Mini drill with adjustable speed

Automatic speed controller for mini drill.

When working with lead-out components, you have to make printed circuit boards with holes, this is perhaps one of the most enjoyable parts of the job, and seemingly the easiest. However, very often, when working, a micro drill has to be put aside, then pick it up again in order to continue working. A micrill lying on the table when it is turned on creates quite a lot of noise due to vibration, moreover, it can fly off the table, and often the motors heat up decently when operating at full power. Again, vibration makes it difficult to aim accurately when drilling a hole and it often happens that the drill can slide off the board and make a furrow in adjacent tracks..

The solution to the problem suggests the following: you need to make sure that the micro drill has a low idle speed, and under load, the drill speed increases. Thus, it is necessary to implement the following operation algorithm: no load – the chuck rotates slowly, the drive got into the punching. the turnover increased, it went right through – the turnover fell again. The most important thing is that it is very convenient, secondly, the motor works in a light mode, with less heating and wear of the brushes.

Below is a diagram of such an automatic speed controller found on the Internet and slightly modified to expand the functionality:

mini, drill, speed

After assembly and testing, it turned out that for each engine it was necessary to select new ratings of elements, which is completely inconvenient. We also added a discharge resistor (R4) for the capacitor, since it turned out that after the power was turned off, and especially when the load was disconnected, it was discharged for quite a long time. The modified schema looked like this:

The automatic speed controller works as follows – at idle speed, the drill rotates at a speed of 15-20 rpm, as soon as the drill touches the workpiece for drilling, the engine speed increases to maximum. When the hole is drilled and the load on the engine decreases, the speed drops again to 15-20 rpm.

The assembled device looks like this:

A voltage from 12 to 35 volts is applied to the input, a micro drill is connected to the output, after which the required idle speed is set by the resistor R3 and you can start working. It should be noted here that the adjustment will be different for different engines, because in our version of the circuit, the resistor was abolished, which was required to be selected to set the threshold for increasing the speed.

It is advisable to place the T1 transistor on the radiator, because when using a high power motor, it can get quite hot.

The capacitance of the capacitor C1 affects the delay time for turning on and off high speed and requires an increase if the engine is jerky.

The most important thing in the circuit is the value of the resistor R1, the sensitivity of the circuit to the load and the overall stability of operation depend on it, in addition, almost all the current consumed by the motor flows through it, so it must be powerful enough. In our case, we made it composite, from two one-watt resistors.

The PCB of the regulator is 40 x 30 mm in size and looks like this:

The entire process of making and assembling a mini drill regulator takes about an hour.

After etching the board and cleaning the tracks from the protective coating (photoresist or toner, depending on the chosen method of manufacturing the board), it is necessary to drill holes in the board for components (pay attention to the dimensions of the leads of various elements).

It is recommended to drill holes from the side of the tracks, and in order to make the components easier to install, from the side of the parts, all holes must be slightly countersunk with a larger diameter drill (3-4 mm).

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Then the tracks and contact pads are covered with a flux, which is very convenient to do with a flux applicator, while SCF flux or a solution of rosin in alcohol is enough.

After tinning the board, we arrange and solder the components. Automatic speed controller for micro drill ready for use.

This device was tested with several types of motors, a pair of Chinese ones of different power, and a pair of domestic ones, the DPR and DPM series – with all types of motors, the regulator works correctly after adjusting with a variable resistor. An important condition is that it is in good condition, because poor contact of the brushes with the motor manifold can cause abnormal circuit behavior and jerky motor operation. It is advisable to install spark-suppressing capacitors on the motor and install a diode to protect the circuit from reverse current when the power is turned off.

Boron machines and drills

Mini drill Dremel 7000 Art 1.2.9

Two-speed drill Dremel (made in Germany) on AA batteries (4 pcs). Pre.

Mini drill Dremel 3000 Art 1.2.4

Dremel 3000 corded burr (made in Germany) is a convenient and proven tool.

Mini drill Proxxon 50 / E Art 1.2.8

Reliable mini drill Proxxon Micromot 50 / E from the German manufacturer Proxxon Micromot Syst.

Boers Art 1.2.11

Conical carbide drill bits for glass repair. Manufactured in the USA. Shank 1.6mm. Nakonechn.

Mini drill Dremel 200 Art 1.2.19

Corded mini drill 220V with speed switch (15,000 and 35,000 rpm). For more then.

Boers Art 1.2.12

Ball-shaped carbide drills for glass repair. Shank 1.6 mm. Working tip 1.2 mm.

Home Drill Rating

So, the rating of percussion “home” drills:

  • Metabo SBE 900 Impuls – very good drill with 900 W power, two-speed gearbox, speed control, keyless chuck and reversing.
  • Bosch GSB 21-2 RCT is a reversible model with speed control. Convenient to use, power can be adjusted.
  • Sparky BUR 150CET KL can be used as a wrench or screwdriver. There is overload protection and speed control.
  • Makita HP 2051 F – low power, but quite quiet operation, the presence of illumination of the drilling site and two speeds of work.
  • Bison MASTER DU-810 ERM2 is inexpensive, but with a very good package. Light in weight, easy to work with. There is a reverse and speed control. One speed mode.

Standard passport for an electric drill and its device

To understand how an electric drill works, you need to understand how it works. To do this, you can look at the technical data sheet of the device, where everything is clearly shown and painted..

Some features of the drill device:

  • Many models of drills have electronic speed control, which allows you to maintain the desired speed, even taking into account the load on the drill. Moreover, there are special torque devices that protect the motor from combustion if the drill suddenly becomes jammed..
  • Impact drills are renowned for their ability to work with particularly hard materials. A special percussion mechanism helps in this, which allows you to make hundreds of blows per second. True, for this, special drills are used, designed specifically for hammer drilling..
  • Trigger lock – the drills have a special button that can lock the trigger in case of long drilling. If you pull the trigger itself, the latch will release it.

By the way, the trigger itself is a switch that supplies power to the motor. In modern models, it is also equipped with a function for changing the rotation speed. With this trigger, the drill operation depends on the degree to which the trigger is pressed..

Recommendations: how to choose a drill for home

Before choosing a drill, you should decide which class of tool you need – household or professional. And then make the final choice of the device. For home use, a household unit will be enough, especially if you have to use a drill infrequently.

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When choosing a drill, keep in mind:

  • Power – home drills can range from 500W to 1,000W. This value makes it possible to work with metal, wood, concrete and other materials..
  • The presence or absence of an impact mechanism – for working at home, it is desirable that there was a “blow”, since often you have to perform a variety of work, where you need to check both walls and other very different materials.
  • Power supply – can be mains or rechargeable. At home, the first option is quite suitable. True, it’s better to stock up on an extension cord just in case.
  • Rotational speed – usually this figure is 500-1500 rpm. All drills have a dedicated rotational speed control knob, which should be used when working with different materials..
  • Hole diameter – these indicators can be found in the model passport. It is necessary to know the maximum diameters so as not to accidentally burn the tool on the very first working day..
  • Chuck Type – For home use, it is best to use a metal key chuck that holds the drill securely. True, in this case, you need to ensure that you do not lose the key to the cartridge itself..

If the work is to be done for a long time, the drilling machine must be periodically cooled by unplugging it from the network. It is especially necessary to do this if heat has gone from the drill body or the smell of burnt insulation has become audible..

By the way, the speed of rotation or the number of revolutions performed shows how the tool will behave when working with various materials. The higher this indicator, the higher the capabilities of the drill. Even if the power of the drill is small, the high rotational speed will override this. You can do a little test to make sure of this..

Analyzing all the points, we can say that a household impact drill with a power of 500-800 W with speed control and reverse is best suited for home..

Gear drill and other types of device

When choosing an electric drill, it is worth first of all to figure out what they are? Throughout its existence, this tool has received many varieties and was supplemented with a two-speed gearbox, reverse and other useful options..

There are six main types of drills:

  • Impact – With these impact tools, you can drill almost any material. Can work in 2 modes: simple drilling and hammer drilling.
  • Shockless – they are distinguished by the accuracy of drilling. Such an electric drill will perfectly cope with metal, plastic or wood..
  • Angular – such a unit has a rather narrow range of action, but it is this drill that is indispensable when working in a confined space.
  • Drill mixers – such a device is designed to mix different materials using a variety of attachments. You can mix adhesive solutions, varnishes, gypsum or cement mixtures, paints and other materials..
  • Screwdriver – drill – from the name it is clear that in addition to drilling, you can tighten various nuts and bolts with such a tool. The difference from other types of devices is the presence of a torque limiter or drilling depth.
  • Diamond drilling tools are professional drills capable of handling brick and reinforced concrete. There are “dry” and “wet”. The latter cope with hard materials, and the former with soft.

This is the main classification of drills. Its main mechanism is the motor, which generates the force to rotate the drill. But since the rotational speed of the motor itself is much higher than the rotational mode of the drill, the drills provide for interaction with the gearbox, which, if necessary, reduces the overestimated speed of the motor, and at the same time increases the rotational force on the drill. Such a geared drill is turned on, as a rule, with a trigger switch, which also controls the number of revolutions of the chuck.

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Homemade cordless rotary dremel tool/electric grinder(Adjustable speed) – diy制作12V锂电可调速手钻电磨

How to choose a drill with reverse and speed control

Electric drill with reversing and speed control

For mixing, drilling and screwing, it is better to purchase a universal tool with a high class of reliability. But if you just need a drill for a certain type of work, the best option would be to buy a device with this function..

DIY mini drill

The main use of the drill

  • drilling
  • engraving
  • grinding
  • milling
  • and so on, depends on the attachments used and imagination.


  • Collet allows to install drills and bits from 0.2 mm to 3 mm.
  • Supply voltage, 24.30 V.
  • Maximum current consumption at 30 V supply voltage and maximum current at maximum load on the motor shaft 0.6 A.
  • Maximum rotational speed 4500 rpm.

Principle of operation

Banggood – HILDA Orange 3.6V Mini Electric Cordless Battery Drill Variable Speed

When power is applied, the default is 50% power, the LED shines in yellow, using the S1 and S2 buttons, the speed is adjusted. 100% power, the LED is red, the minimum power that can be set is 20%, the LED is green. By the color of the LED, you can roughly control the power supplied to the engine. I will share my experience. When designing printed circuit boards, I set the diameter of the holes on the contact heels to 0.3 mm regardless of the diameter of the future hole. After etching the board, dots were etched in the place of future holes. There is no need for punching (punching) future holes. Let’s say an etched diameter of 1 mm, when drilling, the drill may shift and the hole will not be in the center of the contact pad.

Mini drill circuit

Description of the circuit

The VD1 diode protects the structure from incorrect connection. Smoothing capacitors C1 and C2. the controller is powered through a 7805L regulator. The motor is connected through a control transistor VT1. Resistors R1 and R2 limit the current through the LEDs. The S1- and S2 buttons adjust the PWM level. At the terminals PB1 and PB0 of the microcontroller, the S3 button is used to start the engine.

This circuit can be used, for example, to adjust the power of a low-voltage soldering iron by turning it on instead of the motor. Of course, the power level indicator is needed more informative than LEDs. But more on that later..

Photo mini drills

Construction details

The motor control circuit is assembled on two round boards, the tracks on them are cut with a cutter. The bottom board contains a microcontroller, a stabilizer, a capacitor C2 and a transistor. On the top, buttons S1. S2 resistors R1. R2 and LED. All elements are assembled in a cylindrical body, which is fixed on the back of the engine.

Microcontroller firmware

The program was written in the CodeVision environment, I programmed the microcontroller from the Algorithm Builder environment, I am posting a screenshot of the fuses installation from this program. The default values ​​of the fuses are set to “factory”, if the controller is new, then the fuses can not be flashed.