Care of Farm Mower

New Zealand Journal of Agriculture, Volume 81, Issue 5, 15 November 1950, Page 433

Care of Farm Mower

THE farm mower, which is probably one of the most common implements on New Zealand farms, is a machine which requires regular attention to the sharpening of the knife as well as a thorough overhaul once a season if it is to work with maximum efficiency. This article by D. F. Scott, Farm Machinery Instructor, Department of Agriculture, Auckland, describes the main points to be watched by the user if he is to get the most satisfactory results from his machine.

THE bodies of the first motor-cars were adaptations of the horsedrawn buggy, using an engine instead of a horse for motive power. As time went on they gradually changed until the, body of the modern car is altogether different from the prototype. Similarly, the mower, which is being adapted to the tractor instead of the horse, is undergoing changes which may not yet be finalised. The first tractor mower was simply a horse mower drawn by a tractor. Later the trailer mower was driven from the power take-off to enable the blade to be driven at high speeds independent of the ground speed, and later still came various forms of tractormounted mowers, some with cutterbars in front of and some behind the rear wheels of the tractor. Some of these mowers are fitted with either one or two castor wheels, and cutterbar lengths. vary from 4ft. 6in. to 7ft. The, main details of the cutting mechanism of these machines are similar, so that with only a few exceptions the maintenance is the same as that required for the horse' mower.

A mower in bad repair means up to 35 per cent, increased draught, loss of time through having to clear blockages, and a poor job done, so time spent on overhaul and repairs during the off season will save valuable time at haymaking later. A mower in good condition should have only a very slight side draught, but once the knife becomes blunt or the cutting mechanism becomes defective in some way the side draught increases enormously. With the horse mower it. was most necessary to keep the cutter-bar in good order to make the job as light as possible for the horses, but there

is a tendency with power-driven machines for the operator to neglect the condition of the cutting mechanism and when the going gets hard merely to open the throttle an extra nick and carry on, with the result that the very heavy side draught on the cutter-bar is likely to strain or break the yoke casting at the head of the cutter-bar. Power mowers which have been damaged in this way are quite common and the result is that the cutterbar lags behind its correct position and also the pitman rod and knife run out of line. Sharpening the Knife

A . dull or improperly ground knife causes ragged cutting, rapid wear, and extremely heavy draught. The quickest and easiest way to sharpen the knife is on a power-driven emery wheel. A specially shaped stone is available for the job and this should be dressed periodically with a dressing tool to preserve its correct shape. There are also available hand-driven grinders which can be clamped on to the wheel of the mower and are so designed that the stone moves up and down the cutting edges of the knife, which is held in position by a clamp. Another very convenient way to sharpen the knife is to use one of the specially shaped emery wheels mounted on the end of a flexible shaft. Although a file can be used for the job, the steel of the section is so hard that a new file does not last long. Whichever way the sections are sharpened it will be necessary to remove the feathered edge, which will damage the cutting surfaces once the knife is replaced in the mower and

comes into close contact with the ledger plates. Points to Watch Points to watch when sharpening mower knives are as follows: — 1. Maintain the original width of bevel. A narrow, blunt bevel does not cut well, and a wide, keen bevel is too easily nicked in use. 2. Maintain the original angle of shear. Try to grind the new cutting edge parallel to the old one. 3. Do not overheat the metal and draw the temper. To guard against this it is necessary to keep the section moving on the stone and not to apply too much pressure. Any sections that are badly worn or chipped should be replaced. The knife can be held in a vice and the old section removed by cutting the rivets with a cold chisel. The practice of levering the old section off is inclined to distort the rivet holes in the knife bar. When riveting the new section on place the back of the knife on an anvil and swell the rivet with a few heavy blows and then round off the end. Do not overdo the rounding off and spread the head of the rivet, as this merely weakens it. With the older American type of mower it is better to buy a new knife rather than to replace all the sections on the old one. However, with the new English models the difference in price is too great. The knife should be examined periodically for loose rivets, especially in the knife head, where there is more vibration and wear. Cu+ter-bar Parts Sharpening the knife has little effect if ledger plates are in bad condition. Ledger plates, which are replaceable hard steel plates with serrated . edges and which fit on to each finger to form the cutting edge, are not found on later British models imported to this country. Instead, the finger is made of a harder steel and has a nonreplaceable smooth cutting edge. It is stated that this type has been used in England for a number of years and has been found quite satisfactory there. Ledger plates which are worn smooth or round on the surface should be replaced. The finger should be held firmly and the rivet punched out. When the new plate is being fitted make sure it fits well into its position. It may be necessary to grind a little off the plate to do this. When the new plate has been riveted into place make sure that none of the countersunk rivet head projects above the surface of the plate. After all the ledger plates have been inspected the fingers must be adjusted so that the ledger plate surfaces are in line. A piece of light cord can be stretched across the surfaces of all the ledger plates to check the alignment and the fingers can be bent up or down by hammering the thick part of the fingers or packed with thin shims to raise or lower them. The knife clips should be hammered down so that there is about l/32in. between the clip and the knife and the wear plates are slid forward to force the points of the knife sections down on to the ledger plates. Adjust the wear plates so that they do not bind but just have a working clearance.

Before hammering down knife clips remove the knife from under the clip, but slide it back to check the clearance of each clip. It is important that the sections should rest square, level, and hard down on the ledger plate, and it may be necessary again at this point to raise or lower slightly, individual fingers by hammering or by using a piece of pipe as a lever. If the knife-head guides are allowed to get' worn, excessive vibration and chattering of the knife head occurs and this is likely to be the cause of a broken pitman. The knife-head guides can be adjusted by removing shims from beneath them so that there is only a good working clearance between the knife heads and the guides. If a knife is bent, it can be straightened by hammering it on a flat surface. A bent knife will bind and so increase the wear and also the

friction. The knife should be carefully inspected for bends, flatwise or edgewise. Fitting New Fingers When fitting new fingers to the cutter-bar make sure that the wings of the finger each come into contact with a wing on the two neighbouring fingers. These wings ensure that the finger is held firmly in its correct position. If the wing is too long, a little should be ground off it, or if it is too short, it can be drawn out by hammering it on an anvil. Adjustable skids on both the inner ana outer shoes will become worn in time, but these can be built up by welding or replaced. The Lead Angle The cutter-bar when not cutting and with the mower at rest does not project exactly at right angles to the path of the mower. A small amount of

lead is applied so that the outside end of the cutter-bar is slightly ahead of the inside end. This lead is approximately Jin. for every foot of length of the cutter-bar; that is, for a 4ft. 6in. bar there would be about Igin. lead and for a 6ft. bar about Ijin. As the mower becomes worn this lead will decrease so that there will probably be a lag and this will also mean that the pitman rod and the knife are not in the straight line which is required when the mower is at work. This lag is very often due to worn hinge pins and these can be built up or replaced. On some mowers the rear hinge pin is fitted with an adjustable bush, or the lead can be altered by adjusting the lengths of the push and tie rods. To check the lead of the cutter-bar set up the mower in the cutting position on a flat piece of ground. If it is a horse mower, raise the pole and support it in the cutting position, that is, about 32in. above the ground, and pull back on the cutter-bar to take up any slack. Tie a string, to the head of the pitman rod and run it out over the knife, keeping it parallel to the pitman. Then check the lead angle. Register

The register should be adjusted so that at the end of each stroke the centre of each section of the knife should coincide with the centre of the finger. . The main ’ thing that determines the register is the length of the pitman rod. The pitman may have been replaced by one that is not the correct length or perhaps it is of the metal type which is adjustable in length and requires adjusting. The register can also be altered by lengthening or shortening the tie bars and shifting the yoke washers. Lubrication Lubrication or the lack of it is one of the chief factors determining the length of life of a mower. The wrist-

pin bearing on the crank wheel should receive frequent lubrication while working. It is worth while stopping to grease it every Ig hours. The gearbox should be filled to the level of the crank shaft with a good brand of gear oil. Care should be taken to see that no water is allowed to enter it. The oil should be drained out and replaced at least once a season. All the other lubrication points should receive daily attention, but .on mowers with V-belt

drives no oil should be allowed to get near the belts. A drop of oil applied to all the points in the usual complicated system of levers which raise and lower the cutter-bar will make for easier operation and reduce wear. The hinge pins should also be oiled. Safety Release Most tractor-mounted mowers are fitted with a safety release which will allow the blade to swing back if it strikes an obstacle. The release should be adjusted so that it will release before any damage is done. Similarly on all power mowers the slip clutch should be adjusted so that it will slip as soon as any part becomes jammed or broken and before any further damage is done. The balance spring on the lifting mechanism should be correctly adjusted. This spring reduces the effort required to raise the knife and also reduces the weight on the outer shoe and thereby cuts down the draught. If this spring is adjusted too tightly, the outer shoe will tend to rise ana will not follow the contour of the ground. On the other hand, if the spring does not have enough tension on it, the knife will be very difficult to raise. Most makes of mower provide in different ways for the. various adjustments mentioned earlier, so that the best source of information on any machine is the operator’s handbook. and this should be referred to when any trouble is experienced with the machine. Worn Bearings The machine should be inspected at intervals for worn bearings. These are easily detected when there is side play in any of the shafts that drive the knife. Worn bearings should be removed and new bearings should be carefully fitted in their place. The pinions and gears in the gearbox should also be examined to see that

they are - meshing to the required depth. These should be meshed fully, but not to such a depth that they will bind. If the gears are unduly noisy after adjustment, it is an indication that they are meshed too deeply. The meshing of the gears can be adjusted by the fitting of washers between the bevel gear and the frame or by the adjustment of set screws for this purpose. Wheels and Pawls On the horse mower the pawls and pawl springs in the wheels should be inspected for wear and breakages. If they are allowed to become worn so that the pawls slip, the ratchets are

damaged and are difficult to repair and expensive to replace, as they are a part of the wheel. Excessive end play in the wheels allows the pawls to lean outward and causes uneven wear to the pawl holders and the ratchets. The take-up washer on the outer end of the hub can be adjusted to reduce end play and if it is still excessive, steel washers can be added between the hub and the take-up washer. The ratchet, pawls, and springs in the hand lift lever of the tractor mower should be examined regularly to make sure that they are operating easily and that the pawl and ratchet give a lock which cannot be shaken loose.

Storage Where possible the mower should be placed under cover and the blade should be removed, sharpened, and covered with a film of thick oil. ' All shiny parts such as fingers and other cutter-bar parts should be covered with grease, and if the machine is mounted on rubber, it is a good idea to take the weight off the wheels by supporting the mower on blocks. Whether the cutter-bar is fixed in the vertical position or in the working position when the machine is stored, it is a source of possible injury unless the points of the fingers are shielded by wrapping them with bags or by placing a piece of wood in such a position as to cover all the points. Knives should be stored out of the weather and in a place where they will not be a danger to man or animal. Safety Precautions The mower is undoubtedly a dangerous machine if not used properly, or if the user takes risks. The following points are worth noting: — 1. Never dismount while the mower is in gear or while the power take-off is running. 2. With a horse mower, never clear the cutter-bar with the hands or stand in front of the cutter-bar. 3. Always use power take-off shields and belt or chain covers and do not wear a scarf or long loose clothing. 4. Do not allow children or dogs in a paddock while it is being mown. SUBSCRIPTION RENEWALS Renewals of subscriptions to “The New Zealand Journal of Agriculture” should be paid to the nearest office of the Department of Agriculture. Subscribers can ensure continuity of delivery by paying their subscriptions as soon as possible after receiving their renewal notices and at least 1 month before the old subscription expires. When payment is made the renewal notice should accompany the subscription to ensure that the correct details are recorded.

CARE OF THE FARM MOWER

CARE OF THE FARM MOWER

CARE OF THE FARM MOWER