LADDER DITCHER

The boom on the ladder ditcher (fig. 9-67) cannot be brought closer than about 35 degrees to the vertical.

Figure _9-67.-Ladder ditcher.

With the ladder ditcher, excavating is done by buckets attached to the bucket line chain; the chain travels on the drive sprockets on the boom assembly. Like the wheel ditcher, the ladder ditcher has a spoil conveyor to carry the excavated material out to one side or the other. The radius of a curve depends mainly on the density of the soil to be excavated. Turns should be made cautiously at a slow-digging speed and only to where the boom starts binding between the trench walls.

The crumber shown in figure 9-68 has a major job to clean out and smooth the ditch after the teeth have cut the material. The crumber is adjustable and should be adjusted so it will clean the ditch of loose materials behind the teeth.

CHAIN DITCHER

The chain ditcher, as shown in figure 9-69, has teeth attached to a chain similar to a chain saw. The chain teeth pull or drag the cuttings to the surface, rather than lifting them in a bucket. The cuttings are usually moved back from the edge of the ditch by rotating augers.

Chain ditchers are ideal for lightweight work, such as sprinkler systems, gas lines, and small waterlines. Some of these machines can dig up to 10 inches wide and 4 feet deep.

CAPABILITIES AND LIMITATIONS OF DITCHERS

A ditcher can dig earth material ranging in texture from soft to hard; however, as the material being excavated increases in hardness, the production rate decreases. Table 9-1 gives maximum trenching rates for classes of soils in feet per minute.

A limitation of a wheel, ladder, or chain ditcher is that ramps are left at the bottom of the trench ends and around buried objects. To obtain a flat-bottom trench, you must remove these ramps by hand. The wheel ditcher digs faster in dense material and is preferred for cross-country digging where speed is needed.

OPERATING TECHNIQUES

In most ditching work, keep the machine in line and working at the proper depth. Unable to see the ditch bottom, you (the operator) must use surface controls.

First, the ditch is surveyed and the depth of cut is determined by the EAs from the blueprints. You, the EO, establish a guideline at a fixed and constant distance above the bottom grade of the trench and offset from the center line of the trench beyond the track line of the ditcher.

Figure 9-68.-Crumber.

Figure 9-69.-Chain ditcher.

The guideline should be established at a height that will put it at least a few inches above the ground at all points, stakes driven along it, and the exact height or depth of the cut marked. Then a string line is stretched along the stakes on these markings.

A rigid bar is fastened to the front of the power unit of the ditcher with one end over the string when the ditcher is centered on the ditch line. A plumb bob or other weight is fastened to the bar, so it hangs directly over the string. The operator can then keep the machine on center of the trench, cut by keeping the plumb bob just over the string. If the ground is irregular and causes the ditcher to go up and down, the cord holding the plumb bob can be run through eyes or pulleys, so the operator can reach an end of the cord to raise and lower it.

The same device (plumb bob or other weight) can be fastened on the side beam of the boom or wheel with a fixed length of string to control the depth of cut and center line travel of the ditcher.

Table 9-1.-Crawler Ditcher Maximum Trenching Rates

Cutting Curves

The radius of a curve cut while excavating a trench with the ditcher depends mainly on the density of the soil excavated. In sandy or loose soil, the radius can be much less than in hard, compacted, and rocky soil. The turn for the ditcher should be made cautiously at a slow digging speed and only to where the boom starts binding between the trench walls.