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Full text of "Description of 3-inch telescopic sights model of 1904"

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No. 1955 



DESCRIPTION OF 

3-INCH 
TELESCOPIC SIGHTS 

MODEL OF 1904 



( THREE PLATES) 



JUNE 15, 1905 
REVISED JULY 15, 1906 
REVISED DECEMBER 5, 1907 
REVISED APRIL 2, 1912 



WASHINQTON 

aOVBRNMBNT PRINTING OPPICE 

1917 



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Wab Department, 
Office of the Chief of Ordnance, 

Washington, Anril 2, 1912. 
This Manual Is published for the information and government of the Regular 
Army and Organized Militia of the United States. 
By order of the Secretary of War : 

William Gbozier, 
Brigadier General, Chief of Ordnance, 
10031—17 

(3) 



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3-INCH TELESCOPIC SIGHTS, 

MODEL OF 1904. 
(Three plates.) 



(The important changes in this pamphlet are shown in boldface type.) 



(The telescopes for these sights were designed by the Warner & Swasey Com- 
pany, Cleveland, Ohio.) 



1. The advantages gained by the use of a telescope in laying a 
piece consist of a decrease in personal error and an increase in power 
of vision. A telescopic sight enables a gunner to see clearly an 
object which is indistinct to the naked eye and to lay a gun on it with 
facility and accuracy. 

2. For the designation of parts see Plates I, II, and III, and the 
list attached hereto giving the nomenclature. Plate I shows a tele- 
scopic sight and cradle with a bracket for a barbette carriage. Plate 
II shows same with arm for a disappearing carriage. Plate III 
shows a sectional view of the telescope. 

Sights for Barbette Carriages. 

8. The principal parts are the telescope (1, 2, 3, 6, 9, 13, PI. Ill), 
the sight bracket (25), the cradle (15), the open sights (4, 16), the 
sight shank (24), the range drum (30), the gear case cover (31), the 
elevating worm (43), the fulcrum (21), the yoke (40), the cables and 
electric lamps, the deflection scales (45), the elevation scale (34), the 
deflection worm (47), and the elevating gear shaft (46). 

4. The sight bracket is bolted to the carriage by means of the feet. 
Tlie cradle is assembled at the forward end to the sight bracket by 
means of the yoke and fulcrum. The yoke shaft seats in the sight 
bracket and is keyed in place ; the fulcrum axes have bearings in the 
two sides of the yoke permitting rotation for elevation and depres- 
sion, and the fulcrum has a short vertical shaft on its underside to 

(5) 



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which the forward end of the cradle is assembled so as to allow rota- 
tion in azimuth only. At the rear end the sight shank is assembled 
between the sight bracket and the gear case cover, being held in place 
by the gear case cover and the elevating gearing. The cradle is 
assembled to the sight shank by means of its head (which is also the 
deflection worm box) and the deflection worm, the latter being 
seated in the box and meshing into a worm segment cut in the cradle. 
The front and rear faces of the deflection box and the head of the 
sight shank are arcs of circles having their common center on the 
axis of the vertical shaft of the fulcrum, and the front and rear faces 
of the sight shank and its seat are arcs of circles having their com- 
center on. the central line of the fulcrum axes. The sight shank stop 
(73) attached to the lower end of the sight shank limits the movement 
of the sight shank in elevation. 

5. The elevation of the sight and the rotation of the range drum 
are accomplished by the elevating gearing, consisting of the elevating 
worm and the elevating gear shaft with its worm gear and spur gear, 
the latter two being on one piece. The elevating worm engages the 
worm gear and the spur gear engages the sight shank rack. The 
piece on which these two gears are cut is mounted on a squared sec- 
tion of the elevating gear shaft, which is also the range drum shaft. 
The range drum is also mounted on this shaft and is held in place 
by the friction of a nut on a washer bearing against the drum and 
the friction of the drum on a shoulder of the shaft. A ribbon spring 
11 feet long and of German silver is secured at one end to the ele- 
vating gear shaft, is wound several times around the shaft, and has 
the other end secured to the gear case cover. The cover is bolted to 
the sight bracket. By rotating the elevating worm, the elevating 
gear shaft is turned, adding to or releasing tension on the spring, 
depressing or elevating the cradle by means of the sight shank and 
rotating the range drum. The spring serves to equalize the force 
required to depress and elevate the cradle. The gear case cover and 
the bracket serve to protect the elevating gearing, the spring, and the 
range drum. The range scale pointer is attached to the cover. 

6. An elevation scale of Grerman silver is dovetailed into the rear 
face of the sight shank, and reads to 6 minutes from zero to 16 
degrees. The pointer is on a piece of German silver dovetailed into 
the sight bracket. 

7. Deflection is obtained by rotating the deflection worm which is 
seated in the deflection woim box and meshes into a worm segment 
cut into the cradle where the box is seated. 

8. The deflection scale, of German silver, is secured to the rear 
end of the cradle and reads to 0.05 of a degree, which equals 3 min- 
utes, over an arc of 4 degrees, beginning with 1 degree on the right 
hand. The 3-degree mark gives no deflection. The pointer plate is 



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secured to a bracket which is screwed to the under side of the sight 
shank head. This bracket has, at the rear end, the deflection lamp 
bracket and a lug that works in a groove in the end of the cradle. 

9. The open sight consists of a peep sight in rear and a cross si^t 
in front, the former mounted on the eye-end telescope clamp and the 
latter on the cross-sight holder. It is for use in picking up an object 
quickly. 

10. Each flight is provided with two small electrio lamps of about 
2 candlepower, and of the following voltages: 110-volt when used on 
disappearing carriages monnted in emplacements with 110 or 220 volt 
mains; 74-volt when used on other than disappearing carriages with 
220- volt mains; and 36-volt when used with 5-inch and 6-inch barbette 
carriages with 110-volt mains. One of these lamps illnminates the cross 
wires, giving bright lines in a dark field, and the other illuminates the 
deflection pointer. They are connected with the electric circuit by the 
cables and plug connections. The lamp that illuminates the cross wires 
is placed in a holder that is secured to the eye end of the telescope tube 
on the right-hand side. Two small mirrors deflect the rays of light 
through two elongated openings cut through the focusing sleeve and 
telescope tube about 90 degrees apart. These openings are so arranged 
that the light from each mirror is thrown upon the full length of the 
wire opposite. The intensity of illumination of the cross wires may be 
varied by turning the lamp bracket diaphragm which has two V-shaped 
openings which pass over slots in the lamp bracket, thereby varying the 
area of the light openings. 

11. The principal parts of the telescope are the telescope tube (9), the 
objective (56), the Porro erecting prisms (55), the draw tube (57), the 
cross-wire holder (53), the focusing sleeve (51), the focusing ring (3), 
and the eyepiece (1, 2, 48, 49, 50, 52). 

12. The telescope tube is the principal piece to which the other parts 
are assembled. The objective is a triplet seated in a cell that screws 
into the forward end of the telescope tube, and gives a 3-inch clear 
aperture. The Porro erecting prisms are two in number, which are re- 
tained in the prism holder by flat springs. Brashear-Hastings prisms 
having cemented surfaces are used in sights Hos. 1 to 26. In sights Hos. 
27 to 297, inclusive, the prism holder and cover are made in one piece. 
In sights after Ho. 297 the cover is separate from the prism holder. 

13. The cross wires are secured to a ring by four clamps, and are 
at right angles to each other. The cross-wire holder (63) is secured 
to the draw tube by screws. The draw tube is assembled to the focus- 
ing sleeve so as to allow longitudinal motion of the former when the 
focusing ring is rotated, and to force rotation of the tube when the 
focusing sleeve is rotated. The sleeve is screwed into the rear end 
of the telescope tube by a thread of tight fit, and will be locked in 
place by a set screw (60). The focusing ring is seated on the focus- 



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8 

ing sleeve by a threaded surface, its motion being limited by the 
telescope tube in front and the focusing-sleeve nut in rear. When 
turned, it transmits longitudinal motion to the draw tube and 
reticule. 

14. Two eyepieces are fumislLed. Each consists of the eyepiece tube 
(50), the field lens (52), the eye lens (49) in its holder, and the eyepiece 
cover (1). The eyepiece tnbe is screwed into the draw tube and carries 
the field lens and the eye lens with its cell, the cover being screwed to 
the latter. There is an amber glass shade in a holder (48), that is 
pivoted so that it may be nsed or not, as desired. It is provided to protect 
the eye from a glare of light. The eyepiece of power 12 should be used 
under conditions of poor illumination. 

15. The front end of the telescope is provided with a movable 
shutter (13) for the protection of the objective. 

16. The clear aperture of the telescope is 3 inches, the focal length 
of objective is 17.25 inches, the magnifying powers of the two eye- 
pieces are 12 and 20 diameters, and the fields are 3.6 degrees for the 
12-power eyepiece and 2.6 degrees for the 20-power. 

17. The image is erect, the erection being secured by the Forro prisms, 
each of which twice totally reflects the pencil of light at an angle of 90 
degrees, so that it emerges parallel to the entering pencil and in the 
original direction. The path of an axial pencil of light is shown on Plate 
m, giving an illustration of the erecting process, in which, however, the 
90-degree angles are not all projected as 90 degrees, because of the relative 
position of the prisms. 

18. The telescope is secured in position by clamps and is located 
by six accurately bored segmental projections, four on the cradle and 
one on each clamp. A locating lug on the front clamp fits into a 
recess in the telescope, thus bringing the vertical wire plumb. 

19. For those carriages in which the gun is carried in a cradle, the 
sight bracket is bolted by means of the feet to seats which form parts 
of the gun cradle. Thus the motion of the bracket conforms to that of 
the gun, and when the sight is properly assembled to the carriage and 
the elevation reading is zero, the optical axis of the telescope and the 
axis of the bore of the gun will remain in parallel planes at all elevations. 
Therefore, if the sight be set at the elevation required for the range of 
the target, and then laid upon it, the gun will automatically receive the 
same elevation. Since the deflection movement of the sight is independent 
of the gun, any deflection necessary may be given to it without affecting 
the elevation. The elevation scale on the sight shank is normally not 
used. 

20. The sight brackets for barbette carriages are lefts and rights. 
Plate I shows a right-hand sight. It is expected that eventually all 
left-hand sights will be removed from 5-inch and 6-inch barbette carriages. 



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Sights for Disappearing Carriages. 

21. The sights for disappearing carriages differ from those for bar- 
bette carriages in that a sight arm is substituted for the sight bracket, 
and a different method of attachment is used. See Plate 11. 

22. The sight arm differs from the sight bracket in shape, has an 
elevation guide, and the feet of the sight bracket are replaced by 
seats for two pins. 

23. All disappearing carriages are constructed for the mounting of 
the 3-inch telescopic sight on the left side of the carriage, except the 
6-inch disappearing carriage, model of 1905. The top of the sight 
standard ends in a horizontal flange surmounted by a cylindrical axis, 
upon which is centered a sight-arm bracket with a flange resting on 
the flange of the sight standard. The sight-arm bracket is forked and 
provides seats for the pins by which the sight arm is attached. The 
sight-arm bracket has a small motion in azimuth and can be set in its 
proper position by lugs and adjusting screws, then clamped by screw 
bolts passing through its flange and into that of the sight standard. 
The method of attachment of the sight to the carriage is more fully 
described in the pamphlets descriptive of the various models of carriages. 

Sights of Nearly the Same Design as the Model of 1904. 

24. There are in service 26 sights, numbered from 1 to 26, both 
inclusive, which are nearly the same as those described above. The 
differences are due to substituting in the latter Porro double reflect- 
ing prisms for the Brashear-Hastings erecting prisms u^d in the 
former. 

25. The telescopes of these sights are differently shaped from the 
model of 1904, being practically symmetrical about the axis; they 
are longer by about 3^ inches, the peep sight is directly over the 
eyepiece, the rear clamp is differently shaped, the sides upon which 
the shutter and clamps are hinged have been reversed, the adjusting 
arrangements for the cross- wire holder are different, and the diam- 
eters of bearings on the telescopes and cradles for seating the tele- 
scope are A ii^ch smaller than on the model of 1904. 

Method of Assembling the Sights and Locating the Pointers. 

FOR barbette carriages. 

26. In assembling the brackets for the barbette carriages, great 
care should be taken to see that the seats are level in both directions, 
and that burrs, paint, and rust are removed from them and the feet 
of the brackets. A small obstruction of this kind will throw the 
sight shank out of plumb. In setting up the bolts, all should be 
brought to a firm bearing before any are set up tight. 



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10 

27. The elevation pointer is marked by the manufacturer of the 
sights, since there is no adjustment for it on the carriage. The ele- 
vation pointer should be cut at the works of the builder of the carriage 
to allow for any possible inaccuracy in the seats and the deflection 
pointer should be put on at the emplacement after the gun is mounted. 

28. After the sight is assembled to the carriage and while the gun 
is at zero elevation the sight should be accurately leveled and the 
pointer cut exactly opposite the zero of the elevation scale. 

29. The position of the deflection pointer may be detennixied by adjust- 
ing the telescopic sight so that its axis intersects the axis of the gon at 
mid range. The pointer should then be set exactly opposite to the 3-degree 
mark on the deflection scale. 

FOR DISAPPEARING CARRIAGES. 

30. The deflection pointer is cut by the manufacturer of the sight, but 
the axis of the telescopic sight and the axis of the bore of the gun should 
be adjusted at the emplacement, so that they intersect at mid range. 
When the sight is in the correct position the bracket should be clamped 
and a light line cut so as to extend over both the flange on the bracket 
and that on the sight standard. 

31. The range drums for these sights will not be used as such, nor 
will they be graduated. The sight shank elevation scales are also not 
used. The movement of the sight in elevation allows for variations in 
the angle of site of the target. 

^ Adjustments. 

32. The cross wires are rendered distinct by screwing the eyepiece 
in or out, and this adjustment has no other object. If the telescope 
is frequently used by the same observer, the eyepiece can be reset 
at the correct position by using the graduations on the outer rim 
in connection with the pointer on the focusing sleeve nut. After 
bringing the cross wires into distinct vision by adjusting the eye- 
piece, the wires may be brought into the focal plane by turning the 
focusing ring until the object appears distinctly and does not seem 
to shift when the- eye is moved from side to side of the eyepiece. 
This adjustment is impossible if the object is too close to the telescope. 

33. The cross wires are mounted on the cross-wire holder, which is 
held in position by four adjusting screws which pass through elongated 
holes in the focusing sleeve. These screws may be reached by first re- 
moving the focusing sleeve nut and unscrewing the focusing ring until 
the slotted screws can be seen through the elongated openings in the 
focusing sleeve. 

34. When adjusting the cross wires the collimating telescope furnished 
with the optical repair kit should be placed in the proper rings and 
securely clamped in the ,sight cradle, and when properly adjusted should 



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11 

be sighted on a target haying plnmb and horizontal lines. The telescopic 
sight is now placed in the cradle with its axis coinciding with the axis of. 
the collimating telescope. 

35. The cross wires shoald be adjusted by means of the adjusting screws 
to coincide with the same plumb and horizontal lines which were seen 
through the collimating telescope. 

36. The slotted holes in the focusing sleeve permit a slight rotary 
motion of the cross-wire holder to secure vertical and horizontal align- 
ment. The focusing sleeve should always be screwed into the telescope 
tube and locked in place with a set screw (60). 

37. The adjustment of the cross wires of the sights numbered from 
1 to 26 is made by unscrewing the focusing sleeve nut and the focusing 
ring until access is given to the capstan head adjusting screws that 
secure the cross-wire ring. These screws should be loosened, the 
adjustment made, and the screws again set up. 

38. To adjust the tension of the range drum spring, run the sight 
shank rack out of mesh, turn the balanced handwheel to the right 
to relieve tension or to the left to increase tension and reengage the 
rack. When the cradle and telescope are in place and the eleva- 
tion is 8 degrees, the force required to rotate the handwheel should 
be the same for both directions. The cradle must first be disengaged 
from the head of the sight shank before this adjustment is made. 

Care and Preservation. 

39. Telescopic sights are necessarily delicate instruments and must 
not be subjected to rough usage, jars, or strains. When not in use, 
the telescope should be kept in its leather case and should be stored 
in a dry place. It should be occasionally examined to insure its not 
being corroded by tannic acid from the case, and all traces of dust 
or moisture should be removed before putting it away. 

40. To obtain satisfactory vision, the glasses should be kept per- 
fectl}' clear and dry. In case moisture collects on the glasses, place 
the telescope in a gentle warmth ; this is usually sufficient to remove 
it. Material issued for cleaning of lenses only should be used^ care 
being taken that the cleaning material does not contain any dirt or 
grit. The glasses will seldom require cleaning on the inside; but, 
when necessary, they should be unscrewed, and by a competent person 
only. The object glass must always be kept screwed home, except 
when removed for cleaning. 

41. The erecting prisms should not be removed from the prism 
holder except by a person with special training in the care of tele- 
scopes^ and if they need repair, report should be made to proper 
authority. Semoval is apt to disturb the adjustment, and finger 
marks or lint will cause difficulty. 



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12 

42. The cross wires ai-e unprotected when the eyepiece is removed, 
and great care must be exercised not to touch them, as they are very 
delicate. No attempt should be made to clean them, except by 
blowing. 

43. The sight bracket (or arm) and cradle should never be removed 
from the carriage unless the carriage is to be dismounted. When not 
in use, these parts should be kept protected by the covers provided for 
the purpose. All bearing surfaces should be kept thoroughly oiled, 
especial care being given to the worm box, sight shank, and bearings 
for the telescope, which are of steel. Care should be taken not to 
remove the oil in putting on the cover. The oil should be wiped off 
before use. The cover should be removed and the sight brackets (or 
arms) , etc., examined at least once in every two weeks, and the cradle 
should be moved in elevation and deflection, so that as much as pos- 
sible of the sight shank and worm box can be inspected. 

No oil should he allowed on the surf aces of the lenvses and prisms. 

44. Special care should be taken in the use of the small electric 
lamps, as they are fragile. Each lamp should seat in its receptacle 
not less than one and one-half turns. 

Dismantling and Assembling. 

45. General instmctions for disassembling and cleaning are g^iven in 
pamphlet No. 1796, Instructions for the Care, Preservation, Bepair, and 
Adjustment of Instruments for the Fire Control Systems for Coast and 
Field Artillery, paragraphs 24 to 28, and 35 to 38, inclusive. 

46. If a sight is packed for shipment, special attention should be given 
to the blocking of it in its packing box to prevent all movement of the 
sight during transit. The telescope should be packed separately. 

47. When ordering spare parts, use the nomenclature given below. 

Nomenclature of Sights. 

(Plates I. II, and III.) 

1. Eye piece cover. 

2. Eye piece dial. 

3. Focusing ring. 

4. Peep sight. 

5. Eye end telescope clamp. 

6. Prism holder. 

7. Deflection worm knob. 

8. Clamp pin. 

9. Telescope tube. 

10. Split pin for clamp pin. 

11. Telescope lamp bracket. 

12. Cell end telescope clamp. 



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13. Objective shutter. 

14. Twisted hook. 

15. Cradle, 

16. Cross sight holder with sight (complete). 

17. Clamping screw. 

18. Yoke cap. 

19. Cross sight screw. 

20. Deflection pointer bracket. 

21. Fulcnim. 

22. Elevating wheel. 

23. Objective shntter handle. 

24. Sight shank. 

25. Sight bracket. 

26. Deflection pointer bracket screw. 

27. Lamp cord. 

28. Plug connection for lamps. 

29. Lamp holder for deflection scale. 

30. Bange drum with range drum scale. 
I»l. Gear case cover. 

H2. Lamp cap. 

33. Telescope lamp holder. 

34. Sight shank elevation scale. 

35. Yoke cap bolt. 

36. Split pin for yoke. 

37. Sight arm. 

38. Deflection scale screw. 

39. Lamp bracket screw. 

40. Yoke. 

41. Focusing nut. 

42. Focusing nut screw. 

43. Elevating worm. 

44. Focusing sleeve nut. 

45. Deflection scale. 

.46. Elevating gear shaft. 

47. Deflection worm and nut. 

48. Amber glass holder with disc (complete). 

49. Eye lens. 

50. Eyepiece tube. 

51. Focusing sleeve. 

52. Field lens. 

53. Cross-wire holder. 

54. Cross wires. 

55. Erecting prisms (Porro). 

56. Objective. 

57. Draw tube. 



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68. Cross-wire holder screw. 

59. Gross-wire clip. 

60. Focnsing sleeve locking screw. 

61. Eyepiece (complete) 12 power. 

62. Eyepiece (complete) 20 power. 

63. Oear case cover bolt and nut. 

64. Prism spring. 

65. Prism holder screw. 

66. Bange pointer (right hand). 

67. Bange pointer (left hand). 

68. Bange pointer screw. 

69. Spring cover. 

70. Spring cover screw. 

71. Bubber hood for 12 power. 

72. Bubber hood for 20 power. 

73. Sight shank stop. 

Wab Depabtment, 

Office of the Chief of Obdnance, 

Washington, April 2, 1912. 
June 15, 1905. 
Revised July 15, 1906. 
Revised December 5, 1907. 
Revised April 2, 1912. 
4513-625-1. 
Form No. 1955. 
Ed. Aug. 24-17-600. 



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