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1. Place the periscope in the V-blocks on the optical I-beam bench. Place it so that sufficient space remains to permit removal of the inner tube.

2. Rotate the revolving grip (3, Figure 6-11) of the left training handle assembly so that the zero line of sight graduation on the index ring (7) corresponds to the stationary index line graduation on the fixed grip (2). This places the head prism at zero line of sight and offers no obstruction for the removal of the inner tube. Check the right training handle for change of power; it should be set for low power.

3. Remove the air outlet plug (14, Figure 4-29) and open the air outlet valve (16) of the

4. Turn the stadimeter handwheel (12, Figure 4-24) to the observing position as noted by the stamped numerals located on the stadimeter housing (8, Figure 6-8). The figure 15 on the height scale dial (13) should appear approximately opposite the value 220 on the range scale dial (14). This makes possible the correct rapid reassembly of the stadimeter housing assembly. Remove the four stadimeter housing bolts (30, Figure 4-24) and take the housing assembly off with care to avoid bending of the stadimeter transmission shaft (12, Figure 6-10). An automatic stop prevents rotation of the stadimeter handwheel (12) when not in place.

6. Remove the focusing knob assembly by taking out four lockscrews (10, Figure 4-39).

7. Remove the rayfilter by pulling outward on both spring actuated plunger knobs (24, Figure 4-40).

8. Remove the eyepiece attachments that are secured to the anchor screw pins (19, Figure 4-29) projecting from the eyepiece box itself.

9. Follow the procedure described under Step 14 of Section 4C1 for the removal of the hoisting yoke assembly.

10. After the nitrogen pressure is released, close the air outlet valve (16) and replace the air outlet plug (14).

11. Follow the procedure of Steps 15 to 19 inclusive of Section 4C1 for the attachment of special fixtures required in the removal of the inner tube.

12. Slowly pull the inner tube sections out of the outer tube until the lower (split) objective lens coupling sleeve (17, Figure 6-7) is clear of the outer tube. The inner tube should be guided parallel with the outer tube and properly centered in it.

13. Place the adjustable roller stand (Figure 4-11) under the eyepiece box (11,Fixture, 4-29), removing the hook of the chain hoist and the shackle.

14. Attach and secure the hinged clamp over the lower (split) objective lens coupling sleeve (17, Figure 6-7). Locate this hinged clamp at the upper part of the coupling sleeve, as shown in Figure. 4-11.

16. Take a light strain with the chain hoist on the lifting spreader bar, and remove the adjustable roller stand. Resume the outward pulling movement slowly until the fifth inner tube section (1, Figure 6-5) is clear of the outer tube. The inner tube should be guided parallel with the outer tube and properly centered in it.

17. Attach and secure another hinged clamp over the upper part of the fifth inner tube section (1). Attach a shackle in the hole of the lifting projection of the hinged clamp, and with the chain hoist hook placed in the shackle, take a light strain with the chain hoist (Figure 4-14).

18. Slowly resume the outward pulling movement of the inner tube, checking to ascertain that it is guided parallel with the outer tube and is properly centered.

19. Transport the inner tube to the V-blocks on the second I-beam bench. Remove both chain hoist hooks, hinged clamps, and steel lifting plate.

20. Remove the outer tube from the V-blocks on the optical I-beam bench with two chain hoists, using canvas covered galvanized cable slings wrapped once around the outer tube in transporting it to the periscope rack.

a. Outer head. The outer head (5) is made of solid forged corrosion resisting steel material. It serves as a covering for the skeleton head assembly and is assembled to the upper part of the outer taper section (1, Figure 6-2).

The lower part of the outer head has a tapered alignment support section with a straight threaded periphery of 32 threads per inch preceding it which fits into a similar internal tapered alignment support and threaded section in the upper part of the outer tapered section.

A mixture of litharge and glycerin is used over the threads to maintain an internal gas and external water seal, thus establishing a permanent joint between the outer head and outer taper section.

The outer head flange is machined at an angle of 8 degrees, with a recess seat to carry a sealing rubber gasket (2) under a head window (4). Above the head window, an additional sealing rubber gasket (1) adheres directly to the beveled edge of the head window and the beveled seat in the head window bevel frame (6).

The normal diameter of the outer head is 1.990 inches and tapers outward on opposite sides to its outer flange face which has a larger diameter. The exterior surface of the outer head upper wall tapers inward with the contour of its flange face surface at an angle of 9 1/2 degrees.

The outer head flange has 16 proportionately spaced tapped holes for retaining the head window bezel frame (6) by means of 16 lockscrews (3) which are inserted in countersunk clearance holes in the head window bezel frame.

b. Head window bezel frame. The head window bezel frame (6) is made of phosphor bronze. Its lower face has a machined irregular recess to fit over the head window (4) with a 45 degrees angle. The 45 degrees angle of the beveled recess accommodates the head window bezel frame rubber gasket (1) which compresses to the angle of the head window (4) to form an airtight joint.

The outer flange of the bezel frame has 16 proportionately spaced countersunk clearance holes to accommodate the lockscrews (3). These lockscrews extend into the tapped holes in the outer head flange (5). The upper side face of the bezel frame is beveled at a 22 degrees angle conforming to its contour, while the lower side face is beveled at a 16 degrees angle also conforming to its contour.

The inner irregular circumference of the bezel frame is beveled at an angle 45 degrees away from the line of contact with the glass to increase the effect of wind in clearing drops of water from the glass and to reduce the lodgement of water

c. Head window. The head window (4) is made of one crown optical glass element with parallel surfaces, and fits into the recess seat in the outer head on a seat gasket (2). It is molded with a 45 degrees angle edge to which a bezel frame rubber gasket (1) is applied. It provides a means of sealing without obstructing the entering light rays, and offers a transparent medium through which light is transmitted.

d. Outer taper section. The outer taper section (1, Figure 6-2) is made of solid forged corrosion-resisting steel. The external diameter at the lowest part is machined for connection to the outer tube (2) in similar manner to the Type II periscope outer taper section. Refer to Section 4D1.

The exterior surface of this taper section starting from the lower undercut part is a straight shoulder for 1/2 inch. From this straight shoulder, it is machined with a radius for a short distance to a diameter of 6 7/8 inches. It tapers upward to a diameter of 1.990 inches in 47 1/4 inches, which it retains for a distance of

The inside diameter of the straight 15 inches is bored for light transmission, leaving a wall of approximately 21/64 inch. The upper part is provided with two counterbored sections. The small counterbored section is tapered to receive the tapered alignment section of the outer head (5), while the large counterbored section is threaded to receive the threaded periphery of the outer head as a permanent joint.

e. Outer tube. The outer tube (2, Figure 6-2) is identical to the Type II periscope. Refer to Section 4D2.

6C2. Disassembly of the head window assembly. The head window assembly is disassembled in the following manner:

1. Unscrew each of the 16 lockscrews (3) evenly, with several threads of each lockscrew remaining in the tapped holes in the outer head flange face (5).

3. After the head window (4) is broken free, release the internal gas pressure and remove the jig.

4. Remove the 16 lockscrews (3), unscrewing them from the tapped holes in the flange face of the outer head (5).

5. Remove the head window bezel frame (6), lifting it away from the flange face of the outer head (5).

6. Remove the head window (4) and the head window bezel frame rubber gasket (1). The head window may stick to the head window bezel frame rubber gasket (1) and the bezel frame (6). Remove the head window bezel frame rubber gasket (1) and destroy it.

7. Remove the head window seat rubber gasket (2) from the recess seat in the outer head (5) and destroy it.

6C3. Cleaning of the outer head, outer taper section and outer tube. The outer head, outer taper section, and outer tube are cleaned in the following manner:

1. These parts should be cleaned after flooding with they use of various sized circular wire brushes and turkish toweling to remove salt deposits, and then blown out with filtered air.

2. Under normal conditions turkish toweling should be used to clean out the outer head, outer taper section, and outer tube.

3. Place a canvas boot over both the outer head and the lower end of the outer tube to prevent any foreign matter from entering the cleaned outer head, outer taper section, and outer tube.

6C4. Reassembly of the head window assembly. The head window assembly is reassembled in the following manner:

1. Scrape the seat in the outer head (5) if necessary, to give the head window a true

2. Insert the new head window seat rubber gasket (2) into the head window seat of the outer head (5).

3. The beveled seat of the head window bezel frame (6) should be scraped if necessary, to provide a true bearing surface in conjunction with the beveled edge of the head window (4).

4. Clean the inner surface of the head window (4) with clean lens tissue, and use a small air bulb to blow off any surface dust.

5. Place the head window (4) in the recess seat in the outer head (5) on the head window seat rubber gasket (2).

6. The head window bezel frame rubber gasket (1) should be approximately 0.031 inch larger than the head window outer irregular circumference, complying with factory drawing dimensions as to thickness. It is placed in the head window bezel frame (6) in one solid piece. A small hole is punched in the center of the rubber gasket to allow trapped air to escape.

7. Place the head window bezel frame (6) with the head window bezel frame rubber gasket (1) over the head window (4). Insert four lock screws (3) in four equally spaced positions in the countersunk clearance holes in the bezel frame, screwing them in tapped holes in the flange of the outer head. Each lockscrew is screwed down loosely, flush with the head window bezel frame.

8. A flat wooden block 1 inch thick and slightly smaller than the inner circumference of the head window bezel frame (6) is placed over the head window bezel frame rubber gasket (1). A C-clamp is placed over the wooden block and the outer head (5) to flatten the raised center portion of the rubber gasket. Use a wooden wedge on the opposite side of the outer head to tighten the C-clamp evenly. The flattening of the rubber gasket forces its outer edges to adhere to the inner beveled walls of the head window bezel frame (6), and utilizes the entire area of the beveled surface of the head window bezel frame to maintain the seal.

10. It is desirable to wet the head window bezel frame rubber gasket (1) thereby offering a lubricant for a brass knife edge when cutting the crude rubber gasket around the inner irregular circumference of the head window bezel frame (6). The brass blade will not scratch the head window surface.

11. Clean the outer surface of the head window (4) in the same manner as outlined in Step 4 of this section.

6C5. Inner tube assemblies. Figure 6-3 at the back of the book shows the inner tube of the periscope which is divided into three telescope systems. Each telescope system is made up of assemblies as follows:

A. Galilean telescope system: Skeleton head assembly.

B. Upper main telescope system.
1. Part I. First, second, third, fourth, and fifth reduced tube sections, and fifth and sixth inner tube sections
2. Part II. Second, third, and fourth inner tube sections.

6. External projections to the eyepiece box.

1. Remove the 10 lockscrews each (5, Figure 4-29) from the left side plate (9) and the pressure gage assembly (21). Unscrew the 10 lockscrews each from the tapped holes in the rectangular recess seats in the left and right sides of the eyepiece box (11). Its may be necessary to tap out two opposite holes located diagonally with an 8-32 tap in the side plate (9) and pressure gage assembly (21) for the insertion of special lockscrews to break the seal of the two rubber gaskets (10). Remove the side plate and pressure gage rubber gaskets and destroy them.

3. Remove each of the four lower shifting wire spindle adjusting nuts (4, Figure 4-28) one by one from each shifting wire spindle assembly, by following the method used under Step 5 of Section 4C1. Carry each of the prism and power shifting racks (43, 44, 45, and 46) to its lower position after removing each shifting wire spindle adjusting nut (4) for the removal of the shifting wire spindle assemblies and each

4. Remove the two lockscrews (27, Figure 6-5) and the removable air line strap (26) from the first reduced tube section (23). Pull the air line section continuation (25) away from the periphery wall of the first reduced tube section (23) to remove the air line section (22) of the second reduced tube section (17) from the air line adapter (20) of the same reduced tube section.

5. Slide the air line section (22) of the second reduced tube section (17) upward, carrying its continuation (25) of the first reduced tube section (23), and its continuation (35) of the sixth inner tube section (28), with its soldered air line coupling (36) from its connection with the upper part of the air line section (37) of the sixth inner tube section. Slide it downward from the three soldered air line straps (39) of the sixth inner tube section, and one soldered air line strap (21) of the second reduced tube section (17).

6. Remove the two lockscrews (40) and the removable air line strap (38) from the lower part of the sixth inner tube section (28). Slide the air line section (37) of the sixth inner tube section upward, carrying its continuation (47) of the fifth inner tube section (41), its continuation (9, Figure 6-6) of the fourth inner tube section (1), and its continuation (21) of the third inner tube section (11) upward. It is carried upward sufficiently to disconnect its soldered air line coupling (20) from the air line section (19) of the third inner tube section (11). Carry the air line section continuation (21) with its soldered airline coupling (20) downward for removal. Slide it out of two soldered air line straps (22) of the third inner tube section (11) and its air line section continuations (9, 47, Figure 6-5), of the air line section (37) from the seven soldered air line straps (10, Figure 6-6) of the fourth inner tube section (1).

7. Remove the two lockscrews (33) and the removable air line strap (31) from the second inner tube section (23). Remove the two lockscrews

8. Remove two lockscrews (22, Figure 6-10) and the removable air line strap (20) from the lower part of the first inner tube section (1). Slide the air line section (16) upward, carrying with it at its lower end the soldered air line coupling (15), disconnecting it from the short bent round air line (14). Slide the air line section (16) and its coupling (15) upward, bending it slightly outward and carrying it out of the soldered air line strap (19) of the first inner tube section (1).

9. Remove the short bent round air line (14), disconnecting it from the undercut section of the long round air line coupling section (13).

10. Unscrew the long round air line coupling section (13) from the tapped hole in the large shoulder flange of the eyepiece skeleton (42, Figure 4-28), sliding it out of the clearance hole in the bearing projection of the spider (2, Figure 6-10).

6D2. Separation of the Galilean telescope system. This procedure is performed in the following manner:

1. Remove the two lockscrews (55, Figure 6-4), unscrewing them from the tapped holes in opposite sides of the upper threaded periphery alignment support section of the fifth inner tube section (1, Figure 6-5), carrying them out of opposite countersunk clearance holes in the skeleton head (1, Figure 6-4).

2. Remove the skeleton head assembly, unscrewing it from the upper threaded periphery alignment support section of the fifth reduced tube section (1, Figure 6-5). Wrap the skeleton

6D3. Separation of the upper telescope system Part I from Part II and Part II from the lower telescope system. This procedure is performed in the following manner:

1. Remove the eight lockscrews (42, Figure 6-5), from the lower part of the fifth inner tube section (41). Unscrew these lockscrews from tapped holes in the upper alignment support section of the fourth inner tube section upper end coupling (4, Figure 6-6).

2. Unscrew the lower part of the fifth inner tube section (41, Figure 6-5) from the threaded periphery of the fourth inner tube section upper end coupling (4, Figure 6-6). Support the reduced tube sections while unscrewing the lower part of the fifth inner tube section.

3. Remove the 15 lockscrews (11, Figure 6-7) from the lower part of the coupling sleeve (17). Unscrew these lockscrews from the tapped holes in the large flange section of the track sleeve (18).

4. Slide the lower telescope system approximately 1 foot clear of the coupling sleeve (17).

5. Remove the four lockscrews (8) from the upper part of coupling sleeve (17). Unscrew these lockscrews from tapped holes in the lower alignment support section of the second inner tube section lower end coupling (26, Figure 6-6).

6. Unscrew the coupling sleeve (17, Figure 6-7) from the lower part of the second inner tube section lower end coupling threaded periphery (26, Figure 6-6).

6D4. Separation of the lower telescope system. This procedure is performed in the following manner:

1. Remove the two stadimeter collimating screws (13, Figure 4-22) from each half of the lower (split) objective lens and mount assembly. These lockscrews are unscrewed from tapped holes in each mounting plate half (1, Figure 6-7) of the objective operating mechanism assembly. The straight dowel pins (15, Figure 4-22) will be carried out with the mounts (1 and 2) from the mounting plates (1, Figure 6-7).

3. Remove the two taper pins (10) from the two stadimeter transmission shaft thrust collars (4, Figure 6-10) located on the stadimeter transmission shaft (12) on each side of the spider (2) of the first inner tube section assembly.

4. Remove the taper pin (15, Figure 6-7) from the lower part of the stadimeter transmission shaft coupling (3).

5. Slide the stadimeter transmission shaft (12, Figure 6-10) out of the stadimeter transmission shaft coupling (3, Figure 6-7) and clear of the track sleeve (18). Remove this coupling from the operating gear pinion shaft (20).

6. Remove the four lockscrews (9) from the lower part of the track sleeve (18). Unscrew these lockscrews from the tapped holes in the upper alignment support section of the first inner tube section upper end coupling (23, Figure 6-10).

7. Unscrew the track sleeve (18, Figure 6-7) from the upper part of the first inner tube section upper end coupling threaded periphery (23, Figure 6-10), and remove the objective operating mechanism assembly.

8. Remove the stadimeter transmission shaft (12) from the first inner tube section assembly, also removing the two thrust collars (4) from each side of the spider bearing projection (2).

9. Check the reference marks on all four spring loaded packing gland assemblies with corresponding reference marks on the eyepiece box (11, Figure 4-29).

10. Follow the procedure described under Steps 10 to, 22 inclusive of Section 4E5, for the removal of the four spring loaded packing gland assemblies (Figures 4-32, 4-33, and 4-34 respectively), stadimeter transmission shaft spring type packing gland (Figure 4-30), modified hycar type, (Figure 4-31), rayfilter plate (2, Figure 4-40), eyepiece window frame assembly. (Figure 4-38), eyepiece box (11, Figure 4-29), and the eyepiece skeleton assembly (Figure 4-28). All of these assemblies are identical to the Type II periscope.

a. Skeleton head frame. The skeleton head frame (1) is made of cast phosphor-bronze material. It forms the necessary framework to

The skeleton head frame is a sliding fit in the inside bore of the straight 1.99-inch section of the outer taper section.

The prism tilt mechanism is composed of numerous mechanical parts in the upper and

b. Head prism, head prism mount, head prism side plates, and head prism shade. 1. Head prism. The head prism (62) is a right angle prism, made of dense flint optical glass material. It is used to reflect the light rays at right angles. The light rays enter from any position of elevation between 61 degrees elevation to 26 degrees depression in low power and from 49 degrees elevation to 14 degrees depression in high power, and are deflected downward into the instrument from any of the above angles.

2. Head prism mount. The head prism mount (2) carries the head prism (62) with a suitable clamping arrangement. The base pivot shoulder projections of the mount project outward on opposite sides and are a sliding fit in the milled out clearance section in the upper

The rear face of the mount is provided with two bearing projections for the insertion of the extended arm bearing section of the eccentric arm (16) attached to the mount with an eccentric arm pivot pin (56) and secured with a headless lockscrew (46). The skeleton head frame is provided with clearance in its milled out section to receive the eccentric arm (16) and the head prism mount (2) for all degrees of elevation and depression. The head prism (62) is retained from sideward movement with two head prism side plates left and right (4 and 6), and is held to the head prism mount (2) with two pairs of head prism mounting clamps (39 and 40) which are secured with two lockscrews each (47).

3. Head prism side plates. The left and right head prism side plates (4 and 6) are attached to the head prism mount (2) with two lockscrews each (45 and 50). These side plates retain the head prism (62) from sideward movement. Attached to each side plate are two head prism shade wire links (10) secured with rivets (5). The opposite ends of each wire link are secured to each rivet (5) of the head prism shade arms left and right (7 and 8) which are soldered to the head prism shade (9).

Each side plate has a clearance hole to slide over the base pivot shoulder projection of the head prism mount (2) and a bent-over section for its securement to the lower face of the mount with one lockscrew each (45).

4. Head prism shade. The head prism shade (9) is made of sheet brass and is constructed to conform to the contour of the skeleton head periphery. The sides are bent downward and again at 90 degrees to fit into a vertical slot in each of the inner side walls of the skeleton head.

Two arms left and right (7 and 8) are attached to the downward bent sides of the shade by soldering. Each arm is bent and has a protruding

c. Eccentric arm. The eccentric arm (16) is made of phosphor bronze and is 1 7/8 inches in length. The large section has a reamed hole with a stub arm section separated from the long arm section with a sawed slot, and fits over the eccentric disk (17). The stub section is provided with two spacer washers (44) fitted in the slotted section.

The stub arm is provided with two countersunk clearance holes, while the long section of the eccentric arm is provided with coinciding tapped holes for the two lockscrews (43). These lockscrews are inserted in countersunk clearance holes in the stub arm section of the eccentric arm (16) into the clearance holes in the two spacer washers (44) and screwed into tapped holes in the long section of the eccentric arm. The two spacer washers (44) allow sufficient sliding clearance over the eccentric disk (17).

The eccentric arm (16) assembled to the eccentric disk (17) actuates the head prism (62) and its mount (2) by means of the extended arm bearing section assembled over the eccentric arm pivot pin (56) between the two bearing projections of the head prism mount base (2) for elevation and depression.

Two opposite clearance holes are provided in the large section of the eccentric arm for the insertion and removal of the eccentric disk and shaft taper pin (59).

The eccentric warm operates over the eccentric disk (17) and the eccentric disk shaft (18) between the two split bearing projections in the upper part of the skeleton head frame (1).

d. Eccentric disk and shaft. 1. Eccentric disk. The eccentric disk (17) is made of corrosion resisting steel material 1/4 inch in width and 5/8 inch in diameter. It is provided with a reamed hole with its centerline offset from its axis 1/8 inch to accommodate an eccentric disk shaft (18). The eccentric disk is provided with a reamed taper pin hole perpendicular

The offset reamed hole provides the necessary cam movement for the actuation of the head prism mount (2) and its head prism (62) to all the required degrees of elevation and depression.

2. Eccentric disk shaft. The eccentric disk shaft (18) is made of corrosion-resisting steel and is 27/32 inch in length. It is a sliding fit into the reamed holes in the two split bearing projections of the upper part of the skeleton head frame (1) and the offset reamed hole in the eccentric disk (17).

The shaft is secured in the split bearing projections by the tightening of the two lockscrews (41). The two spacer washers (42) fit into the slotted section in each split bearing projection to provide sufficient rotation of the shaft by securing the lockscrews (41). The axial displacement of the shaft is maintained by the eccentric disk (17) and its allowed clearance between the two split bearing projections.

The protruding part of the shaft on the left side carries the head prism shift actuating gear (19) which is secured with a taper pin (58).

e. Head prism shift actuating-gear. The head prism shift actuating gear (19) is made of phosphor bronze material. It has 30 teeth of 60 diametral pitch around its outer circumference, to mesh with the teeth of the fourth intermediate prism shift gear (20).

The reamed hole in the axis of this gear is a push fit on the protruding part of the eccentric disk shaft (18) and is secured with a taper pin (58) through the hub section.

f. Fourth intermediate head prism shift gear and shaft. 1. Fourth intermediate head prism shift gear. The fourth intermediate head prism shift gear (20) is made of phosphor bronze and is 21/64 inch in length. It has 23 teeth of 60 diametral pitch around its outer circumference to mesh with teeth of the third intermediate head prism shift gear (22) on one side, while it meshes with the head prism shift actuating gear (19) on the opposite side. It has two undercut shoulders on opposite ends of 1/64-inch width.

2. Fourth intermediate head prism shift gear shaft. The fourth intermediate head prism shift gear shaft (21) is made of corrosion-resisting steel and is 0.578 inch in length. It is provided with three shoulder sections. The stem section fits into the reamed hole in the skeleton head frame (1) and is secured with a lockscrew (60) located in the front of the skeleton head frame. The medium shoulder is a sliding fit in the reamed hole axis in the fourth intermediate head prism shift gear (20), while the large narrow shoulder serves to retain the above gear axially. The large narrow shoulder has a concave relief to allow clearance for the actuation of the second intermediate head prism shift gear (23).

g. Third intermediate head prism shift gear. The third intermediate head prism shift gear (22) is made of corrosion-resisting steel and is 0.063 inch in width. It is provided with an undercut shoulder of 0.008-inch width for its metal to metal contact upon assembly to the second intermediate prism shift gear (23). It has 14 teeth of 60 diametral pitch around its outer circumference, to mesh with the teeth of the fourth intermediate head prism shift gear (20) as it is fitted into the small countersunk recess in the upper part of the skeleton head left side wall.

This intermediate gear has a reamed hole in its axis which is a sliding fit over the first upper pin projection of the gear train bracket (30). It is provided with two opposite No. 72 drilled holes for the insertion of rivets (61) and is secured to the second intermediate head prism shift gear (23) and riveted.

h. Second intermediate head prism shift gear. The second intermediate head prism shift gear (23) is made of corrosion-resisting steel and is 0.075 inch in width. It is provided with an undercut shoulder of 0.013-inch width. It has 18 teeth of 48 diametral pitch around its outer circumference to mesh with the teeth of the first intermediate head prism shift gear (24) as it is fitted in the countersunk recess in

This intermediate gear has a reamed hole in its axis which is a sliding fit over the first upper pin projection of the gear train bracket (30), with the undercut shoulder fitting in the countersunk recess in the gear train bracket. It is provided with two opposite No. 72 drilled holes for the insertion of rivets (61) and is secured to the third intermediate head prism shift gear (22) and riveted.

i. First intermediate head prism shift gear. The first intermediate head prism shift gear (24) is made of phosphor bronze. It is identical in all other respects to the second intermediate head prism shift gear (23) except that it has no opposite drilled holes for rivets. This intermediate gear has a reamed hole in its axis which is a sliding fit over the second upper pin projection of the gear train bracket (30), with the undercut shoulder fitting in the countersunk recess in the gear train bracket.

It engages with the teeth of the second intermediate head prism shift gear (23) as it is fitted in the countersunk recess in the upper part of the skeleton head left side wall, and with the teeth of the head prism shift gear (25) on its lower opposite side.

j. Head prism shift, gear and shifting racks. 1. Head prism shift gear. The head prism shift gear (25) is made of corrosion-resisting steel and is 0.075 inch in width. It is provided with an undercut shoulder of 0.013-inch width. It has 23 teeth of 48 diametral, pitch around its outer circumference to mesh with the teeth of the head prism shifting racks right and left (14 and 15), and the first intermediate head prism shift gear (24) as it is fitted in the countersunk recess in the upper part of the skeleton head left side wall.

It is provided with a reamed hole in its axis which is a sliding fit over the second lower pin projection of the gear train bracket (30) with the undercut shoulder fitting in the countersunk recess of the gear train bracket.

2. Head prism shifting racks. The right and left head prism shifting racks (14 and 15) are made of blued cold rolled steel, and operate

The shifting wire tape (38, Figure 4-28), overlaps the narrow flat shoulder in the lower part of the skeleton head and is attached to the shifting rack (15) which is slightly higher. The clamp block (11) is made of the same material as the shifting rack and coincides with the length and width of the offset and main section. The periphery of the clamp block conforms to the contour of the skeleton head, as it operates vertically with the shifting rack slightly below the skeleton head periphery.

Above the offset section of the shifting rack, a protruding integral stop section 11/32 inch in length is located approximately 21/32 inch from the lower end. Its outer surface is provided with a radius slightly below the contour of the skeleton head periphery. The stop section in contact with the lower side of the cube bracket (27) restricts the movement of the head prism (62) in the elevated position to its designed limits, thus preventing any damage to the head prism (62) and its operating mechanism.

The right head prism shifting rack (14) is similar to the left in design, except that it is constructed to the opposite hand. Its teeth mesh with the teeth of the head prism shift gear (25) on the right side. The integral stop section of this shifting rack when in contact with the lower side of the cube bracket (27) restricts the movement of the head prism (62) in the depressed position to its designed limit.

k. Gear train bracket. The gear train bracket (30) is made of blued cold rolled steel,

The lower integral pin projection serves as a pivot for the reamed axis hole in the Galilean eyepiece lens cube (35). The second upper pin projection is of sufficient length to protrude into the reamed axis hole in the head prism mount (2) base pivot shoulder projection serving as a pivot for the left side of the mount. All four pin projections are a sliding fit into the reamed holes in the left side wall of the skeleton head. The bracket is secured in the flat recess face of the skeleton head left side wall with four lockscrews (54) located in the lower part. The periphery of the bracket when assembled to the skeleton head conforms to the skeleton head periphery.

l. Cube bracket. The cube bracket (27) is made of blued cold rolled steel. It serves to retain the lower part of the head prism shifting racks right and left (14 and 15). The pin projection integral with the cube bracket serves as a pivot for the reamed hole axis of the Galilean objective lens cube (34).

The pin projection is a sliding fit into the reamed hole in the skeleton head vertical centerline of the left side wall. The bracket is secured to the flat recess face of the skeleton head with two lockscrews (53) which are inserted in countersunk clearance holes in the bracket on opposite sides of the pin projection and screwed into tapped holes in the skeleton head. This bracket serves as a stop for each integral stop section of the head prism shifting racks (14 and 15) for the elevation and depression positions of the head prism (62).

m. Galilean eyepiece lens, lens mount housing, lens cube, objective lens, and objective lens cube. The Galilean telescope system is composed of two lenses; namely, a

1. Galilean eyepiece lens. The Galilean eyepiece lens (63) is made of two optical elements. It consists of a divergent meniscus flint element, cemented to the equi-concave crown element, forming a negative doublet. The divergent meniscus element cemented to the equi-concave element of the Galilean eyepiece lens corrects for spherical and chromatic aberration. It is mounted in the Galilean eyepiece lens mount (36) and burnished in place. The threaded periphery of the mount can be screwed vertically in the threads of the Galilean eyepiece lens mount housing (37) by using a sharp pointed scribe inserted in any one of a series of eight drilled recesses. This vertical movement provides a means for focusing the Galilean eyepiece lens for elimination of parallax in low power.

2. Galilean eyepiece lens mount housing. The Galilean eyepiece lens mount housing (37) is provided with an internal threaded bore to carry the threaded periphery of the mounted Galilean eyepiece lens (63) and mount (36) vertically. Two undercut shoulders, one on each side of the flange section, provide sufficient body distance for the movement of the mounted Galilean eyepiece lens (63) and mount (36) to eliminate parallax. The housing flange has three equally spaced clearance holes. One hole is a pivot hole, while the other two are elongated for collimation. A tapped hole located in the undercut shoulder receives the lockscrew (52) used to secure the mounted Galilean eyepiece lens (63) and mount (36) after parallax removal.

3. Galilean eyepiece lens cube. The Galilean eyepiece lens cube (35) is constructed of a suitable blued cold rolled steel framework for holding the Galilean eyepiece lens mount housing (37). By means of integral pin projections of the cube bracket (27) and the gear train bracket (30) extending in the reamed hole axis in opposite sides of the cube, it can be rotated for change of power. The undercut shoulder 0.010 inch in width and 0.437 inch in diameter on each side face provides sufficient bearing wall for preservation of alignment between the inner walls of the skeleton head. All corners are

The clearance hole in the upper face of the cube allows the lower undercut shoulder of the Galilean eyepiece lens mount housing (37) sufficient free movement for collimation of the Galilean eyepiece lens (63). Three equally spaced tapped holes in the upper face, receive lockscrews (38) to secure the Galilean eyepiece lens mount housing (37) after collimation. The lower wall is bored and provided with antireflection threads. The front and rear walls are also bored and have antireflection threads, thus offering no obstruction for the entering light rays in either high or low power. The skeleton head is machined out, leaving only the side walls, center support, and lower section for the assembly, disassembly, and actuation of this cube.

4. Galilean, objective lens. The Galilean objective lens (64) is made of two optical elements. It consists of a double convex flint element cemented to a divergent meniscus dense crown element forming a positive objective lens doublet. It is mounted in the Galilean objective lens cube (34) and secured with a Galilean objective lens retainer (3). The retainer is spot soldered to the Galilean objective lens cube (34) to prevent it from unscrewing.

5. Galilean objective lens cube. The Galilean objective lens cube (34) is constructed similarly to the Galilean eyepiece lens cube (35). The lower part is counterbored a shallow depth to serve as a mount for the Galilean objective lens (64), while its outer shoulder is threaded to receive the internal threaded section of the Galilean objective lens retainer (3). The upper, front, and rear walls are bored and provided with antireflection threads, thus offering no obstruction for the entering light rays in either high or low power. The two perpendicular 90 degrees

The change of power mechanism is located on the right side wall of the skeleton head frame (1) and is composed of numerous parts to operate the Galilean telescope system.

n. Cube shifting racks. The cube shifting racks right and left (12 and 13) operate in vertical slots located in the right side wall of the skeleton head. These shifting racks are made of blued cold rolled steel and are constructed similarly to the head prism shifting racks right and left (14 and 15). The right cube shifting rack (12) is wider, and is provided with two assembled and riveted pins (65). These pins extend through two elongated holes in the wide vertical slot to the right of the vertical centerline and into the elongated holes in the Galilean eyepiece lens and objective lens cubes (35 and 34).

These pin projections (65), by the movement of the right or left cube shifting racks (12 and 13), shift the Galilean telescope system to the IN or OUT position. That is, each cube carrying one lens doublet each of the Galilean telescope is shifted simultaneously to place the lenses in the line of sight for low power, or out of the line of sight to allow the light rays free passage through the cubes for high power.

The cubes (34 and 35) are retained in either position by means of two pawls (32) extending through elongated slots under spring tension in either 90 degrees V-groove in the right side wall of each cube. The right and left cube shifting racks (12 and 13) are provided with 10 teeth of 48 diametral pitch located 2 7/32 inches from the lower end in a distance of 11/16 inch, to engage the power shift gear (26) on opposite sides.

This left cube shifting rack (13) operates in the vertical slot to the left of the vertical centerline. When it is pulled downward by the shifting wire tape (38, Figure 4-28), its teeth in mesh with the power shift gear (26) cause it to rotate. The power shift gear is also in mesh with the teeth of the right cube shifting rack (12) and causes it to be carried upward. By means of the protruding pins (65) extending through the elongated holes in the skeleton head and into the elongated holes in each cube, the power shift gear rotates the cubes to the OUT position and vice versa.

The integral stops of the cube shifting racks projecting outward in each vertical recess groove, contact the lower side face of the lower cube bracket (27) to restrict the movement of each cube beyond its 90 degrees V-groove engagement of both pawls (32).

The lower section of the skeleton head is provided with a flat shallow groove in the right side in similar manner to the left side. The lower part of each cube shifting rack is offset in similar manner to the head prism shifting racks (14 and 15) for the attachment of the shifting wire tape (38, Figure 4-28), clamp blocks (11) and lockscrews (49).

o. Power shift gear and pawls. 1. Power shift gear. The power shift gear (26) is made of corrosion-resisting steel, and is provided with two undercut shoulder sections 0.005 inch wide on opposite sides. It has 12 teeth of 48 diametral pitch around sits outer circumference. The gear sets in a countersunk recess in the vertical centerline and central part in the right side wall of the skeleton head (1). Its gear teeth are in mesh with the teeth of both cube shifting racks right and left (12 and 13) on opposite sides. A reamed hole in the renter axis of the gear is a sliding fit over the pin projection of the power shift gear bracket (29), with its outer shoulder fitting in the countersunk recess in this bracket. This gear serves to provide movement to the opposite cube shifting rack, carrying it upward as one cube shifting rack is carried downward and vice versa.

Each pawl is attached to a pawl holder (31) made of sheet bronze and having two rivets (57). The left vertical slot of the skeleton head frame has three enlarged recess sections to accommodate the wider sections of the pawl holders (31) and the reinforcing spring (33). The pawl holders and the reinforcing spring are secured with two lockscrews each (48). The reinforcing spring (33) is made of clock spring material, bent to shape, with a wide center section for the insertion of two lockscrews (48). The upper and lower narrow sections of the reinforcing spring (33) overlapping the ends of the power shift pawls (32), provide a sufficient spring tension to retain the detent in the 90 degrees V-grooves for either the IN or OUT position of the cubes.

p. Cube brackets. The two cube brackets (27) are made of blued cold rolled steel material with pin projections integral with the bracket. The pin projection of the upper bracket is a sliding fit in the reamed hole in the vertical centerline of the skeleton head, and it extends into the reamed hole axis in the Galilean eyepiece, lens cube right side (35) to serve as a pivot. The bracket is secured in the flat milled recess over the upper part of the cube shifting racks right and left (12 and 13) with two lockscrews (53). These lockscrews are inserted in countersunk clearance holes in the bracket on opposite sides of the pin projection and screwed in tapped holes in the right side wall of the skeleton head.

The lower cube bracket serves the same purpose as noted for the Galilean eyepiece lens cube (3S) except that it is used for the Galilean objective lens cube (34). The lower side of this cube bracket serves as a stop for the integral stop sections of the cube shifting racks right and left (12 and 13) as they contact it alternately for the IN and OUT positions of the cubes.

r. Head prism base bracket. The prism base bracket right (28) is constructed similarly to the cube brackets (27). It is provided with a pin projection integral with the bracket, which serves as a pivot for the reamed axis hole in the base pivot shoulder projection of the head prism mount (2). The pin projection is a sliding fit in the reamed hole in the vertical centerline of the upper part of the skeleton head right side wall, and is secured with two lockscrews (51).

6E2. Disassembly of the skeleton head assembly. The skeleton head assembly is disassembled as follows:

1. Move the cube shifting racks right and left (12 and 13), shifting the Galilean telescope system to the OUT position. This allows the Galilean objective lens (64), lens retainer (3), eyepiece lens (63), lens mount (36), and lens mount housing (37) to be removed in the following manner.

2. Remove the three lockscrews (38) from the flange of the Galilean eyepiece lens mount housing (37). These lockscrews are unscrewed from the tapped holes in the eyepiece lens cube (35). Remove the lens mount housing (37) with the mounted eyepiece lens (63) and its mount (36). Remove the lockscrew (52), unscrewing it from the housing (37) and unscrew the mounted eyepiece lens (63) and its mount (36) from the housing (37). Wrap the mounted Galilean eyepiece lens in clean lens tissue and store it in a box to prevent scratches and breakage.

3. Scrape off the spot solder from the Galilean objective lens retainer (3) and cube

4. Remove the four lockscrews (54) from the gear train bracket (30). These lockscrews are unscrewed from tapped holes in the left side wall of the skeleton head (1). Careful attention and skill are required to remove the gear train bracket. Since the gear train bracket (30) has four pin projections, it must be lifted evenly. Remove the gear train bracket observing these precautions.

5. Remove the head prism shift gear (25).

6. Remove the first intermediate head prism shift gear (24).

7. Remove the second and third intermediate head prism shift gears (23 and 22).

8. Remove the lockscrew (60) from the lower part of the upper front wall right side, unscrewing it from its contact with the fourth intermediate head prism shift gear shaft (21).

9. Insert a 2-64 tap or special screw in the large shoulder axis tapped hole in the fourth intermediate head prism shift gear shaft (21) and pull the shaft with the fourth intermediate head prism shift gear (20) clear of the skeleton head, removing the gear from the shaft.

10. Remove the two lockscrews (53) from the cube bracket (27) on the left side of the skeleton head (1). These lockscrews are unscrewed from the tapped holes in the left side wall of the skeleton head (1). Remove the cube bracket (27), raising it carefully in order not to break its integral pin projection.

11. Remove the head prism shifting racks right and left (14 and 15), carrying with them the assembled clamp blocks (11) and lockscrews (49).

12. Remove the two lockscrews (53) from each of the two cube brackets (27) on the right side of the skeleton head. These lockscrews are unscrewed from the tapped holes in the skeleton head right side wall. Remove both cube brackets (27), raising each one carefully in order not to break the integral pin projections of each cube bracket.

14. Remove the cube shifting racks right and left (12 and 13), carrying with them the assembled clamp blocks (11) and lockscrews (49).

15. Remove the power shift gear (26).

16. Remove the Galilean objective lens and eyepiece lens cubes (34 and 35) sliding them out from the center and front of each opening in the skeleton head (1).

17. Remove the two lockscrews (48) from the reinforcing spring (33), unscrewing these lockscrews from tapped holes in the center enlarged recess in the outer left vertical slot in the skeleton head right side wall. Remove the reinforcing spring (33).

18. Remove the two lockscrews (48) from each upper and lower pawl holder (31) and remove the pawl holders and pawls (31 and 32). All lockscrews (48) for pawl holders and pawls are unscrewed from tapped holes in the enlarged recesses in the outer left vertical slot in the skeleton head right side wall.

19. Remove the two lockscrews (51) from the head prism base bracket (28). These lockscrews are unscrewed from tapped holes in the upper part of the skeleton head right side wall. Remove the head prism base bracket (28), raising it carefully in order not to break its integral pin projection.

20. Press one side of the head prism shade (9) inward to snap it out of the vertical slot of the skeleton head inner side walls.

21. Push the mounted head prism (62) out from the front of the skeleton head, swinging it with the eccentric arm (16) completely around to the rear, resting the eccentric arm on the skeleton head upper wall.

22. Remove the lockscrew (46) from the left bearing projection of the head prism mount (2). This lockscrew is unscrewed from its contact with the eccentric arm pivot pin (56). Push the eccentric pivot pin outward from the

23. Remove the two lockscrews (45) from the bent over section of each head prism side plate (4 and 6). These lockscrews are unscrewed from tapped holes in the head prism mount base (2). Remove the lockscrew (50) from each head prism side plate (4 and 6), removing the two head prism side plates, and carrying the head prism shade (9) and its wire links (10) with them. The two lockscrews (50) are unscrewed from tapped holes in opposite sides of the head prism mount (2).

24. Remove the two lockscrews (47) from each of the upper two head prism mounting clamps (39 and 40). These lockscrews are unscrewed from tapped holes in the upper opposite side beveled faces of the head prism mount (2). Remove the two head prism mounting clamps (39 and 40).

25. Slide the head prism (62) upward and out of the remaining two lower head prism mounting clamps (39 and 40), removing the head prism (62). The lower two head prism mounting clamps (39 and 40) remain in place for reassembly. Wrap the head prism in clean lens tissue and store it in a box to prevent scratches and breakage.

26. Rotate the head prism shift actuating gear (19) carrying with it the eccentric disk shaft (18) and eccentric disk (17) and look for the small end of the taper pin (59) through the clearance hole in the large section of the eccentric arm (16). When the small end of the taper pin (59) is lined up with the opposite clearance holes in the eccentric arm, use a small drift punch to remove the taper pin.

27. Remove the lockscrews (41) located in each split bearing projection of the skeleton head upper part. These lockscrews are unscrewed from tapped holes in the lower part of each skeleton head split bearing projection. Remove the two spacer washers (42) from the split sections of the bearing projections, and place them with proper reference marks in a special envelope to separate them for reassembly.

29. Remove the eccentric disk (17), sliding it out of the large section of the eccentric arm. Remove the two lockscrews (43), unscrewing them from the tapped holes in the long arm section of the eccentric arm (16). Remove the two spacer washers (44) from the split section of the stub arm section of the eccentric arm (16). Mark each spacer washer (44) with proper identification marks for replacement.

30. Place the hub section of the head prism shift actuating gear (19) on a brass V-block for the removal of the taper pin (58). It requires an additional helper to drift out the taper pin (58). Remove the head prism shift actuating gear (19) from the eccentric disk shaft (18) after the removal of the taper pin (58).

6E3. Reassembly of the skeleton head assembly. The skeleton head assembly is reassembled as follows:

1. Apply Lubriplate No. 110 lightly to all rotating parts as the reassembly procedure is followed.

2. Place the head prism shift actuating gear (19) on the eccentric disk shaft (18) and secure it with a taper pin (58). The hub section of the gear faces outward.

3. Place the two spacer washers (44) in the slotted section of the eccentric arm (16), replacing them in their proper position as noted by the reference marks made upon disassembly. Insert the two lockscrews (43), screwing them down snugly to a temporary setting.

4. Place the eccentric disk (17) in the large section of the eccentric arm (16). A reference scribed line on the left side of the eccentric disk (17) and the eccentric arm (16) designates their proper assembly.

5. Place a special taper pin in the clearance hole of the eccentric arm large section (16)

6. Place the eccentric arm (16) with the assembled eccentric disk (17) in the section between the two split bearing projections in the upper part of the skeleton head (1). Place the eccentric disk shaft (18) with the larger section of the taper pin hole facing toward the inserted special taper pin of the eccentric arm (16) and disk (17). Place the shaft in the left split bearing projection reamed hole in the skeleton head, carrying it through the eccentric disk (17) and further into the reamed hole in the opposite split bearing projection.

7. Remove the inserted special taper pin, and insert a drift punch through the clearance hole in the eccentric arm (16) and the taper pin holes in the eccentric disk (17) and shaft (18) for proper alignment of the taper pin holes. Remove the drift punch and insert the taper pin (59), securing it tightly with the use of a drift punch and small ball peen hammer.

8. Place the spacer washers (42) in the slotted section of each split bearing projection and insert the two lockscrews (41). These lockscrews are inserted into clearance holes in each upper split bearing cap into the spacer washer clearance holes and screwed into the lower split bearing projection tapped holes. Secure each lockscrew tightly, and check the rotation of the eccentric disk shaft (18). It may be necessary to finish off each spacer washer (42) to eliminate any excessive looseness of the shaft in the split bearings, for further tightening of the caps.

9. Check the movement of the eccentric disk (17) in the eccentric arm (16). It should have free movement without looseness. This is accomplished by removing the spacer washers (44) and finishing them off lightly on a fine abrasive stone, to permit further tightening of the eccentric arm stub arm section.

10. Assemble the left and right head prism side plates (4 and 6) to opposite sides of the head prism mount (2). Secure each side plate with two lockscrews (50). These lockscrews extend into tapped holes in the opposite sides of the head prism mount. Insert two lockscrews

11. Clean the head prism (62) using clean lens tissue; also clean off any surface dust. Place the head prism with its hypotenuse face on the scraped head prism mount (2), sliding the lower 90 degree face under the 60 degree prongs of the two assembled head prism mounting clamps (39 and 40). Apply the upper two head prism mounting clamps (39 and 40) to the upper beveled side faces of the head prism mount (2), securing each with two lockscrews (47). Take precautions to note that the 60 degree prongs of the clamps touch the 90 degree faces of the head prism (62).

12. Swing the extended arm bearing of the eccentric arm (16) to the rear of the skeleton head. Place the bearing projections of the head prism mount (2) over the extended arm bearing section, and insert the eccentric arm pivot pin (56) through the reamed hole in the bearing projection and the reamed hole in the extended arm bearing section of the eccentric arm (16). Carry the eccentric arm pivot pin in the opposite bearing projection of the head prism-mount (2). Secure the pivot pin (56) with a lockscrew (46) which extends into the left rear bearing projection tapped hole of the head prism mount base (2) and contacts the spotted recess in the eccentric arm pivot pin (56).

13. Swing the mounted head prism (62) and mount (2), carrying with it the eccentric arm (16), into the front clearance section of the skeleton head. Carry it in until the pin projection reamed holes of the skeleton head left and right side walls and the head prism mount side base pivot projections are in coincidence. Insert the pin projection of the head prism base bracket (28) in the reamed hole in the skeleton head sight side wall and farther into the reamed hole in the head prism mount side base pivot projection. Check the stamped reference numerals on the bracket and skeleton head for correct reassembly. Secure the bracket with two lockscrews (51). These lockscrews extend into

14. Rotate the head prism shift actuating gear (19) counterclockwise, placing the head prism (62) at the extreme limit of depression. Place the fourth intermediate head prism shift gear (20) on its shaft (21). Observe the position of the spotted recess in the stub section of the shaft for proper alignment with the tapped hole in the front lower part of the split bearing projection. Carry the fourth intermediate head prism shift gear shaft (21) with the gear (20) in the semicircular clearance provision of the skeleton head left side wall; the stub section of the shaft is carried into the reamed hole below the split bearing projection. Slide the teeth of the fourth intermediate head prism shift gear (20) into engagement with the head prism shift actuating gear teeth (19). Push the stub section of the shaft in until the medium shoulder of the shaft is in contact with the countersunk semicircular clearance provision face. Insert the lockscrew (60) in the tapped hole below the split bearing projection, screwing the lockscrew into the spotted recess in the fourth intermediate head prism shift gear shaft stub section (21) for its securement.

15. Place one side of the head prism shade (9) in the vertical slot in the skeleton head inner right side wall, and snap the opposite side of the shade into the vertical slot in the skeleton head inner left side wall.

16. Place the Galilean objective lens and eyepiece lens cubes (34 and 35) in their respective openings in the skeleton head (1). Check the cubes to ascertain that they are located for the IN position.

17. Place the pawl holders (31) and the assembled pawls (32) in the outer vertical slot in the right side wall of the skeleton head. The pawls fit in the elongated slots, and the pawl holders in the enlarged recesses in the upper and lower part of this vertical slot. Secure each pawl holder (31) with two lockscrews (48). These lockscrews extend into tapped holes in the enlarged recess slot.

18. With the Galilean objective lens and eyepiece lens cubes (34 and 35) located in the IN position, apply the right cube shifting rack

19. Place the left cube shifting rack (13) in the center of the three vertical slots in the skeleton head right side wall.

20. Reassemble the two cube brackets (27) to the flat grooves in the right side wall of the skeleton head over the cube shifting racks right and left (12 and 13). Place the pin projection of each cube bracket in the reamed holes in the skeleton head and the reamed axis hole in each cube. Carefully push the pin projection of the cube bracket down into the reamed axis hole in each cube. Secure each cube bracket with two lockscrews (53). These lockscrews extend into tapped holes in the right side wall of the skeleton head.

21. Place both head prism shifting racks right and left (14 and 15) in the vertical slots in the skeleton head left side wall. The clamp blocks (11) and lockscrews (49) remain assembled to the head prism shifting racks.

22. Reassemble the cube bracket (27) to the flat groove in the left side wall of the skeleton head over the head prism shifting racks right and left (14 and 15). Place the pin projection of the cube bracket in the reamed hole in the skeleton head and reamed hole axis in the Galilean objective lens cube (34). Carefully push the pin projection of the cube bracket down into the reamed hole axis in the cube. Secure the bracket with two lockscrews (53) which extend into tapped holes in the groove seat.

23. To align the gear train for the head prism shift mechanism, check the scribed line of the eccentric disk (17) and the eccentric arm (16) large section for coincidence. This position places the head prism (62) in the full elevated position. In this position move the left head prism shifting rack (15) upward until its stop is in contact with the lower side face of the cube bracket (27). Move the right head prism shifting rack (14) downward and measure a distance of 0.625 inch from the lower side face of the cube bracket (27) to the upper shoulder of the integral stop of the head prism shifting rack. This distance is required to shift the head prism (62) to 45 degrees elevation and 10 degrees depression.

25. Place the first intermediate head prism shift gear (24) so that its reference line coincides with the reference line of the head prism shift gear (25) for proper engagement in the countersunk recess in the skeleton head left side wall.

26. Place the second and third intermediate head prism shift gears together in the small and large countersunk recesses in the left side wall of the skeleton head. Check the reference line of the second intermediate head prism shift gear (23) for proper engagement by lining it up with the corresponding reference line of the first intermediate head prism shift gear (24). The third intermediate head prism shift gear (22) assembled to the second gear (23) engages with the teeth of the fourth gear (20) when the alignment stated in Step 23 is maintained.

27. Ascertain that all bearing holes of this gear train align with the reamed holes in the skeleton head left side wall. Carefully place the pin projections of the gear train bracket (30) in the center bearing holes in the gear train and press downward slowly. The second upper pin projection will enter first. It extends into the first intermediate head prism shift gear (24), and farther into the skeleton head left side wall and reamed hole axis in the pivot shoulder projection of the head prism mount (2). The lower pin projection extends into the skeleton head left side wall and into the reamed hole axis in the Galilean eyepiece lens cube (35). Secure the gear train bracket with four lockscrews (54) which extend into tapped holes in the skeleton head left side wall.

28. With the use of a surface gage and dial indicator attachment, stand the skeleton head

Follow the same procedure for the Galilean objective lens cube (34) using the lower face of the cube for determining the true horizontal measurement. Release the two lockscrews (48) and move the lower pawl holder (31) and pawl (32) axially to obtain a true horizontal measurement. This measurement determination of the Galilean telescope mechanism in a true horizontal position is made so that upon the assembly of the lenses, the optical line of sight of this system will be parallel to the optical line of sight of the remaining telescope systems. This prevents a pronounced general aberration which results when the IN position pawl holders (31) and pawls (32) have a faulty alignment.

29. With the Galilean objective lens and eyepiece lens cubes (34 and 35) located in the IN position, place the left cube shifting rack (13) with its integral stop against the lower side face of the lower cube bracket (27). In this position, insert the power shift gear (26) to coincide its reference mark with the mating reference mark of the right cube shifting rack (12) in the countersunk recess in the skeleton head right side wall. The teeth of the gear in the countersunk recess mesh with the teeth in the right and left cube shifting racks (12 and 13) on opposite sides. The clamp blocks) (11) and lockscrews (49) remain assembled to the cube shifting racks.

30. Reassemble the power shift gear bracket (29) to the flat, groove in the right side wall of the skeleton head over the cube shifting racks right and left (12 and 13). Carefully: push the pin projection of the bracket into the reamed

31. Check the movement of the Galilean objective lens and eyepiece lens cubes (34 and 35) in the IN and OUT positions to ensure that a positive engagement of the pawls in the 90 degrees V-grooves in the cubes is obtained.

32. Shift the Galilean objective lens and eyepiece lens cubes (34 and 35) to the OUT position.

33. Clean the Galilean eyepiece lens (63), using clean lens tissue; also clean off the surface dust.

34. Reassemble the mounted Galilean eyepiece lens (63) and mount (36) in the lens mount housing (37). Attach the housing to the lens cube (35), placing the pivot hole downward, and securing it with three lockscrews (38). These lockscrews extend into tapped holes in the face of the cube. Collimation of this lens doublet will be accomplished in the collimation of the instrument.

35. Clean the Galilean objective lens (64), using clean lens tissue; also clean off any surface dust. Place this lens doublet in the objective lens cube (34), with the flint element resting in the counterbored seat in the cube and replace the retainer ring (3), clamping the lens doublet. Spot solder the retainer ring to the cube to prevent its backing off the threaded periphery of the cube.

36. Shift the head prism (62) to the zero line of sight by eyesight, and shift the Galilean telescope system to the IN position. Wrap the skeleton head assembly in clean lens tissue and store conveniently to preserve it from damage, until the assembly is required for collimation.