PLATE WITH TEETH | MODEL CONSTRUCTION

In the journal “modelist-Konstruktor” was published an article by a teacher from the city of Severodvinsk Vladimir Arkhipov, dedicated to the manufacture of plastic fine-grained cylindrical gears for motor car, ship and plane models on the example of gear made of polyethylene with the basic settings of m = 0.8 mm and z = 8. Continuing the theme, the author offers the readers a mold similar to the previous one, but with one fundamental difference — it is designed for making small batches of disc gears with the end location of the tooth.

In the mass modeling of such zubchatki are used quite often. For example, in the manufacture of models of racing cars. The rotation from the motor shaft to the rear axle can easily be passed, a pair of gears: cylindrical gear on the motor shaft and the Poppet (with shaft location of the tooth) mounted on the rear axle. And here, despite the seeming simplicity transfer designs, there is no easy technological task of its implementation. This is perhaps the most “narrow” place in the manufacture of models even for an experienced modeller. Of course, responsible for sports competitions models are equipped with metal gears (steel or bronze) for the manufacture of which attract professionals (as they say, in the name of victory “…for the price”). But what to do for new modelers, normal pupils 5 — 6 classes? No gears often puts an end to their engagement in the modeling.

Particularly scarce has always been considered the Cup gear. To make such hand students can not afford. Therefore, in order to support novice modelers, I have developed a simplified manufacturing technology “subcateg” of thermoplastic materials, e.g. polyethylene, by using special molds.

In this article we will focus on the casting of the disc gears. One of the most important governing parameters in the gears is the gear module m (mm). Only a gear pair with identical module can ensure the normal engagement and to be used in the manufacture of models. The basic parameters of gears defined by the formula:

m = D/(z+2),

where: D is the outer diameter of gear, mm; z — number of teeth.

The values of the modules of the gear is standardized. For gears made of metal can make a small module: 0,5 — 0,6 mm. But as the plastic, particularly the polyethylene, of strength inferior to the metals, it is necessary to use a larger module (in our case, m = 0.8 mm, z = 26), as the increasing module increases the magnitude of the tooth as a whole, and hence its strength.

The press-the form for manufacturing of plastic fine-grained disc of gears

The press-the form for manufacturing of plastic fine-grained disc-gears:

1 — base (circle 50); 2 — bottom (circle 50); 3 — liner (circle 22); 4 — matrix (round 22); 5 — housing (50 round); 6 — gear (polyethylene, polystyrene, nylon); 7 — punch (circle 20); 8 — Cup (round of 30); 9 — screw (circle 30); material det. 2, 3, 4 — brass, bronze; 1, 5, 7, 8, 9 — steel 45.

To obtain the necessary gear, and a few copies (enough for all members-modelers), design and manufacture the mold. To make it not very difficult: basically it is lathe work, small parts and suitable equipment, as a rule, in school workshops available. When making parts you should pay attention to the cleanliness and accuracy of pairing of the punch housing, and a bottom, liner and matrix depend on the accuracy and quality of finished gears. The only part that can cause difficulties in the manufacture of the matrix. At its end surface (as well as on manufactured gear) must be cut, the teeth module m = 0,8 mm. to provide the necessary quality, this operation shall preferably be carried out on special gear-cutting machine. But in the circles on the modelling of such equipment is not (in any case, I have not seen), and you can order on the side not everyone. Therefore, as a compromise, you can handle the teeth of the matrix on a conventional milling machine modular milling using a dividing head, or other similar devices. In the absence of the necessary modular cutters can be sharpened cut-off. But this is an extreme case because to get a quality tooth profile on the die, and hence to ready the gear, would be very problematic. Alas, the ordinary provincial school often makes to simplify and compromise.

So, the difficulties of the initial stage has been overcome, all necessary details molds are made and fitted to each other. You can proceed to the main — casting the desired disc gears. And this, as shown, with the availability of high-quality molds is very easy and available even to students 4 — 5th grade.

The Assembly of the mold starting with pre-lube with machine oil those parts that come into contact with plastic (it is desirable that they were made of bronze). First, in the bottom consistently set the matrix and the liner and the bottom pressed by the node base and the top screw-on housing. In his hole loaded raw materials — any thermoplastic: polyethylene, caprolactam (this material is in this case preferable since it has high strength and wear-resistant characteristics), polystyrene, etc. material is better to use in the form of granules. However, for the members to purchase granular industrial raw material — it is virtually impossible. Usually we get it from the junk bottles, toys, etc., slice them into pieces approximately the size of 2X2 mm. Required quantity of raw materials is determined experimentally: it is possible to use a scale, putting on one side of the finished part, and the other source material is by weight a little more than gear.

When the raw material is inserted into the housing the plug, spin-on glass, and in conclusion set screw. The assembled mold is placed in a muffle furnace and heated to a temperature providing a viscous-fluid state of the plastic (determined by reference or empirically). After a short exposure to get the mold out of the oven, quickly turn the screw until it stops and sharply cooled in water. After disassembling the mold, extracted gear and produce its final elaboration: cut Bleu, dulls sharp edges, etc. the result is a detail of a quite acceptable quality, suitable in the manufacture of motor models.

V. ARKHIPOV, Severodvinsk

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