Mm Mortar

part S by Clyde Barrow

I_ Introduction

This final segment of the 60mm Mortar series will cover the following areas: Section II Completion of the bipod and collar assemblies. Section III M~4 Mortar sight.

If you intend to build a 60mm Mortar you should obtain a copy of the Ariny manual which contains complete info on setup, aiming, firing and maintenance.

US Army FM 23-85, 60mm Mortar. $5ppd. Available from: Arm & Merchant Books, 1210 J Street, Modesto, CA 95354.

This firm also carries firing tables, plotting charts and similar data related to the 60mm Mortar. Contact them for more info and prices.

Please note the two corrections marked in Figure One. The area shown is from the right side of the section on building the yoke/ PMA Vol.2 page 111. Ed.

Figure Two

Figure One

II Completion of Bipod and Collar Assemblies.

I.-Saddle- Collar Latch (See Fig.2)

a. After hinging the two collar halves as outlined in Issue 3, weld one .75"xl.O" slotted tab to each half of the collar.

b. Weld two hinge tubes to the bottom edge of the lower tab.

c. Weld a third hinge tube to the bottom of the clamp bolt.

d. Assemble hinged bolt to the lower collar assembly.

e. Construct and install the "tall" nut as shown in Fig. 2.

Tall Nut

O Tuka

Tall Nut

Clamp Bolt-

Upper Tab

O Tuka

Upper Tab

21535 Fiber Thrust Washer
Upper Collar

¿.-Elevation Mechanism (Cont. from PMA Vol.

-Individual Parts Specs (See Fig.3)

a. Elevation Tube: 1.0"0D - .065 wall X 12" long (see Vol.2 pg.118).

b. Guide Tube: 1.25"0D - .065 wall X 11.5" long (see Vol.2 pg.118).

c. Elevation Screw: 5/8" threaded rod (5/8 NC X 11 TPI) X 12" long. Weld a 5/8" nut in place on the screw with 2" of thread exposed beyond the nut.

d. Thrust Washers (2): .65"ID/1.0"0D. Washers may be fiber or nylon, approximately .1" thick.

e. Elevation Crank: 5/8 NC threads. You may modify an existing crank or build one from scratch as shown in Fig.3. Crank can be secured with a set screw,pin or jam nut.

-Final Assembly (Fig.4)

a. Turn elevation screw into the lower end of ¿he elevation tube.

b. Drop thrust washer into the guide tube. It should come to rest on the top of shoulder welded into the tube's bottom.

c. Align guide strip on elevation tube w/guide slot in the top bushing of the guide tube. Slide elevation tube down into the guide tube until it rests on the thrust washer.

d. Install a second thrust washer and the elevation crank on the screw protruding from the bottom of the guide tube.

e. Elevation tube should move up and down freely when crank is turned. Be sure to apply grease to all surfaces before assembly.

60mm Mortar Schematic
12.25" ELEVATION TUBE

_3.-Transverse Mechanism (See Fig.5) -Individual Parts Specs a. Transverse Screw: 5/8" threaded rod

Weld a 5/8" NC nut in place on the screw with 8.5" of thread exposed. File a groove for shaft collar installation.Groove location is determined after test fitting the screw in the yoke assembly.

b. Handwheel: 5/8"NC threads.

Modify an existing handwheel or build one from scratch as shown in Fig.5.(Folding handle is optional).

c. Sleeve: 5/8"ID metal tube.

Cut to length to fit over screw between the yoke and handwheel assemblies. (Non-functional/serves as a thread cover only.)

d. Transverse Screw Retainer:

Use a commercial 5/8"ID shaft collar. Collar is secured in place w/set screw that fits into a groove cut in the transverse screw.

e. Thrust Washer (2): Same as used in

Elevation Screw Assembly. (II2d)

-Final Assembly (See Fig.6)

a. Slip one thrust washer over the end of the transverse screw.

b. Insert screw through the bushing in the right leg of the yoke assembly.

c. Slip on a second thrust washer followed by the shaft collar.

d. Turn the screw into the nut on the elevation tube. Continue to turn until the tube is about centered on the screw.

e. Feed the screw into the bushing on the left leg of the yoke assembly.Continue until the outer thrust washer is flush against the outside of the yoke assembly.

f. Slide the collar into position and mark the screw for cutting the groove.When groove is cut, secure the collar in place.

Additional washers may be used to take up any side play in the finished assembly.

g. Install sleeve and handwheel on outside of screw assembly.

h. Transverse nut should move freely on screw when wheel is turned.

Coarse/Fine Leveling Adjustments Fig.7

a. Leg Clamp (Coarse Adjustment). Construct clamp from a block of aluminum as outlined in Fig.7. Finished clamp should hold firmly when tightened and should slide freely when loosened. Secure clamp to bipod leg w/same screw and "tall" nut shown in Fig.2.

b. Turnbuckle (Fine Adjustment) Fig.8 Use any conmercial turnbuckle that measures about 3.5" closed and 5" when extended. Secure one end to the leg clamp and the other to the tabs on the elevation tube.

c. Turnbuckle Mount Tabs Fig.9 Cut two .75" square tabs from 12

gage steel sheet. Drill one mount hole through the center of each tab. The outer edges of the tabs can be ground to a .375" radius if desired. Weld the tabs to the elevation tube with the mount holes about 1.5" from the tube bottom. The space between the tabs should be sufficient to allow insertion of the turnbuckle eye plus two washers.

Bipod Leg

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    How to build 60mm mortar?
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