How to Change Brushes on a Bosch Rotary Hammer

The puncher is an indispensable assistant for any type of repair work. But, like everything under this sun, it is also not eternal. Sooner or later, you have to face its maintenance and repair. And the more carefully you react to it, the longer it will last.

For example, your hammer has lost power. What can it talk about? Is the tool expected to be repaired or is “its time”? In most cases, it’s okay, most likely. it’s just time to replace the brushes in the punch.

What are brushes and what are they for?

The brush is a part of the electric circuit to turn on the electric motor, the current conductor to the armature collector. Since the anchor rotates due to the electromagnetic field, there can be no fixed connection, as in a stator. The way out was realized with the help of pieces of graphite, which slides along the collector plates, thereby supplying current to the sectioned armature winding. In turn, a magnetic field is created in the winding of the latter. According to the law of magnetism, the opposite poles are attracted, this creates the movement of the anchor. As pictured below.

How to Change Brushes on a Bosch Rotary Hammer

But we can say that this is the weakest point of the collector electric motors, since the brushes are erased during operation, and coal dust clogs the collector. this leads to disruption of the normal operation of the electric motor.

The structure of the brush itself is very simple: a contact terminal, a wire from the terminal to the working surface of the brush and a spring that presses the surface to the collector plate.

With the appointment of the brushes sorted out, now consider their types. Collector brushes are of three types. In fact, there are more of them. but they are not used in rotary hammers. For example, the so-called "generator" (copper. graphite, copper. Coal) brushes.

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In the punch there are brushes of the following types:

  • graphite. a long service life, but due to the hardness of graphite, “lapping” is not ideal, and the collector suffers from this;
  • carbon brushes for a perforator. good contact with the working surface of the collector, but short life;
  • carbon. graphite brushes as an alternative to the two previous types.

Carbon Brushes for Bosch Punch

When is a replacement needed?

Typically, the working life of brushes in household rotary hammers is designed, according to the manufacturer, for 70. 120 hours of operation. But it is unlikely that the owner of the punch will keep track of the time the tool was used. In this regard, it should be noted the convenience of such a function as the wear indicator of the brush for the Makita punch. In addition, there is a tool with an automatic shut-off system in case of excess wear.

But even if you do not have such a top model, there are signs by which you can determine the increased wear of the brushes. These include:

Видео: How to Change Brushes on a Bosch Rotary Hammer


  • – increased sparking in the collector area;
  • – significant loss of power of the punch, the engine does not develop revolutions at full power.

If something like this is observed, then it’s time to take a look at the condition of the brushes and collector.

Note. Typically, for long-term use of the tool, brushes need to be replaced when their height decreases from the nominal by 1/3 (about 8 mm).

If you remove the brushes from the brush holder, you observe wear, without fail both brushes change, even if the wear is not uniform. When replacing brushes, it is strongly recommended that the collector be cleaned of graphite dust and carbon deposits. The collector can be cleaned with gasoline (preferably for lighters, its quality is higher) or ethyl alcohol. When replacing the brush, be sure to rub it into the collector. this will reduce the electric arc (arcing), which will have a beneficial effect on both the collector and the engine power. Lapping is carried out with soft sandpaper mounted on the collector. When the armature rotates, sandpaper smoothes out the irregularities of the new brushes.

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Another important nuance when replacing brushes is the degree of hardness of both the brushes and the collector. If you put soft (carbon) brushes on a hard collector. it will quickly erase. Therefore, it is important to use branded brushes from the tool manufacturer for replacement.

When replacing, you should also pay attention to the brush holder assembly itself. It consists of a profile, a clamping device and a contact group. At the same time, pay attention to the state of the spring of the clamping device, if you suspect that it is serviceable and reliable, it is better to replace it with a new one. Fortunately, it is not expensive. For example, if the spring is loosened, it will result in an insufficiently tight fit to the manifold, which will cause increased sparking. And this in turn leads to premature wear of the collector plates. And if it jumps off, it’s time to do things in the electric motor for a good repair of the tool.

By the way, if only one brush sparks, the stator may have burned down. It is easy to determine, it is important to have a device for measuring resistance. The stator has two windings, on average they have a resistance of 4 ohms each. If the resistance of both windings is the same, the stator is intact.

The replacement process itself is not worth describing, it is easy, and for most punchers, the design provides for quick and easy brush replacement like with a Bosch puncher, or any other, as seen in the video at the end of the review. Look for a special window on the case, it is usually closed with a plastic cover.

Brush replacement: do it yourself or at a service center?

The easiest option is to take it to a service center specialist, such as replacing the Hitachi rotary hammer brushes, but not the cheapest.

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Advantages of replacement in a service center:

  • – quality, if in an authorized SC;
  • – original brushes, also if the center is authorized;
  • – preservation of the guarantee for the instrument, if its period has not expired;
  • – As a rule, a full inspection of all the “vital” important parts of the instrument is carried out with cleaning and lubrication.

There are also disadvantages: you have to wait, and if it’s not warranty work, you have to pay. In addition, the service is not always close.

There is another way. with your own hand. For example, replacing the Skil rotary hammer brushes is not difficult, but.

Note. “Attempts to self-repair a tool outside an authorized service center. Unconditional signs, which include: broken warranty seals, creases on the slotted parts of the fixing screws, parts of the housing, etc. " excerpt from the instructions for the punch.

If the instrument is under warranty, it is better to take it to a service. You can do everything right, but who will give a guarantee that nothing will fail in the punch? And they will have to repair for their money. But, this is just a warning, in order not to open the tool before the end of the warranty period, usually in high-quality models with moderate use, the brushes require replacement after the expiration of the period.

What are the advantages of a do-it-yourself replacement:

  • – speed, tool at hand and ready to go;
  • – cheaper, you save on the services of masters;
  • – You do not expect a tool breakdown, its condition is always under control, just look inside;
  • – increasing the level of skill, including the maintenance of power tools.

By cons, perhaps, include the following:

  • – no guarantees of work performed;
  • – a problem with the original parts may occur;
  • – fear spoil something, and this is the loss of nerve cells.

In fact, replacing the brushes is an easy and quick procedure, besides, as a rule, rotary hammer brushes come with the tool.