With the ladder ditcher, excavating is done bybuckets attached to the bucket line chain; the chaintravels on the drive sprockets on the boom assembly.Like the wheel ditcher, the ladder ditcher has a spoilconveyor to carry the excavated material out to one sideor the other. The radius of a curve depends mainly onthe density of the soil to be excavated. Turns should bemade cautiously at a slow-digging speed and only towhere the boom starts binding between the trench walls.The crumber shown in figure 9-68 has a major jobto clean out and smooth the ditch after the teeth have cutthe material. The crumber is adjustable and should beadjusted so it will clean the ditch of loose materialsbehind the teeth.CHAIN DITCHERThe chain ditcher, as shown in figure 9-69, has teethattached to a chain similar to a chain saw. The chain teethpull or drag the cuttings to the surface, rather than liftingthem in a bucket. The cuttings are usually moved backfrom the edge of the ditch by rotating augers.Chain ditchers are ideal for lightweight work, suchas sprinkler systems, gas lines, and small waterlines.Some of these machines can dig up to 10 inches wideand 4 feet deep.CAPABILITIES AND LIMITATIONS OFDITCHERSA ditcher can dig earth material ranging in texturefrom soft to hard; however, as the material beingexcavated increases in hardness, the production ratedecreases. Table 9-1 gives maximum trenching rates forclasses of soils in feet per minute.A limitation of a wheel, ladder, or chain ditcher isthat ramps are left at the bottom of the trench ends andaround buried objects. To obtain a flat-bottom trench,you must remove these ramps by hand. The wheelditcher digs faster in dense material and is preferred forcross-country digging where speed is needed.OPERATING TECHNIQUESIn most ditching work, keep the machine in line andworking at the proper depth. Unable to see the ditchbottom, you (the operator) must use surface controls.First, the ditch is surveyed and the depth of cut isdetermined by the EAs from the blueprints. You, the EO,establish a guideline at a fixed and constant distanceabove the bottom grade of the trench and offset from thecenter line of the trench beyond the track line of theditcher.Figure 9-68.-Crumber.9-32
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