PROCEDURE FOR FABRICATING FIRING DEVICE AND WOODEN BOX MINE

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-02646R000500190001-2
• Release Decision: RIFPUB
• Original Classification: K
• Document Page Count: 51
• Document Creation Date: November 11, 2016
• Document Release Date: July 23, 1998
• Sequence Number: 1
• Content Type: REPORT

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PROCEDURE FOR FABRICATING FIRING DEVICE
AND WOODEN BOX MINE
V
to
0
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PROCEDURE FOR FABRICATING FIRING DEVICE
AND WOODEN BOX MINE
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The purpose of this manual is to provide detailed information
and a step-by-step procedure for the fabrication of all parts, and
assembly of an improvised box mine. All the parts for the firing
device can be manufactured from standard brass stock in a small ma-
chine shop by machinists without special skills. The steel ball is
a standard ball bearing and the steel spring is formed from music
wire. A carpenter can make the boxes of soft wood (white pine, pre-
ferably) with a minimum of tools.
The methods described in this manual are not the only ones pos-
sible; however, they do lend themselves to the production of consi-
derable quantities of the item. A turret lathe will speed manufac-
ture of the parts for the firing device, for example, but a conven-
tional lathe will serve. the purpose very well.
The step-by-step procedures described in detail throughout the
manual are intended to provide all instructions necessary for a
person unskilled in the operation of the various machines and tools
described; a skilled machinist and carpenter will need only the draw-
ings which are furnished. The assembled firing device is shown in
Drawing No. 1. Details of the assembly will be described throughout
the manual.
The function of the firing device is to release a firing pin and
allow it to strike a primer which in turn fires a blasting cap to
initiate the explosive charge contained in the wooden box. When the
firing device is assembled as shown (Drawing No. 1), pressure against
the end of the firing device will compress the firing pin spring and
force the sleeve to slide over the body of the device until the steel
ball is forced out into a hole drilled into the sleeve, thus releas-
ing the firing pin. The compressed spring drives the firing pin down-
ward to strike the cartridge primer.
The wooden box (Drawing No. 2) contains the explosive and also
serves to hold the firing device in position. The box lid is grooved
to weaken it so that the desired amount of pressure will compress
the firing device and explode the mine. The breaking strengths of
various types of wood differ considerably and, if wood other than
white pine is used, it will be necessary to vary the slot depth to
obtain the desired breaking pressure (10 psi).
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The body section of the firing device is that portion on which
other parts are assembled (see Drawing No. 1). It is manufactured
from 16 mm (or larger) round brass bar stock.
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Cutting Raw Material
A suitable length of bar stock is placed in a lathe and the
protruding end turned off square. The material is machined to a
diameter of 12.8 mm for a distance of 38.7 mm measured from the
end (Fig. 1). (See Drawing No. 3). The portion on which threads
are to be cut is machined to a diameter of 16 mm.
Fig. 1. Cutting Raw Material
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Boring
Use a center drill (Fig. 2) to start boring out the center
portion of the body section.
Fig. 2. Center Drilling Body Section
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Drilling Finished Bore Hole in Body Section
Complete to final size by using a 9.4 mm straight shank drill
(Fig. 3). The center drill will help align the larger drill for the
finishing operation. The chamfer is made with a drill of larger dia-
meter than the bore.
Fig. 3. Drilling Finished Hole in Body Section
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Cutting the Threads
The body section is threaded (see Drawing No. 3) before it is
cut to length from the bar stock (Fig. 4). The threads must match
those tapped in the cap as the two are screwed together when the
device is assembled.
Fig. 4. Threads Are Cut on One
End of the Body Section
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Cutting to Length
The body section is now in the shape of a cylinder with threads
cut on one end. Before further work can be done on the body, it must
be cut to the required length (41.7 mm) leaving a thread length of
3 mm. The operation is performed with a parting tool (Fig. 5).
Fig. 5. Parting Off Body Section
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Milling Retainer Pin Slot
Clamp the smooth portion of the body section in a vice and cut
the retainer pin slot (see Drawing No. 3). Use a 2.4 mm end mill
for the operation (Fig. 6).
Fig. 6. Milling Retainer Pin Slot
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Cutting Pressure Release Slots
Pressure release slots, which permit free movement of the fir-
ing pin, are cut in the threaded end of the body section. The opera-
tion is performed with a circular cutting wheel (Fig. 7). Only two
cuts are necessary to obtain four slots when the saw is passed com-
pletely through both sides. The slots are 900 apart.
Fig. 7. Cutting Slots in Body Section
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Drilling Ball Release Hole
The ball release hole is located on the side opposite the re-
taining pin slot and some difficulty may be experienced in properly
positioning and holding the body section for the operation. A jig
made of square stock will make it possible to rapidly and accurately
perform the drilling operation and will be well worth the effort,
especially if several of the firing devices are to be made. Fig. 8
shows the position of the hole in the jig through which a pin enters
to line up the retaining pin slot to assure accurate orientation of
the work.
Fig. 8. Use of Jig For Holding Body Section
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Use of Jig for Holding Body Section
Fig. 9 shows the hole in the jig through which the drill is in-
serted to drill the ball release hole. The wing screw is used to
prevent movement of the body section during the drilling operation.
See Drawing No. 3 for dimensions.
Fig. 9. Use of Jig for Holding Body Section
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III. FABRICATING RETAINER PIN
The retainer pin can be made by using 2.0 mm or larger diameter
round stock material. When parting off the pin to the desired length,
a straight tool may be used which will form a flat head, this is
permissible. (See Drawing No. 4).
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IV. SLEEVE SECTION
The sleeve section of the firing device is that portion of the
device that slides over the body section (see Drawing No. 1). It is
held from rotating and limited in longitudinal movement over the body
section by the retainer pin. When the sleeve section is in the ex-
tended position, the ball release holes in the body and sleeve do not
coincide and the ball holds the firing pin from being forced forward
by the firing pin spring. When pressure is applied to the firing
device, the firing pin spring is compressed and the sleeve is forced
to slide over the body section until the ball release holes coincide,
permitting the ball to escape and releasing the firing pin. In order
for the device to function peoperly, all parts must be accurately
machined.
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Turning and Boring Sleeve
The sleeve portion of the firing device is manufactured much the
same manner as the body section described in Section II. Round brass
stock is turned on a lathe to a diameter of 18 mm and a length of 44.5
mm. (See Drawing No. 5). Bore a 13 mm hole from one end of the piece
to a depth of 38.5 mm. A sleeve, closed at one end and having a wall
thickness of 2.5 mm, will be produced by this operation.
Fig. 10. Boring Sleeve Section
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Cutting to Length
The sleeve is then cut off with a parting tool to a length of
Fig. 11. Parting Off Sleeve Section
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Drilling Holes in Sleeve
Drilling the ball release, vent, and retainer pin holes in the
sleeve can be accomplished more accurately and rapidly with a jig
(Fig. 12). Dimensions for making the jig can be obtained from Draw-
ing No. S.
Fig. 12. Using Jig to Drill Ball Release
Hole in Sleeve Section
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The cap section of the firing device screws on the threaded end
of the body (see Drawing No. 1). Its function is to provide a seat
for the cartridge base and a nipple on which the blasting cap is
crimped (see Drawing No. 6). The threaded connection to the body
provides access to the inner parts of the firing device for load-
ing and preparation for use.
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Turning and Drilling
Brass round bar stock 18 mm in diameter is suitable material
from which to make the cap section. If larger stock is used, turn
it down to 18 mm for the required length. Drill a 3.2 mm hole to
a depth of 25 mm into the center of the end of the bar (Fig. 13).
The 3.2 mm hole is the finished size of the hole through the nipple
part of the cap and will aid in guiding the larger drills when
machining the threaded end of the cap section.
Fig. 13. Drilling Center Hole in Cap Section
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Cartridge Chamber Forming
The cartridge chamber can be machined more accurately and in much
less time by grinding a 12.5 mm drill as shown in Fig. 14. Dimensions
can be obtained from Drawing No. 6. The drawing indicates square
corners where the chamber diameters are reduced, but slightly rounded
corners will not interfere with the functioning of the part.
Fig. 14. Cartridge Chamber Forming Tool
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Drilling Cartridge Chamber in Cap Section
Once the drill point is properly ground, forming of the cartridge
chamber and drilling of the section to be threaded can be completed
in one operation (Fig. 15).
Fig. 15. Drilling Cartridge Chamber in Cap Section
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Cutting Threads in Cap Section
In the preceding operation, the cap section was drilled in pre-
paration for threading. The thread tapped into the cap must fit
that machined on the body section and must extend to the cartridge
chamber so the body will shoulder against any cartridge base placed
in the device. Use a tapered tap of the required size (Fig. 16B)
and finish the thread with a bottom tap (Fig. 16A).
Fig. 16. Tapered Tap (A) and Bottom Tap (B)
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Finishing Threads in Cap Section with Bottom Tap
The threading operation is performed while the material is still
in the lathe (Fig. 17). The tapered tap is used first, then the
bottom tap.
Fig. 17. Finishing Threads in Cap Section with
Bottom Tap
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Machining Nipple on Cap Section
The next step is to turn a nipple on the cap section. A blasting
cap will be crimped on this nipple. The only critical dimensions are
the two diameters of the nipple. If tool steel is ground to form a
cutting tool as shown in Fig. 18, the operation will be somewhat sim-
plified and considerable time saved. Dimensions for the nipple are
on Drawing No. 6. A parting tool is used to cut the finished cap sec-
tion from the stock.
Fig. 18. Nipple Forming Tool for Cap Section
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VI. FIRING PIN
The firing pin is positioned inside the body of the firing device
and fits on one end of the firing pin spring. The pin is held in
the cocked position by means of a steel ball which rests in the "V"
shaped notch on the pin. (See Drawing No. 1 and 7). When the steel
ball is allowed to be released the firing pin is pushed forward by
the spring, thereby, striking the cartridge primer.
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Firing Pin Point Forming Tool
Select a length of 10 mm, round, brass bar stock and turn down
to 9 mm diameter for approximately 30 mm. To obtain uniform points
on the firing pin, grind a tool (Fig. 19) according to dimensions in
Drawing No. 7. Turn the point on the end of the stock.
Fig. 19. Firing Pin Point Forming Tool
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Ball Recess
The ball recess can be cut with tool steel ground in a trun-
cated "V" shape. (Fig. 20).
Fig. 20. Cutting Ball Recess on Firing Pin
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Cutting Shank on Firing_Pin
A shank to fit inside the firing pin spring is turned as shown
in Fig. 21. All dimensions are shown in Drawing No. 7.
Fig. 21. Cutting Shank on Firing Pin
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Firing Pin Spring
The firing pin spring positioned inside the body section and
over the shank of the firing pin can be formed on a mandrel from
spring steel or music wire of the required diameter (see Drawing No.
8). The mandrel on which the spring is wound (Fig. 22) must be
somewhat smaller in diameter than the inside diameter of the finish-
ed spring as it will expand in diameter when the winding tension is
released.
Fig. 22. Starting Firing Pin Spring on Mandrel
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Winding the Spring
The spring is wound by turning the mandrel and holding consi-
derable tension on the wire. A lead of four turns per centimeter
(Fig. 23) while winding will result in a spring of desired shape.
The spring must be wound to a length longer than required since a
portion of each end must be cut off because of distortion caused by
winding.
Fig. 23. Winding Firing Pin Spring on Mandrel
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VII. FABRICATING WOODEN BOX
The wooden box portion of the box mine has three purposes:
(1) to serve as a container for the TNT or other explosives,
(2) to hold the firing device in place and
(3) to provide a means of regulating the weight or crushing
pressure which will explode the mine.
It is preferable to make the box of soft wood such as white pine.
The box is easy to make and the only dimensions that are criti-
cal are the depth of the slots in the box lid and the drilling and
positioning of the part containing the recess for the firing device.
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Preparation of Lumber
The box is constructed of lumber planed to two thicknesses,
one cm. and two cm., and in widths from 7.5 cm to 16.5 cm. Most
of the box is made up of the thinner 1 cm. lumber. Drawings num-
bered 9 and 10 indicate the dimensions and quantities of each of the
pieces required. Time can be saved if the lumber is planed and cut
to size for a number of boxes before assembly (Fig. 24).
Fig. 24. Dressing Lumber to Desired Thickness
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Cutting Grooves in Box Lid
Grooves are cut in the box lid (see Drawing No. 9) to control
the crushing pressure necessary to actuate the firing device. The
depth of the groove must be determined experimentally for different
types of wood in order to obtain the desired crushing pressure. Soft-
wood is more desirable because the crushing pressure required is us-
ually lower. The grooves are cut with a bench saw (Fig. 25). The
correct spacing of the grooves is obtained by proper adjustment of the
saw fence. The depth of the groove is obtained by adjustment of the
depth of cut. Note that the cross grain cut is deeper than that along
the grain. The width of the cut is not critical and normal "set" in
the saw will produce the desired results. The square "cut out" in
the center of the lid is accomplished by cutting two "V" segments from
each of the two pieces of the lid before they are nailed to the box,
(see Drawing No. 10, Part No. 4).
Fig. 25. Cutting Groove in Box Lid
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Drilling Firing Device Recess
The firing device is held in position by a 2 cm thick wood
support nailed inside the box. (See Drawing No. 10, Part 5). A
recess is drilled in the center of the block to receive the firing
device. By making a jig the hole can be rapidly located and drill-
ed as shown in Fig. 26. Note that the jig has been clamped to the
drill table and pieces to be drilled need only to be fed into the
jig.
Fig. 26. Counter-Sinking Firing Device Recess
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Assembly of the Box
The box is nailed together with small nails approximately 0.1 cm
in diameter and 3 cm long. The firing device support must be nailed
in place before the lid is nailed on. The nails in the lid should
not be completely driven until the explosive is in place. The spacing
of the support is critical (6.2 cm from the top and 8.4 cm from the
bottom) and can be done quickly and easily by use of a gauge block as
shown in Drawing No. 11. See Fig. 27 for method in which gauge block
is used.
Fig. 27. Using Wooden Gauge to Position Center Partition
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Assembly of Pressure Plate
The pressure plate, Drawing No. 10, Part 8, is assembled by
nailing the parts together as shown. The positioning of the 6.5 cm
block in the center of the pressure plate controls the positioning
and orientation of the pressure plate relative to the grooves in
the box lid. The block can be accurately and rapidly positioned by
use of a template (Fig. 28). When placed on the box lid with the
block in the cut out section of the lid, the pressure plate will
cause the lid to break at the prepared slots when sufficient press-
ure is applied, and cause the firing device to function.
Fig. 28. Nailing Small Wooden Block on Pressure Plate
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Loading the Box Mine with Explosives
The mine is shown in Fig. 29 and
using uncut 1/2 and 1 pound blocks of
quence and arrangement by layers.
a cap well must be positioned beneath
blasting cap well is provided in each
30 filled to maximum capacity
TNT. Both figures show se-
each case one TNT block with
the firing device recess. A
TNT block. The blasting cap is
crimped onto the firing device and passed through the wooden parti-
tion and then into the TNT cap well while positioning the device in
the mine. Whether using the 1/2 or 1 pound blocks, trim down to the
proper size so that they may pass beneath the wooden partition in the
mine. To insure detonation of the mine, the blasting cap should be
entirely surrounded with explosive in this manner.
Loading Box Mine with 1/2 lb TNT Blocks
Fig. 29A. First Layer
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IN.
Fig. 29B. Second Layer
r"?hY
YY, W`f n. yE t '4`.=sue -8 F ~?`*
Fig. 29C. Third Layer
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Loading Box Mine with Combinations of 1/2 & 1 lb TNT Blocks
Fig. 30 A. First Layer
Fig. 30 B. Second Layer
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Fig. 30 C. Third Layer
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Cutting Cartridge with Tubing Cutter
The cartridges from most rifle and pistol ammunition can be
readily cut by a tubing cutter. If a hacksaw is used, be sure to
file off rough edges on the cartridge primer before inserting into
the firing device (Fig. 31). Removing the rough edges will help
provide for a better fit into the device.
Fig. 31. Cutting Cartridge with Tubing Cutter
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Sealing Cartridge Primer Aperture
Cartridge primer aperture should be covered with a small piece
of masking tape to prevent moisture from coming into contact with
the initiating charge (Fig. 32).
Fig. 32. Cut Cartridge Primers
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Components of Loaded Firing Device
Figure 23 shows the various components of the loaded firing
device.
Fig. 33. Components of Firing Device
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Placing Cartridge Primer Into Cap Section
Place the cartridge primer into the firing device and then
seal the space around the cartridge with a waterproofing compound
(Fig. 34).
Fig. 34. Placing Cartridge Primer into Cap Section
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Crimping on Blasting Cap
When crimping the blasting cap onto the cap section, place them
both between the thumb and index finger as in Fig. 35. Slight pres-
sure applied by the index finger will allow a snug fit against the
cap section. After crimping, cover the joint with waterproofing
compound.
Fig. 35. Crimping on Blasting Cap
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Assembling Firing Device
Caution: When screwing the cap section onto the body section,
be careful not to apply undue pressure along the longitudinal axis
of the firing device. Sufficient pressure may cause the device to
discharge (Fig. 36).
Fig. 36. Assembling Firing Device
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Placing Firing Device into Box Mine
Caution: Do not force the device into the firing device re-
cess as undue pressure may be sufficient to function the device there-
by setting off the mine (Fig. 37).
Fig. 37. Placing Firing Device into Box Mine
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Checking Firing Device Clearance
This clearance should be between 3 mm to 6 mm. The clearance
can be checked by simply placing a lid section over the top of the
mine box before it is fastened on (Fig. 38).
Fig. 38. Checking Firing Device Clearance
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Positioning Pressure Plate
Place the pressure plate into position over the box mine after
the lid sections have been nailed down. A quick check should be made
to insure that the pressure plate is not touching the firing device.
If there is a gap between the plate and box lid, then the plate
is resting on the device. This condition is dangerous. It must be
corrected because it makes the mine unduly sensitive so that it may
be accidentally detonated while being covered with soil.
Fig. 39. Positioning Pressure Plate
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Checking Ground Level Distance Above Pressure Plate
To measure depth of the mine below ground level, clear the loose
dirt from around the hole (Fig. 40). Then lay a straight board (or
something straight to measure from) across the top of the hole and
measure the distance between the top of the pressure plate to the
board.
Note: The pressure plate must be on the box mine to obtain this
depth measurement.
Fig. 40. Checking Ground Level Distance Above Pressure Plate
Approved For Release 1999/09/07 : CIA-RDP78-02646R000500190001-2