SHEARS

Shears, made by lashing two legs together with a rope, is well adapted for lifting heavy machinery or other bulky loads. It is formed by two members crossed at their tops with the hoisting tackle suspended from the intersection. The shears must be guyed to hold it in position. The shears is quickly assembled and erected. It requires only two guys and is adapted to working at an inclination from the vertical. The shear legs can be round poles, timbers, heavy planks, or steel bars, depending on the material at hand and the purpose of the shears. For determining the size of the members to be used, the load to be lifted and the ratio of the length and diameter of the legs are the determining factors. For heavy loads the length-diameter (L/ d) ratio should not exceed 60, because of the tendency of the legs to bend, rather than to act as columns. For light work, shears can be improvised from two planks or light poles bolted together and reinforced by a small lashing at the intersection of the legs.

1. Rigging. In erection, the spread of the legs should equal about one half of the height of the shears. The maximum allowable drift (inclination) is 45 degrees. Tackle blocks and guys for shears are essential. The guy ropes can be secured to firm posts or trees with a turn of the rope so that the length of the guys can be adjusted easily. The procedure is as follows:

a. Lay two timbers together on the ground in line with the guys with the butt ends pointing toward the back guy and close to the point of erection.

b. Place a large block under the tops of the legs just below the point of lashing (fig. 6-56), and insert a small spacer block between the tops at the same point. The separation between the legs at this point should be equal to one third of the diameter on one leg to make handling of the lashing easier.

c. With sufficient 1-inch rope for 14 turns around both legs, make a clove hitch around one mast, and take 8 turns around both legs above the clove hitch. Wrap the turns tightly so that the lashings are made smooth and without kinks.

d. Finish the lashing by taking two frapping turns around the lashing between the legs and securing the end of the rope to the other leg just below the lashing. For handling heavy loads the number of lashing turns is increased.

2. Erecting. Holes should be dug at the points where the legs of the shears are to stand. In case of placement on rocky ground, the base for the shears should be level. The legs of the shears should be crossed and the butts placed at the edges of the holes. With a short length of rope, make two turns over the cross at the top of the shears and tie the rope together to form a sling. Be sure to have the sling bearing against the masts and not on the shears lashing entirely. The procedures is as follows:

a. Reeve a set of blocks and place the hook of the upper block through the sling. Secure the sling in the hook by mousing. Fasten the lower block to one of the legs near the butt, so it will be in a convenient

Figure 6-56.-Lashing for shears.

position when the shears have been raised, but will be out of the way during erection.

b. If the shears are to be used on heavy lifts, another tackle is rigged in the base guy near its anchorage. The two guys should be secured to the top of the shears with clove hitches to legs opposite their anchorages above the lashing.

c. Several men (depending on the size of the shears) should lift the top end of the shear legs and "walk" them up by hand until the tackle on the rear guy line can take affect. After this, the shear legs can be raised into final position by hauling in on the tackle. Secure the front guy line to its anchorage before raising the shear legs and keep a slight tension on this line to control movement. (See fig. 6-57.)

d. The legs should be kept from spreading by connecting them with rope chain, or bards. It can be necessary, under some conditions, to anchor each leg of the shears during erection to keep the legs from sliding in the wrong direction.

3. Operating. The rear guy is a very important part of the shears rigging, as it is under a considerable strain when hoisting. The front guy has very little strain on it and is used mainly to aid in adjusting the drift and to steady the top of the shears when hoisting or placing the load. It maybe necessary to rig a tackle in the rear guy for handling heavy loads. In operation, the drift (inclination of the shears) desired is set by adjustment of the rear guy, but this should not be done while a load is on the shears. For handling light loads, the fall line of the tackle of the shears can be led straight out of the upper block. When heavy loads are handled, you should lash a snatch block (fig. 6-58) near the base of one of the shear legs to act as a leading block, The fall line should be run through the leading block to a hand- or power-operated winch for heavy loads.

Figure 6-57.-Erecting shears

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