How to make a big sprocket for a bike. What can be done from unnecessary parts of the bike

How to make homemade sprocket block for bicycle. The road bike is simple and reliable. It has a trouble-free foot brake, which is important when driving off-road, but there is no gear shift, as, for example, in multi-speed bicycles of the “Tourist” type, which is so necessary when driving over rough (with hills and ravines) terrain.

However, the "Tourist" has only a handbrake, which, in my opinion, has neither smoothness, nor reliability, nor wear resistance, and it costs much more. Is it possible to combine the advantages of both types of bicycles? It turns out that if you think about it, it is partially possible by installing on the road instead of the standard driven sprocket block of three coaxial sprockets rigidly fastened (welded) through spacer wire rings.

First (small) star, having 18 teeth, regular. It is hardened, therefore, for subsequent welding into a block, it must be released, that is, heated on fire (in a fire or over a gas burner) to red and cooled in air. The second and third sprockets, respectively with the number of teeth 24 and 28, are self-made. They are made of 2.3 mm thick sheet steel using the following technology. On a small sheet of drawing paper, a circle is drawn with a compass (for the second asterisk with a diameter of 97 mm).

Then the paper is placed on soft cardboard (or several layers of newspapers). Part is placed on the sheet bicycle chain(24 links) so that the centers of the axes of its links are located approximately on the drawn circle, and the distance between the axes of the first and last link is equal to the chain pitch - 12.7 mm.

This part of the chain is carefully covered with a piece of plywood sheet and through it is pressed against the drawing paper by hand. The prints of the axes will remain on the paper. Then this imprint is glued onto the steel sheet and through it on the metal, in the middle of the printed circles from the axes, the centers are punched and 24 holes with a diameter of 8.5 mm are drilled.

Next, a sprocket blank is cut out of the steel sheet with a chisel or hacksaw. It remains only to mark according to the template, carefully grind each of her teeth on an emery and file, and also make a central hole with a diameter of 51 mm. The third sprocket was made in the same way, only the diameter of the circle on the drawing paper was 112 mm and 28 chain links were laid on it. In place of this asterisk, you can install and ready from the old children's bike- it has the same number of teeth with the same pitch. Only before welding it also needs to be released.

Two annular spacers with an inner diameter of 52 mm are bent from 6 mm steel wire. Before connecting the sprockets into a single block, for the convenience and reliability of welding them with rings, several technological holes with a diameter of 12 mm were drilled in self-made sprockets. After that, having ensured the coaxiality of the sprockets to prevent the beating of the gear rims, the rings and sprockets are sequentially welded to each other with points evenly distributed around the circumference.

The manufactured block of sprockets is planted on the outer part of the leading cone rear hub bicycle and a regular (smaller) sprocket is welded to it in a circle with a reliable continuous seam. It would be possible to simply fix the block with a "native" spring ring, as usual, but there is no guarantee that the thermally tempered splines of the small sprocket will withstand the increased loads. For welding work, the driving cone is released from the bearing and rollers and thermally released in the same way asterisk. Re-hardening of the part, as shown by the operation, can be omitted.

The axle length is enough to fix the drive wheel with the sprocket block in the rear fork of the bicycle. But no matter how hard I tried, I could not design a simple and reliable home-made gearshift mechanism. Therefore, I installed a standard mechanism from the old Tourist bicycle on my road builder, rigidly fixing it with an M10 bolt right in the frame hole.

The gear lever is located under the seat. For those who do not have such a speed switch, I advise you to prepare two pieces of chain with locks at both ends: the first with five links, the second with nine. Then, before the next trip, even at home, you can lengthen (or shorten) the chain and put it on the desired sprocket, depending on the intended nature of the route, speed and your physical form.

For example, if you have to travel light on the highway, then a smaller sprocket and a shorter chain (without inserts) are selected. When it is necessary to overcome the path along a country road, and even with a load, a long segment is inserted into the chain - for a larger sprocket.

Star block on the drive cone of the rear hub road bike: 1 - small sprocket (z = 18, t = 12.7, from a road bike); 2 - intermediate sprocket (z = 24, steel, sheet s2.3); 3 - large sprocket (z = 28, steel, sheet s2.3); 4 - ring distance inserts (steel, wire with a diameter of 6); 5 - leading cone of the bushing; 6.12 - anthers; 7 - tip of the rear fork of the bicycle; 8 - axis; 9 - nut; 10 - washers; 11 - fixed cone; 13 - bushing body; 14 - cup; 15 - leading roller; 16 - bearings

Making an asterisk

Making an impression: 1 - drive chain; 2 - paper sheet

Welding of distance inserts with an asterisk through technological openings: 1 - an asterisk; 2 - remote insert

Instead of a round drive sprocket, an elliptical sprocket was proposed to be used on a bicycle back in 1892 by Professor V. Prusakov. He decided to place the cranks along the minor axis of the ellipse, which made it possible to more rationally use the forces of the cyclist. Experiments have shown that even an inexperienced cyclist on a car with an elliptical sprocket spends approximately 30% less energy than on a cycle car with a round one moving at the same speed.

asterisk. And according to American engineers, the use of an oval gear increases average speed cyclist by about 14%.

But, despite all this, the non-circular sprocket was not widely used either in our country or abroad: the bicycle industry was not ready for the production of non-traditional chain drive elements.

However, it is not so difficult to calculate and make an elliptical sprocket on your own. It is only necessary to take into account that its effectiveness depends on the ratio of the major and minor axes of the ellipse: the larger it is, the more advantageous its use is. Considering this and the design features of the bicycle, the maximum size of the large axle and the minimum size of the small axle of the sprocket are determined. Then you have to

where 12.7 is the pitch of the bicycle chain, n is the number of teeth of the elliptical sprocket (selected by the same method as for chain drive with round stars). The length of the ellipse is calculated by the formula:

where a is the major axis of the ellipse, b is the minor axis of the ellipse. Having chosen the size of one of the axes of the ellipse, we find the value of the other axis of the ellipse. It must be such that it matches L** to the second decimal place. \ "On a sheet metal workpiece from which the sprocket will be made, an ellipse of roller centers is built according to the formulas:

where a is the major axis of the ellipse, b is the minor axis of the ellipse; x and y - Coordinates of the point relative to the center of the ellipse; a = 0°, 10°, 20° …… 360"

Further, this closed curved line is divided using a compass into n equal parts with a step of 12.7 mm. Now it will be no more difficult to cut an elliptical star out of metal than a round one. Studies have shown that the efficiency of the ellipse sprocket increases if the minor axis of the ellipse “lags behind” the connecting rod by 10 ° ... 25 °. For sports and sports-tourist bicycles of the Kharkov Bicycle Plant, an elliptical sprocket with 46 teeth and axle sizes a = 110.18 mm, b = 73.981 mm with a ratio a / b = 1.49 was calculated and manufactured. The lag of the minor axis of the ellipse from the connecting rod is 15 °. All other dimensions of the sprocket are shown on the drawing.

And now the most interesting!

One of my readers made an asterisk according to the drawings of this article:

Here is what he writes:

Operational properties and manufacturing principle read here . From myself I will say that the effect simply shocked me, I did not even imagine this. For example, on a forward with a gear of 28-34 (front-rear chainring) I drove up a very steep and long mountain and wanted to fall and not get up, my tongue was on my shoulder, my legs fell off. On this lisapede, after installing elliptical stars with a gear of 32-28, I drove up the same mountain and even my breathing didn’t go astray, my legs felt much less stress. Moreover, the speed of movement up this mountain on the forward is 6-6.5 km / h, and on this 7.5-8 km / h !!! And in a straight line on asphalt, the speed of movement increased.

Stars - transmission units for the chain transmission of forces from the cyclist's legs to rear wheel. Asterisks for a bicycle play a paramount role - without them, he simply will not go. Single-speed models are supplied with a pair - leading and driven stars. Bicycles with multi-speed transmission are equipped with speed dials in front (system) and rear - ratchet or cassette.

The number and size of the sprockets determine the bike's flexibility in various road conditions. Thanks to the correct gear ratio, you can significantly reduce the energy consumption for a trip and move at a comfortable speed. The durability of the parts depends on the quality of the material, the style of riding and the quality of service - with proper care, even "initial" stars will last longer than professional, but neglected ones.

Gear ratio of driving and driven stars

Stars on speed bikes located on the right connecting rod (drivers) and the rear wheel hub (driven). Through the chain is the transmission of forces from the front gears to the rear. Interestingly, the rear wheel, on the contrary, is leading, and the front wheel is driven.

The gear ratio is the difference between the size and number of teeth on the stars. This parameter directly affects the speed of movement and transmission power. A high gear ratio is provided by a large drive and small driven gears, a low gear ratio, on the contrary, is provided by a small front and large rear sprocket. Accordingly, the gears on a classic transmission in the first case are 3 x 8, and in the second 1 x 1.

The larger the chainring, the higher the speed. For example, the front has 44 teeth for chain engagement, the back has 11 teeth. For one revolution of the pedals, the rear gear will do 4 revolutions. If we take a gear of 22 to 11, then only 2 revolutions of the wheel will be made in one revolution of the pedals. In low gears, the opposite situation is observed: the chain is on a 22-toothed gear in front, and 32 on the back. The gear ratio is less than 1, that is, for 1 revolution of the pedals, the wheels do not have time to spin completely.

High gears are designed for fast movement on a flat road. On hills, in headwinds and in poor road conditions, lower gears are used - the speed of the bike is lower, but more power and less energy consumption. Often, gears with an average star ratio are used, for example, 2 x 5 and 2 x 6.

Each star in the system has its own range on the cassette. It can "float", that is, the same reverse gear applies to two stars of the system at once, but, in principle, the pattern is as follows:

Scheme of the optimal ratio of gears for different driving modes

collapsible on a single drum with separators;
on a spider;
on blocks (several spiders);
Open slide;
X-Dome.

The first type of cassette is the simplest - all stars are installed on a single slotted drum. They are separated from each other by partitions - spacers. The disadvantage is the constant load on the drum. But the undeniable advantage is that they are easy to disassemble and change one sprocket. They are easy to clean, but the components get dirty more often.

Spider - a light version of a collapsible cassette. The load on the drum is not so big - here it does not come from every star, but only from the slotted spider mount. These cassettes are lighter and less likely to get dirty.

The design on several spiders includes several pairs plus small stars separately attached to the drum. The model is very convenient because it is easy to pick up a new block and, unlike a collapsible analogue, you do not have to fiddle with spacers for a long time and lay out the entire cassette. The development of this piece belongs to the Japanese parts manufacturer Shimano.

Open Glide is a one piece set that fits over the largest gear. Unpretentious model: thanks to high-quality material less wear, long service life, low weight. True, it is problematic to clean a heavily soiled cassette.

One-Piece SRAM X-Dome Gear Set

A similar design is represented by the X-Dome system. Here both large and small stars are in contact with the drum. A whole-milled block of 7–8 stars is mounted on them. Both Open-Glide and X-Dome are owned by SRAM.

How to clean and lubricate sprockets

Friction mechanisms require periodic lubrication and cleaning from dirt. This will improve ride quality and extend the life of the transmission. Classic single-speed models often include chain guards. It is recommended to leave it. It also keeps the front sprocket free of dirt.

Already after several rides through the forests, crossroads and off-road Mountain bike overgrown with dirt. And if it is clearly visible on the wheels and frame, then it is not always in the mechanisms. Therefore, you need to inspect your two-wheeled horse more often and take action in time.

Cleaning the bike cassette:
1. Release the rim brake (remove the caliper on the disc brake), remove the rear wheel.

2. Check for dirt. If everything is very bad, you will have to remove and disassemble the cassette. With minor contamination, you can clean directly on the wheel.

3. Special narrow brushes are better used for cleaning. They allow you to get into the deep gaps between the gears and find a lot of interesting things there. Yes, and much more convenient than climbing into the gaps with a rag.

4. You can clean the teeth with an old toothbrush or wipe off the abrasive with a soft cloth.

5. After that, wipe the surfaces with kerosene, allow to dry and apply lubricant to the teeth and pits. It is recommended to clean and lubricate the chain at the same time as the cassette. Only in this way will it be achieved desired result.

Cleaning the system is done by analogy. Everything is simpler here: you don’t need to remove the wheel, just a few stars. True, you need to work carefully so as not to damage or upset the switch.

Asterisks are the most important components of the transmission, without which movement is impossible in principle. Proper selection of gears, periodic cleaning and timely replacement of worn components will avoid unpleasant surprises on the road, and, indeed, will be high-speed, and not drive in only one gear.

In fact, absolutely anything can be made from bicycle parts. This is not always appropriate, it is not always practical, the result does not always look great, but with free time and materials, everything is really possible.

Let's look at the main categories of such crafts:

Art;

Disposal;

Desire to surprise

Urgency;

In our article, we looked at various categories, and also wrote an approximate list of parts that would be required to reproduce an idea.

Which of the ideas belongs to which category, we are sure you can guess.