    [Ordnance Maintenance Compass M2]
    [From the U.S. Government Publishing Office, www.gpo.gov]

    ﻿W 1.35!
    TM 9-1596
    Document Reserve
    WAR DEPARTMENT
    TECHNICAL MANUAL
    ORDNANCE MAINTENANCE
    COMPASS M2
    August 14, 1942
    NON-CIRCULATING
    TM 9-1596
    1-3
    TECHNICAL MANUAL No. 9-1596
    WAR DEPARTMENT, Washington, August 14, 1942.
    ORDNANCE MAINTENANCE
    COMPASS M2
    Paragraph
    Scope______________________________________________________________________ J
    Characteristics____________________________________________________________ 2
    Description________________________________________________________________ 3
    Carrying case Ml 9_________________________________________________________ 4
    Care and preservation______________________________________________________ 5
    Inspection_________________________________________________________________ g
    Maintenance and repair_____________________________________________________ 7
    Disassembly and assembly___________________________________________________ 8
    Painting________________________________________________________________ g,
    Page
    Appendix. List of references____________________________________________ 27
    1.	Scope.—a. This manual is published for the information and guidance of ordnance maintenance personnel. It contains detailed instructions for inspection, disassembly, assembly, maintenance, and repair of the compass M2, supplementary to those in Field and Technical Manuals prepared for the using arm. Additional descriptive matter and illustrations are included to aid in providing a complete working knowledge of the materiel.
    Z>. Information on the packing, storage, and equipment of the compass M2 is not available at this time but will be included in a revision of this manual.
    2.	Characteristics.—The compass M2 is a multiple-purpose instrument used for obtaining clinometer, angle-of-site, and azimuth readings. It is used as a reconnaissance instrument for the Field Artillery. The compass M2 is the standard compass of the Field Artillery. The prismatic compass M1918 is the limited standard item used for the same purpose.
    3.	Description.—The compass M2 (figs. 1 to 3, inch) measures overall about 2% by 1% inches when closed and weighs about 8 ounces. This instrument is made of nonmagnetic materials except the magnetic needle and the needle pivot. Principally, this compass consists of the following major units: A body and related parts, an angle-of-site mechanism and related parts, a magnetic needle with lifting mechanism, an azimuth scale and adjuster, and front and rear sights.
    a. Body and related parts.—The body is provided with a circular glass window held in place by a split retaining ring. This window keeps dust, wind, and moisture from the interior of the instru-
    474308°—42---1
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    FRONT SIGHT	MIRROR	CIRCULAR LEVEL—j	r~ MAGNETIC NEEDLE
    ■ ’ ANGte 0F SrfE L£VEL
    I |U %
    m <~~REAR S5GMT H0LDER
    I	rear sight-5
    ..-x
    IISI ■ 4Tf
    * *	> jr
    *'	v~~ FIXED INDEX
    w •# /
    i_ az I MUTH SCALE
    I— INDEX FOR ANGLE OF SITE SCALE
    NEEDLE LOCKING PIN —J	ANGLE OF SITE SCALE	RA P0 17064
    Figube 1.—Compass M2—cover open.
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    COMPASS M2
    ment and protects the internal parts from possible damage and unintentional adjustment.
    (2) The cover is attached to the body by means of a hinge assembly. The cover contains the mirror, held in position by a split retaining ring. A hole in the cover coincides with the small oval window in the mirror. A black center line is engraved across the face of the mirror.
    • FRONT SIGHT
    ' ' fl
    ■ ■ ■ I •	■	|	'	■	■
    ■ z
    W	COVER
    | ■	r
    ।	RA Pt> 1706 3
    AZIMUTH SCALE ADJUSTER -........>
    Figure 2.	—Compass M2—cover closed.
    The hinge assembly contains an escutcheon pin which serves to parallel the cover with the body when the instrument is fully opened.
    1).	Angle-of-site mechanism and related, parts.— (1) The angle-of-site index is attached to the lever assembly by means of a screw passing through the bottom piece of the compass. The arc-shaped slot in the index provides clearance for the adapter upon which the compass needle is mounted. The center of the circular part of the index is bent slightly upward, which causes the index to press against the bottom piece, creating friction between these parts. This friction prevents the angle-of-site mechanism from moving
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    unless actuated by its lever. The lever is knurled on one end to provide a grip for the fingers of the operator.
    (2)	The level assembly consists of a tubular level vial and a circular level vial inclosed in housings which are sweated onto a bracket. This bracket is fastened to the lever assembly by means of a screw. The circular level is used for leveling the instrument in a horizontal plane and the tubular level is used for leveling the angle-of-site mechanism in a vertical plane.
    (3)	The angle-of-site scale and the four points of the compass represented by three letters and a star are engraved on the bottom piece. The E and IF letters are reversed in order that courses may

    f)
    V	x •’ u"
    Figure 3.	- Site—side view.
    be read directly from the face of the compass. The angle-of-site scale contains 120 equally spaced graduations, each representing 20 mils. The 100-mil graduations are longer than the 20-mil graduations. The 200-mil graduations are longer than the 100-mil graduations and are numbered from 0 to 1,200 in both directions in 200-mil steps.
    c.	Magnetic needle and lifting mechanism.— (1) The magnetic needle assembly consists of a magnetized needle, pointed on both ends, and a jewel housing in the middle. A piece of agate with a cone-shaped depression in its center is mounted in the jewel housing and pivots on the needle of the adapter assembly. This provides a bearing with a minimum of friction. The north-seeking end of the
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    COMPASS M2
    needle is white; the rest of it is black except for the jewel housing. A thin piece of copper wire is wrapped around the needle to balance it (compensate for the dip).
    (2)	The adapter assembly consists of a needle pivot pressed into an adapter which screws into the center of the bottom piece of the compass.
    (3)	A lifting pin is located near the upper left-hand corner of the instrument. The lower end of the pin engages the needle lifting lever and the upper end projects slightly above the body of the compass. The arrangement is such that when the cover is closed the magnetic needle is automatically lifted from its pivot and held firmly against the glass window of the compass.
    d.	Azimuth scale and adjuster.— (1) The azimuth scale is held in the compass body by means of a split retaining ring. Teeth are cut on the under side of the scale to engage with the pin teeth of the adjuster. By means of this arrangement the azimuth scale may be rotated approximately 1,800 mils. The top surface of the scale, painted white, is divided into 320 equally spaced graduations, each representing 20 mils. The graduations, filled in with white, are numbered from 0 to 6,200 mils in 200-mil steps.
    (2)	The azimuth scale adjuster (fig. 4) is slotted on one end to permit rotation by means of a screw driver. The other end is constructed as a pin gear to engage with the teeth cut on the under side of the azimuth scale.
    (3)	The azimuth index is driven into the body through a hole covered by the rear sight hinge. The point protrudes into the interior of the compass and provides the means for orienting the azimuth scale to the local magnetic declination.
    e.	Front aud rear sights.— (1) The front sight assembly is fastened to the body by two screws. When not in use the front sight is folded against the top surface of the cover.
    (2	) The rear sight assembly, fastened to the body by two screws, consists of a rear sight holder and a bracket. The rear sight is hinged to the holder, which in turn is hinged to the bracket. Provision is made for folding the rear sight against the window inside the cover and the cover is closed over it when the instrument is not being used.
    4.	Carrying case M19. -The carrying case M19 (figs. 5 and 6) is a velveteen-lined leather case constructed to fit the general contour of the compass M2. The cover of the case is kept closed by means of a snap fastener attached to the cover. A leather loop, attached
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    on the back of the case, permits suspension of the case from the belt of the user.
    5.	Care and preservation.—a. Cleaning.— (1) The following-cleaning materials are to be used with this materiel:
    (a)	Alcohol, ethyl (for cleaning the glass parts).
    (6)	Solvent, dry-cleaning (for cleaning metal parts).
    (. Care in handling.— (1) Compass M2.— (a) This instrument should be handled carefully to avoid unnecessary shocks. Keep the
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    COMPASS M2
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    compass in the carrying case when it is not being used. After use in wet weather, wipe the compass dry before placing it in the carrying case.
    (&) When the instrument is moved from one position to another or is not in use, the cover should be closed. This lifts the needle off its pivot and prevents injury to the pivot.
    (c) Particular care should be exercised to prevent bending the sights or the cover hinge. Before closing the cover the rear sight
    i-	Jr
    RA PO 17143
    Figure 5.—Carrying case M19.
    should be folded over so that it lies flat on the compass window. If this precaution is not observed, the window may be broken.
    (C
    \\	//	I	EYELET-1	J	_	-----RIVET
    Xs, xX	! I
    -- I  ■'' .s'	I	i’	“*	SHOWN OUT --- ’	n;	OF POSITION J?!		LINING
    LINING	-----n	’
    a	»-i^-Am
    stitching—1	-LINING
    SECTION A-A RAPO 712 2A.
    Figure 6.—Carrying case M19—assembled and sectioned views.
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    COMPASS M2
    rounding air. This moisture, if not excessive, can be removed by placing the instrument in a warm place.
    (/)	lubrication is required for this instrument.
    ( 17140 Figure 9.—-Disassembly of window.
    — SPLIT RING
    WINDOW
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    netic needle by bringing an iron or steel object close to it. Withdraw the object. Note whether the needle swings freely about its pivot and assumes the equilibrium position in a relatively short time.
    ( 17134
    Figure 10.—Magnetic needle, assembly.
    h.	To aline mirror and rear sight.— (1) Hold the compass cover with the left hand, the cover first being opened to lie flat. With a sharp tool in the other hand, pry out the retaining ring (fig. 11). Shift the mirror until the etched line is in correct alinement with the sight tip. Replace the retaining ring by first placing the ends of the ring adjacent to the stop pins and then pressing the ring into its groove.
    (2)	Check the alinement as explained in g above. Repeat the adjustment if necessary. If alinement cannot be secured in this way, either the rear sight or the cover hinge is unserviceable and replacement of those parts is necessary.
    i.	To inspect circular level vial adjustment.—Place the compass on a level surface plate. Note the position of the bubble. If the bubble is not in the central position, adjust the circular level vial.
    j.	To adjust circular level vial.— (1) Remove the compass window by first removing the retaining ring (figs. 8 and 9). Carefully lift out the magnetic needle.
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    COMPASS M2
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    (2) Remove the level assembly by first removing the fillister head screw. Bend the bracket slightly. Replace the level assembly in the compass. With the compass on a level surface, check the position of the bubble. Repeat the adjustment if necessary.
    (3) Place the edge of the compass on a leveled surface and adjust the angle-of-site index in the manner explained in 7(2) below. Reassemble the removed parts in the reverse order of disassembly.
    k. To inspect tubular level vial adjustment.— (1) Open the cover parallel with the face of the compass. Place the edge of the compass
    Figure 11.—Method of removing mirror retaining ring.
    on a fiat, horizontal reference surface so that the angle-of-site index points toward this reference surface.
    (2) By means of the angle-of-site lever, center the bubble in the tubular level vial. Note the indication of the angle-of-site index on the associated scale. If this indication is more than 10 mils, an adjustment is necessary.
    I. To adjust tubular level vial.— (1) Remove the window retaining ring, window, and magnetic needle as explained in 7) (1) and (2) above. Place the edge of the compass on a flat, horizontal surface so that the angle-of-site index points toward this reference surface.
    (2) Set the angle-of-site index to indicate zero on the angle-of-site scale. Loosen the index screw and shift the level assembly until the
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    bubble is centered. Tighten the index screw so that the angle-of-site index lever may be moved without excessive friction or undue looseness. Replace all removed parts.
    m. To inspect alinement of front and rear sights.— (1) Open the compass so that the cover is parallel with the face of the compass. Place the edge of the compass on a flat, horizontal reference surface so that the angle-of-site index points toward this reference surface. Fold the rear sight holder out parallel with the face of the compass and the rear sight perpendicular with its holder. Fold out the front sight so that it is approximately perpendicular to the plane of the mirror.
    (2) Place the edge of a piece of cardboard on this leveled surface next to the sight tips. Accurately draw a horizontal line on the cardboard, passing through the point touched by the tip of the rear sight. The tip of the front sight should also pass through this horizontal line within plus or minus 0.020 inch. Move the rear sight holder out approximately 30°. Again note whether the horizontal line passes through the tips of both sights within 0.020 inch. If the deviation from the horizontal is more than this, an adjustment is usually indicated.
    n. To aline front and rear sights.—Loosen the screws by which the front sight is attached to the compass cover. Move the sight in direction of correct alinement and tighten the screws. If the alinement cannot be secured in this way and if the mirror and rear sight are properly alined, replace the front sight. For disassembly and reassembly procedure of the front sight refer to paragraph 8/ and j.
    8. Disassembly and assembly.—To preserve the parts of the instrument, it is necessary to exercise care and close attention during disassembly, cleaning, and adjustment. To avoid injury to the instrument the proper tools should be used for each disassembly and reassembly job. The extent of disassembly for any certain repair job is determined by the repairman when he makes his detailed inspection.
    a.	To disassemble compass mirror.— (1) Hold the cover firmly in one hand. Insert the blade of a sharp tool or penknife between split retaining ring and mirror near the end of the ring and twist the blade slightly, thus removing the ring (fig. 11).
    (2) Extend one finger or a small blunt object through the window opening in the cover and push the mirror upward (fig. 12). Carefully slide the mirror out. Exercise care to avoid losing the shims underneath the mirror.
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    COMPASS M2
    . MIRROR
    ■	X	MIRROR RETAINING RING
    -
    *’ ' "■ ' ' ' '■> >
    $	'	- I
    ?	wEJjjjN ''
    I" x 1;
    y; - :	;
    X'-;
    RA PD 17142
    Figure 12.—Disassembly of mirror.
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    b.	To reassemble compass mirror.— (1) Remove all old putty from the compass cover. Place a little putty on the upper edge of the cover. Follow the same procedure as for disassembly except in the reverse order.
    (2)	Aline the etched line of the mirror with the rear sight m accordance with instructions given in paragraph 7^.
    c.	To disassemble magnetic needle and related parts.—(1) Remove the split retaining ring by inserting a screw driver blade between the ring and the window (fig. 13). Care should be exercised that the screw driver blade does not slip away from its proper position during this procedure and do injury to the instrument or to the hands of the instrument repairman. Carefully lift out the window.
    (2)	Lift out the magnetic needle assembly and sleeve. Carefully lift up on the needle lifting lever and remove from the compass. Remove the needle pivot from the compass by unscrewing the adapter assembly from the bottom piece. Unscrew the lifting pin bushing. Extract the lifting pin from the compass body.
    d.	To reassemble magnetic needle and related parts.—(1) Replace the needle lifting pin with bushing in the reverse order of disassembly. When replacing the needle lifting lever, make sure that the end of the lever is underneath the lifting pin. To facilitate this procedure, temporarily turn the compass upside down when replacing the lifting lever.
    (2)	Replace the remaining parts in the reverse order of disassembly. When replacing the split retaining ring, put the ends of the ring in the groove first before pressing the ring into position.
    e.	To disassemble level assembly.— (1) Remove the window as explained in . Fire-control materiel :
    Compass M2______________________________________SNL F-219
    Kit, instrument repair__________________________SNL F-206
    Truck, instrument repair, Ml____________________SNL G-92
    Current Standard Nomenclature Lists are as tabulated here.
    An up-to-date list of SNL’s is maintained as the “Ordnance Publication for Supply Index”________________________________________OPSI
    2.	Explanatory publications.
    a.	Cleaning, preserving, lubricating, and welding materials, and similar items issued by the Ordnance Department	TM 9-850
    b.	Fire-control materiel:
    Field artillery fire-control instruments____1___TM 6-220
    Instruction Guide, the instrument repairman_____TM 9-2602
    Compass M2______________________________________TC 22
    c.	Miscellaneous:
    75-mm gun materiel M1897 and modifications______TM 9-305
    75-mm gun and carriage M1917 and modifications-. TM 9-315
    75-mm howitzer materiel_________________________TM 9-320
    105-mm howitzer materiel M1A1 and M2____________TM 9-325
    155-mm howitzer materiel M1917, M1918 and modifications---------------------------------------TM 9-330
    d.	Maintenance:
    Maintenance of materiel in hands of troops______OFSB 4—1
    Special Instructions, Group F___________________OFSB 4-8
    Storage and issue_______________________________TM 10-250
    [A. G. 062.11 (6-18-42).]
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    By order of the Secretary of War :
    G. C. MARSHALL.
    Chief of Staff. Official :
    J. A. ULIO,
    Major General,
    The Adjutant General.
    Distribution :
    R 9 (2) ; IBn 9(1); IC 9 (3) (or 91 medium and heavy maintenance companies).
    (For explanation of symbols see FM 21-6).
    U. S. GOVERNMENT PRINTING OFFICE: 1942
    28
    UNT LIBRARIES DENTON TX 79203
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    1001895664