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BUILDER, HOUSEHOLDER
Milling cutter in the garden. Tips for the home master
Directory / Builder, home master A. Mikhranov built his first motor cutter in 1981. As a prototype, I used the development of my friend Peter Koinov. Although he did a lot differently: engine mount, steering wheel, bearing installation, three-stage gear train, and so on. Tests, however, revealed shortcomings: the engine was overloaded due to the low gear ratio and large diameter of the cutters; The inclined blades of the cylinder head cooling fans broke off three times. After the speed of the cutter block was reduced to 82-85 per minute and other problems were eliminated, the machine began to work flawlessly. Over the years, the cutter has been repeated many times. Only in the Yambop district now there are about five ten such structures. Indeed, the unit turned out to be quite technologically advanced. Only 15-20 parts need to be made in the workshop. All the rest can be done at home using a drilling machine and an electric welding machine. In addition, some parts - such as distance tubes - are made on a drilling machine (if other machine equipment is available, the design of the tubes can be simplified).
In most cases, preference is given to finished parts: a gear, a faucet, a throttle handle, a fuel tank and many other factory components. Many of those who took up the repetition of the cutter also made trailers for transporting goods of 250-300 kgf. They claim that on a flat road and in third gear they reach speeds of 18-20 km / h.
Now about the features of soil cultivation. The assertions of some amateurs that. it must be well plowed beforehand with a large tractor, that it is impossible to mill the uncultivated heath, is unreasonable. Difficulties appear only with tall grass or when working with very caked and dried soil. But it is enough to mow and remove the grass from the site so that the motor cutter (with sufficiently wet ground) works confidently. Moreover, when the author recently had to dig a watering hole with a diameter of about two meters and a depth to the waist, he used a motor cutter seven or eight times, and threw it into the ground with a shovel. This convinced him that if only two knives (about 4 cm wide) were left on the cutters, then even ditches could be dug, say, for an electric cable. True, the motor cutter had one significant drawback. When working dry soil, the air-cooling fan sucked in dust that got into the ignition switch contacts, and the engine stalled. I had to remove the casing and fan blades and clean the contacts. This took 5-10 minutes.
The problem was solved with the help of a corrugated air intake pipe. Now the air comes from a height of about half a meter above the ground, which prevents dust from entering the interrupter. A few words about the engine itself (from a motorcycle). The cylinder has been polished to the second repair size, and thus its working volume has increased. As a result, the rated power has increased to approximately 4 ps. The ignition timing according to the passport should be set from 1,1 to 1,2 mm from the top dead center (8MT). The author set it with the help of an indicator that gives accuracy to hundredths of a millimeter, 1,75 mm before TDC. After that, the engine began to work very steadily.
The transmission bearings run in Lubrication, as does the chain itself. On fire, 400-500 g of ordinary grease is heated and poured into the chain box of the frame. Until it thickens, the chain is turned several times to lubricate it along its entire length. The cutter has easy control that does not require much physical effort. In order not to trample the cultivated soil. The operator walks from the side, holding the machine with one hand. The productivity of the machine is approximately the following: 35-40 minutes are spent on a vineyard with an area of five acres at a milling depth of 15-20 cm, fuel is consumed about 1.2 liters per hour.
The ratio of gasoline and oil in it is 20: 1. A slightly increased oil content in the mixture is quite acceptable for two-stroke engines. Together with good cooling, this allows you to work for hours in the August heat without overheating the engine. And now about the design of individual components and parts of the motor cutter, about how and what they are made of. Let's start with the frame. Both her cheeks are cut out of sheet steel 4 mm thick. A rectangular viewing window was made only on the left of them. Then both cheeks are baited - connected by several points of electric welding with a girdle strip, and then processed together. Holes with the specified dimensions are turned with a boring bar.
The top and bottom races of the bearing units are welded to their respective bores using guide washer sets and M18 mounting studs. One kit is designed for mounting the lower rings, the other for the upper ones. After the welds had cooled, the studs AND washers were removed, the edges of the hole were machined with a sharpened triangular Faber so that the bearing housings fell freely into place. The gap between them is about 0,10-0,12 mm. This operation is time-consuming and required special care. All rings are cut by a gas burner from sheet steel 8 mm thick and turned on a lathe. The holes for the bolts are drilled in advance, before welding, and only then the thread is cut. Moreover, the upper bearing housings with their races are drilled at the same time to ensure alignment of all 24 holes. M8x20 bolts entered them freely and are easily screwed. In total, they needed 24 pieces.
Frame welding. The rings of the upper bearing units are mounted in the same way as the lower ones, with the only difference that the mounting sleeve was held not by one inner one, but by two outer studs and two U-shaped profiles, since the left bearing housing did not have a central hole. All studs (two upper and one lower) are tightened to failure, the cheeks are girded with a steel strip 34 wide and 5 mm thick and connected by spot welding with a step of 50 mm along the entire length. Then the final assembly of the frame began, and after applying a seam 60-80 mm long, welding was interrupted and a similar seam was applied on the opposite side of the cheek. This is done so that the entire frame does not warp and the work is not in vain. After the metal had cooled, the studs and bolts were unscrewed and the bearing housings removed. But not earlier, because when welding, the holes in the rings under them could be deformed, and then scraping would be required again. Mounting sleeves (false bearing housings) are used when assembling the frame in order to obtain full alignment of the bearing housings of both the lower gear shaft and the upper one. Without them, the cheeks of the frame warp during welding - twist. The end surfaces and external diameters of the bushings are machined in one setting in the spindle of the turning wall with the right and left cutters. Therefore, for the lower sleeve, two strips with central holes d 16,1 mm are welded into the thick-walled pipe in advance. The quality of the frame depended to a large extent on the accuracy of processing false cases. Further, a transverse bracket and an engine mount support were welded to its main box. The cuts in the bracket were made with a finger cutter d 10 mm. The support is welded from strips of steel 30X4 mm. The sight glass cover is cut from 2 mm thick sheet steel and attached to the frame with four M4X6 bolts, sealed with sealant - it is removed once a year to check the condition of the main chain. Lastly, two steel cubes with a side of 10 mm are welded in | mm from the upper cut of the main kolobok. Holes were drilled in them and threads were cut for M6x6 screws of the cover, through which the main target was passed and About the main shaft-gear. It is made of 40X steel with subsequent heat treatment. He has 15 teeth - with the same pitch as the main chain (19,05 mm). You can also use a ready-made gear, if there is a suitable one. The holes in the ends of the shaft-gear wheel d 7,5 mm were drilled using a jig. It should also be used in the manufacture of remote bushings, which of all parts of the motor cutter are subjected to the greatest loads. All holes d 7,5 mm were drilled from one sharpening of the drill. When drilling, the center marking with dots was preserved so that the pins of one bushing freely entered the holes of the other. The ends of the bushings are perpendicular to their longitudinal axes. When planting the pins, a packing device was used. The depth of the axial hole in it is exactly 12 mm - this is especially important during installation. The device did not harden. It is also important that the tolerance on the left side of the pins is maintained within the specified limits. Strips of remote bushings (six pieces) - made of steel 3 with a thickness of 5 mm. The hole, spaced 73 mm apart, is drilled to the tolerances shown in the drawing. Otherwise it would be impossible to achieve interchangeability of cutter blades. The assembly sequence of each spacer sleeve is as follows: first, the pins of the left ends were pressed in. Then a bar was welded 10 mm from the edge of the sleeve, and only then holes were drilled in the right end. Engine mounting brackets are made of steel strip 30x10 mm. All the indicated dimensions are maintained exactly: the axes of the holes had to coincide with the axes of the welded nuts. The muffler is made from a piece about 200 mm long from the muffler body of the Balkan-50 motorcycle. Its bottoms are cut from sheet steel 1 mm thick. The remote partition - of the same thickness and with a diameter 9 mm less than the inner diameter of the muffler body) is riveted to the bottom with an outlet with three special rods located at an angle of 120 ° to each other. And only after that the bottom was welded into the body with a gas burner. With such a silencer, during operation, the moto cutter is no more than from the Druzhba-4 chainsaw. The material of the gear wheel hub is steel 45. The trunnion of the upper shaft-gear wheel fits tightly into the hole of the hub. The radial runout of the holes d 28 and 60 mm and the end runout of the front surface from the side d 60 mm is minimal, since the author processed them on a lathe in one installation; hole d 8 mm drilled simultaneously with holes in a large gear wheel with 45 teeth.
The upper housings of the bearings are soaked from cast iron. One of the design tricks is hidden in them: the bearing seats are machined with a 10-millimeter offset relative to the central axis, which makes it possible to adjust the chain tension. Here you need to pay attention to the following points: the most accurate alignment of the axes of the holes in the cases and the same exact drilling of 24 holes in the upper rings of the frame box. It was necessary that the bearing housings could be installed in increments of 15° around the circumference (to change the tension of the main chain). The material of the shaft-gear wheel is steel 40X. The wheel is heat treated by quenching in oil when heated to 633° and tempered to HRc = 45-47. The upper eye of the frame consists of a bushing (steel 45), a strip of 20x6 mm and a rib made of sheet steel 4 mm thick. When connecting the lug to the frame, it must be remembered that the axis of the hole d 18 mm must be perpendicular to the horizontal traverse. All parts of the rear support are made of steel 45, with the exception of the axle, which is made of steel grade Kh12 or 35KhGS with subsequent heat treatment. The original parts of the steering wheel are two toothed washers, three half-inch pipes and a 30x30 mm bar. The M12 mounting bolt shown in the figure is only used to weld one of the toothed washers to the bar. The second washer is welded to a corner bracket machined from a piece of 45 steel. Welding is done using the same mounting bolt. Connected with an M12x65 bolt, the washers engage with each other and allow you to adjust the height of the steering wheel depending on the height of the operator.
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