The basic unit

This includes the wheels, axle, frame, cutter head, blower, and perhaps the feeding apron and rolls (referring to conventional cylinder types).

The basic unit is driven by the tractor PTO, or by an engine on the harvester.

Power Drive Systems. The PTO drive consists of a long shaft extending from the tractor PTO spline shaft to a pulley on the basic unit. This shaft has two or three universal joints. The PTO shaft assembly should have no sharp bends. Adjustable standards are usually furnished on the tongue so you can raise or lower the PTO shaft.

Follow instructions in your owner's manual in setting up universal-joint shafts because older types can be assembled incorrectly. The yokes on both ends of the telescoping shaft must be lined up alike; otherwise uneven rotation occurs on turns.

The heavy flywheel mechanism of the harvester should clear the machine of cut forage after you stop the PTO shaft. To accomplish this most machines have at least one overrunning clutch.

The overrunning clutch is like the overdrive or freewheeling device on automobiles. When force is applied to the shaft small dogs or pawls "push" the driving pulley. But when the force is removed the dogs are moved toward their hub and simply slide around within the driving pulley (Fig.8a).

The overrunning clutch is a useful device. Some makers use it on the hay hold-down wheel. Usually the hay on the apron conveyer pushes the wheel. But if the hay slips the clutch catches and moves the hay along, assisting the conveyor.

The overrunning clutch on the windrow pickup permits the drum to stand still if you reverse the feed rolls when too large a slug of forage enters the throat.

(b)

Fig. 8. (a) Typical overrunning clutch (John Deere); (b) typical safety slip clutch (International Harvester Co.)

Other clutches used on the driving systems protect the machine parts against damage in case of clogging.

The friction slip clutch is like that on standard-transmission cars and is similar to some tractor clutches.

The ratchet slip clutch will let you know when it slips. It has two hubs with sloping teeth that mesh together. They are held together by a heavy coil spring and adjusting nut. When a heavy slug stops a ratchet-protected device, the teeth slip over each other and make a noise. You can adjust the spring tension but your machine is safer if this is not too tight. You can readily identify this clutch by the teeth, the single compression spring, and nut (Fig. 8b).

The auxiliary engine's power is transmitted to the flywheel and cutter head by various methods. In some models the engine has a handy friction clutch that is used to start and stop the entire mechanism. Others tighten V-belts when power is needed from the engine. One make uses a flat belt for power transmission. Some use chains for the first stage of the power drive.

Belts are useful and practical. In the event of clogging, they slip and little harm is done. If chains or gears are used, other safety devices must be provided such as shear pins and slip clutches.

The Cylinder Cutting Mechanism. This consists of a shaft, two or three spiders, two to eight knives, and a shear plate. The spiders are fastened to the shaft and the knives are bolted to the rims of the spiders. The knives can be loosened and adjusted, usually by turning a bolt and locking the bolt with a nut. The knives can be readily removed for sharpening and for changing the cutting length.

The cylinder is at the end of the conveyor apron. Each blade or knife nearly scrapes the edge of a very sharp and hard shear plate. Since each knife is spiral-shaped, the cutting between knife and plate is a shearing action. The shear plate can be changed so that a different edge may be used when one edge dulls – it usually has four cutting edges. The edges must be kept sharp.

The cylinder mechanism has little momentum of its own. Therefore if a slug of material enters, the cylinder may stop and perhaps stall the engine, shear a pin, or slip a clutch.

One manufacturer places the cylinder on end. The lower end is close to the ground and therefore forage need not be elevated very high. The conventional cylinder is 2 or 3 feet from the ground and all material, including corn butts, must be elevated that high – and sometimes this gives trouble. The vertical cylinder, however, requires that all material be funneled to a rather narrow vertical opening. Therefore that machine has vertical cross belts to move wide windrows to the center.

One manufacturer combines the blower mechanism with the knife cutters. The spiral knives are wide and cup-shaped. This wide area propels the cut forage up and through the discharge spout to a trailing wagon.

The Flywheel Cutting Mechanism. This consists of a heavy boiler plate (Fig. 9), knife holders and adjustment devices, two to six knives, about four paddles for blowing, and a shear plate.

The boiler plate is fastened to the heavy cross shaft. It must be very well centered and balanced. Four or six sets of knife holders are riveted or welded to the plate. The knives are securely bolted to the holders so that they cannot work loose.

The knives are about 1/2-inch thick and are sharpened on the beveled side. The straight side is usually placed next to the shear plate. The knives are adjusted so that there is just a room for a piece of heavy paper between the knife and plate. This adjustment is important if the flywheel shaft develops end play; you must remove it following instructions from your owner's manual, and adjust it accurately.

Fig. 9. Typical flywheel with knives and paddles for cutting and blowing (John Deere).

The flywheel develops enough energy to force the knives through quite large slugs of forage. Hence a smaller engine can be used with a flywheel machine than with a cylinder-equipped machine of similar size.

The paddles on the wheel push the cut forage, and some air, up the discharge spout to the wagon or truck. Thus the flywheel cutter performs two tasks, cutting and blowing.

The knives on the flywheel can be taken off in pairs until only two remain, as with the cylinder type. And if a counterweight is substituted for one knife, you can run the machine with only one knife. This gives the longest possible cut without changing gears, sprockets, or pulleys.

One model that has four knives gives cuts of 1/4, 1/2, and 3/4 inches when a belt is shifted to each of three different-sized pulleys. When two knives are used, cuts of 3/4, 1, and 11/2 inches are obtained by shifting the belt. And with one knife, cuts of 11/2, 21/4, and 3 inches are secured. With this machine you can get nine different lengths of cut by changing the number of knives and feed roll and conveyor drive speeds. Feed roll drives on machines not using pulleys are varied by changing gears or sprockets.

The Feeding Mechanism. The feeding mechanism is considered a part of the basic unit, although on many machines part or all the feeding mechanism is on the pickup, row-crop, or cutter bar attachments. This mechanism consists of the conveyor apron, a hold-down apron or roll, and one or two other feed rolls.

The conveyor apron is a series of slats fastened to two or three chains. It carries the forage up to the cutting mechanism and is generally surrounded by sheet metal when an attachment such as the cutter bar is used.

The conveyor apron has many smooth or serrated slats. On a few machines a belt with rubber cross slats is used, often called a draper. It makes a tight apron, like those used on combines.

When the forage reaches the top of the conveyor apron, it must be held securely while the knives chop the stems, leaves, or stalks. Several differently shaped rolls are used for that purpose. Usually there is a bottom roll between the conveyor upper end and the shear plate. It may be smooth, ridged, or serrated.

A few manufacturers use a crawler-type upper roll. This is another conveyor apron running above the lower apron. The front of the crawler apron is held down by adjustable tension coil springs, but these permit it to rise over slugs and forces them to the cutter.

Many machines have large serrated rolls to hold the forage down and move it to the rear. Some use a drum with retracting steel fingers. Others have two upper feed rolls, with the rear one smaller than the front.

All the feed rolls are power-driven. The driving mechanisms are protected by slip clutches, overrunning clutches, or slipping V-belts. It is desirable to be able to reverse these feed rolls if the throat becomes clogged. The feed rolls and apron are both reversed at the same time, thus readily clearing the machine.

The throat is the space through which all forage must pass before being cut. The width of the throat gives some indication of capacity, but there are other factors to consider also, such as engine power and overall size.

The feed rolls are held down by adjustable springs but can move up and down to a certain extent. Self-aligning ball bearings are often used because of the twist that the upper rolls receive as they pass over uneven piles of forage.

Part V