 lists representative data obtained with the
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? ? ? # # t O . . . . . . . . . . . . . .
Figure 2. Electric Dynamometer With
Special Table
? . .
? i ! i M ~ ' "
..ruin 'a?'.~?
I j I I
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TABLE 6. REPRESENTATIVE SLOTTING DATA FROM
DYNAMOMETER - TEST TABLE
EXPERIMENTS
Abrasive-Blade
Horse-
Abrasive-
Blade Diameter,
Slotting
Speed, rpm
power
inches
Rate, fpm
1,800
0.3
6
0.3
2,900
0.4
6
0.6
3,000
0.4
6
0.8
3,200
0.8
6
1.1
3,400
o.4
6
1.0
3,400
0.6
6
1.2
3,400
0.8
6
1.7
3,000
0.4
8
1.1
3,400
0.7
8
1.3
3,400
0.6
8
1.8
3,400
0.8
8
2.4
3,400
0.8
8
2.7
Notes: 1. The slot cut was 1/8 inch wide x 5/16 inch deep.
2. The force required to feed the marble test material
into the blade averaged 5-1/2 pounds.
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electric dynamometer and test table using an abrasive blade to cut
a slot in marble.
The test results were comparable with those obtained with
the abrasive blade on hand-operated portable power implements. The
higher surface speeds resulted in higher slotting rates, and also
smoother cutting action of the blade. The data also indicated that,
to obtain a slotting rate of 1 fpm with a tool that removed all of
the material from a 1/8-inch-wide by 5/16-inch-deep slot would re-
quire between 1/3 and 1/2 horsepower. The force required to feed the
work, about 5-1/2 pounds, did not vary appreciably with the different
test materials or blades and also no problem was encountered in feed-
ing the workpiece.
General Considerations
In connection with the ultimate development of a slotting
implement, the speed of the cutting tool used would depend on the type
of tool and material to be slotted. In the tests performed, the
abrasive blades operated at speeds of from 5,000 to 8,000 sfpm pro-
vided satisfactory dry slotting without damage to the blades as a
result of excessive generated heat. However, since the design
parameters are dependent on the amount of material to be removed, it
appears worth while to consider the advantages of minimizing the
amount of material to be removed by employing some arrangement like
the previously discussed setup with two thin diamond discs spaced ap-
propriately apart on an arbor; it is recognized that the uncut
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material remaining between the two thin slots obtained by using such
a setup might. have to be broken out, but this operation could be done
quickly with a simple hand tool. Thus, as a result of decreasing the
amount of material to be cut, it would be possible to reduce the
power requirement and the pushing force, and also the amount of dust
and noise "generated" in the course of the slotting operation.
FUTURE WORK
The results of the findings under this research program
indicate that the factors which would affect the design of a combined
slotting tool and power source are the power required, the rate of
cut desired, the control of the drive, the tolerable level of noise
and amount of dust, and the tool life. On the basis of consideration
of these factors, the diamond disc and the tungsten carbide rotary
cutting tools show the most promise for application in a slotting
implement. It is believed that both of these types of cutting tools
should be investigated further, in an effort to determine which might
be superior for this particular application.
Diamond Disc
If a program were to be undertaken to develop a slotting
implement using the diamond-disc cutter, we recommend that the initial
effort be concerned with working closely with the manufacturer of
diamond discs, in an attempt to develop a specialized diamond disc;
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a desirable diamond disc would be 2 or 3 inches in diameter and would
be produced using an improved bonding agent that would significantly
increase the service. life of the tool. As currently contemplated, it
would be advantageous for the implement of interest to employ two
diamond discs spaced apart on a common arbor so as to cut two narrow
slots. It is likely that the material between these slots would break
out in the normal course of slotting, and, if not, this material could
be removed readily with a simple hand tool, in order to obtain a slot
1/8 inch wide x 5/16 inch deep.
A further investigation should be made to determine the
disc operating speed which would provide for an optimum combination of
slotting rate and tool life. To complete the slotting-implement
development, a small electric motor should be selected for use as the
power unit. Also, it is contemplated that a vacuum-type dust col-
lector should be used with the slotting implement, to facilitate the
removal of the dusty cuttings. This dust collector could either be
an independently operated unit or could be incorporated as an integral
part of the implement. Since the slotting action of the diamond disc
is relatively quiet, it is expected that an electric-motor power
source, two diamond-disc cutters, and a vacuum-type dust collector
could be combined in an implement which could operate at an accept-
able noise level.
Tungsten Carbide Rotary Cutting Tools
In a potential program to develop a slotting implement
using a tungsten carbide end mill or midget bur, we recommend first,
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working closely with the manufacturer of solid tungsten carbide
rotary cutting tools in an effort to obtain a cutter which would pro-
vide an acceptable slotting rate and tool life. In this connection,
the flute design, number of flutes, type of cut, and operating speed
should be investigated because these factors control the cutting
action and the heating up of the tool. It is contemplated that
specialized cutters would be required for this development program.
Subsequently, an appropriate electric-motor powering
implement should be developed or prepared by modifying an available
device; this unit should operate like a router-type tool, so as to
provide the necessary control of slotting depth and direction. The
noise associated with the cutting action of the tungsten carbide
midget bur or end mill would probably be acceptable. Since the loose
cuttings remain in the slot cut by these tools, it appears that there
would be no dust problem. However, if these tools should require high
operating speeds, as was suggested by some of the results of this
initial investigation, then consideration should be given to the de-
velopment of-a sound-dampening system for reducing the operating
noise to an acceptable level.
The cutting tools which were evaluated under this research
program have been submitted to the Sponsor for further evaluation. If
the Sponsor indicates an interest in the development of a slotting
,implement, we shall submit an appropriate proposed program of
research.
(0)[fj)jCridL
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