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Overview of spindles for CNC milling machines

There are many types of motors that can be used as spindles for wood and metal milling machines. Many of them are quite specific and are manufactured specifically for machine models.

The review is designed for novice DIY makers to give a general understanding of the most commonly used spindles.

But if we talk about small-sized CNC milling machines, then they mainly use two types of motors, asynchronous (frequency-modulated) and collector. Each type of spindle has its advantages and disadvantages, let's look at ready-made examples.

Main types of spindles

The main types of spindles for small CNC milling machines are divided into:

• Collector, air—cooled - shaft speed from 0 to 35,000 rpm.
• Asynchronous air-cooled (controlled by a frequency—modulated power supply) - shaft speed from 0 to 24,000 rpm.
• Asynchronous water-cooled (controlled by a frequency—modulated power supply) - shaft speed from 0 to 24,000 rpm.

Collector spindles with air cooling

Collector spindles (in fact, they are Milling cutters, but they are used in CNC milling machines) are used in homemade and industrial machines (but mostly in homemade and small–sized ones), when the main task is to make the machine as simple and cheaper as possible. A lot of disadvantages of collector engines are covered by its ease of installation and low price (although not all models fit the low price parameter). It is difficult to single out the main drawback, because they are all very unpleasant. Collector spindles, due to the presence of brushes, make very loud noise during operation, the shaft speed may vary, which often depends on the load (as well as on the input mains voltage). This makes it difficult to accurately set the desired milling modes, as a result, they always leave a margin in a smaller direction (that is, for the sake of a margin for a non-constant speed, there is an increased processing time of the product).

"Collectors" require regular maintenance, long-term operation of the spindle requires frequent replacement of brushes. If you change the brushes in the drill every 2-3 years, with moderate use, then in the machine you will have to do it every 2-3 months, if not more often. Collector brushes emit strong electromagnetic interference, and erased brushes can spark strongly, which can become a source of accidental ignition (at least collector motors cannot be left unattended for a long time). Collector spindles are installed because of their low cost and ease of connection. In addition to erasing the brushes, the collector halyard itself with contact plates is also erased. With significant wear, the collector must either be changed or put another spindle (milling cutter).

Below are the most common collector models of milling cutters (for spindles) from 50 W to 800 W:

A milling cutter (a drill, or an engraver is also often used in small-sized milling machines).

• Proxxon milling machine from 50 to 120 W (depends on the model), at 5000-20000 rpm.
• Prices from 1000 to 2500 rubles (models are presented just for review).

Other milling machines (dremel, drills, engravers, all somehow "Buzz").

The basic rule is simplicity of connection, built—in speed control and the same speed from 500 to 30,000 rpm.

The price of such babies is from 900 to 3000 rubles (we are considering Chinese models).

The main disadvantage of all collector cutters is the large noise produced during operation. Of the advantages, we can note a small weight (although this does not particularly affect the spindles for the machine).

• Kress 800 FME milling cutter, 800 W, 10,000-29,000 rpm
• The price is about 11,000-12,000 rubles.
• Chinese analogues will cost 2 times cheaper.

Let's take for example more "massive" models that have almost the same characteristics as those listed above.

The GKF 600 W 33000 rpm milling cutter, although this model can not be called cheap, since its price is about 13,000 rubles.

It is worth considering, of course, that the lower the power of the milling cutter, the less performance it will have.

And naturally, if we consider the Chinese analogues of some models, then a perfectly acceptable price will rest on 3-4.000 rubles for 600-800 watts.

• This Chinese baby will cost only 3,500 rubles, at 800 watts and 30,000 rpm.

Asynchronous air-cooled spindles (collector and brushless)

In CNC machines, such spindles are used complete with an inverter – a device that converts 1 phase of 220 volts into 3 phases of 200 volts, and converts the 50 hertz network frequency to a higher one, which the inverter regulates at the output. As a rule, the adjustment range is from 0 (the first frequency threshold can be 100 Gr)up to 400 hertz, and this allows you to control the spindle speed using a frequency ranging from 0 (3,000) to 24,000 revolutions per minute. The inverter allows you to achieve a stable rotation speed regardless of the load on the cutter, and almost constant power on the shaft regardless of the rotation speed. These spindles do not have wearable brushes, which allows them to be used for years without maintenance. The disadvantages include the dependence of the spindle temperature on the ambient air temperature, significant heating of the spindle housing, and the "buzzing" of the air cooling impeller, which at high speeds can cause whistling. In addition, when using such a spindle with the aspiration system turned off (chip pump), the flow from the cooling fan of the spindle can greatly inflate the chips around the room. But, due to the lack of need for the supply and circulation of coolant (as it is done on water-cooled spindles), it often becomes the reason for choosing just such a design.

The disadvantages of brushless asynchronous spindles, both air-cooled and water-cooled, include their high price, plus, it is worth considering an additional inverter with a power supply). But still there are more positive characteristics:

• Low noise level.
• Low vibration level.
• Long-term uninterrupted operation.
• High torque on the shaft.
• Maintaining constant speed at different loads.
•  

The disadvantages of collector asynchronous spindles include several points:

• Wearability of brushes (300-500 hours of operation).
• Wear of collector copper plates (~1000 hours).
• *The wear time is indicated based on examples, although it all depends on the manufacturer, and may differ by 1.5-2 times.

Asynchronous air-cooled spindles are produced in fact for milling machines, that is, they are not used in other areas.

The bulk is made in China, hundreds of sellers can be found on Aliexpress, but there are only about a couple dozen models.

Air spindles are produced mainly up to 800 watts, although there are models of 1.5 kW, although they are used less often (they can get very warm, plus the high speed of the cooling fan will create unpleasant noise at speeds above 12,000).

Although they are structurally simpler and easy to operate, therefore, air-cooled models are also available for sale at 800 watts and 1.5 kW.

Basically, we can note four models of spindles for 200, 300, 400 and 500 watts, which have the same characteristics in size, the difference is only in length.

• 200 W 3000-12000 rpm, torque 230 Nm/m.
• The price on Aliexpress is from 1200 to 1600 rubles.
• Low-power models also have brushless and collector models.
• *Excluding mounting and power supply!

• 500 W 0-12000 rpm, torque 500 Nm/m.
• The price on Aliexpress is from 1800 to 2500 rubles.
• There are collector, there are brushless.
• *Excluding mounting and power supply!

All spindles in this category have the same diameter - standard 52 mm, which simplifies their use in milling small-sized machines for wood and metal. And they differ only in length.

The spindles are equipped with an ER11 or ER16 collet clamp, a standard drill chuck can also be used. Small-sized models come mainly with an ER11 collet.

The model of the puller for the collet can be viewed here.

Almost all spindles from this line have a thickness of 52 mm, so their installation is included in a certain template.

Since it will not be possible to increase the length indefinitely to increase the spindle power, air asynchronous spindles at 800 W and above have a different diameter.

Models from 800 W and above have a diameter of 62 mm and above.

How to distinguish a collector spindle from a brushless one

(Description and title added to article 10.08.2021)

Since most sellers on Aliexpress do NOT indicate in the parameters of collector spindles that it is collector (yes, it is) — an uninformed buyer will understand this only after the spindle starts working intermittently ...

(Based on my own experience).

So, everything is quite simple:

Collector spindles have one power supply and are produced mainly up to 800 watts (although this is not an indicator). But basically most of the inexpensive 200-400 Watt models come with a collector (brush) design.

Brushless spindles have an inverter and a power supply (although there are models with a one-piece unit that includes an inverter and a power supply in one box).

Examples in pictures:

Collector (brush) with a simple power supply, with parameters of 48 Volts and a current frequency of 400 Hz:

Below are Collectorless spindles.

*The inverter in this design serves as the main working condition. Unlike collector-brush motors, here the collector (rotor) itself consists of a flywheel with magnets, and windings are located on the stator. Due to the operation of the inverter, a shift of the electromagnetic field in the coils is created. the rotor magnets seem to be tightened by a constantly shifting electromagnetic field, thus creating rotation. (This is a simple explanation for general understanding...).

As you can see from the pictures, the brushless spindles have a separate inverter and a separate power supply.
Beskolektorniki at 800 watts and above have a speed of up to 22,000 and structurally have Four bearings (at least this should be paid attention to).

They are 30-40% more expensive than collector models. The price is higher partly due to the presence of an inverter unit, and technologically they are somewhat different. Let's say a collector for 500 watts with a power supply will cost about 6,000 rubles, the same collector for about 8,000 rubles (the price is for a set with power supplies).

Pay attention to the execution when buying, as I have already written, sellers often do NOT indicate that the spindle is with brushes, that is, collector. It is understandable, the service life of such a motor before repair (at least replacement of brushes) will be from 300 to 1000 hours, that is, wear on the seller's hand, since there will always be new sales... Although brushless motors are not eternal, it is also worth understanding.

By the way, the cost of the peripheral, that is, the power supply and the inverter cost about 40% of the total cost of the spindle. Therefore, let's say the set costs 10,000 rubles (500 W spindle with inverter and power supply + delivery) and the spindle itself costs only 4500. Therefore, if one of the components fails, the replacement cost will be lower than the total set. It is also worth asking the seller if he will not put an additional engine in the kit separately, well, as an option. Let's say my machine works 20 hours a day, 6 days a week, and when something goes out of order, it's easy to be expensive, and it's sometimes expensive to wait for components from the store.

Asynchronous (brushless) water-cooled spindles

Asynchronous water-cooled spindles have the same data as air-cooled ones, but they also have their undeniable advantages:

The absence of an impeller makes such a spindle virtually silent (the water pump usually works very quietly). The noise from such a machine usually comes from a milling cutter and from stepper motors.

Water cooling maintains a low temperature of the engine itself, which has a positive effect on the long-term operation of the built-in bearings.

Also, most of the spindles with "dropsy" have a speed from 0 to 22-24.000 rpm. Which in the case of air cooling will create a high noise level.

Of course there are disadvantages — this is the need to equip the system with cooling hoses, a water tank and a water pump. It is also worth considering that the water in the tank will still warm up and it needs to be replaced periodically. In the cooling system, it is recommended to use not plain water, but antifreeze — which reduces the formation of scale, and prevents the appearance of algae in the water.

• Asynchronous spindle with water cooling at 800 W and 0-24.000 rpm.
• Price on Aliexpress 8.500-9.500 rub.
• *The cost of the Inverter, power supply and pump is not taken into account!

The disadvantages of asynchronous spindles, both air-cooled and water-cooled, include their high price. Although, judging by the prices on Aliexpress, the cost of 500-800 W spindles is even lower than some expensive collector analogues.

In small-sized machines, home-made workers often use boreholes, dremels, drills, and similar milling tools, sometimes fixed even with simple nylon ties... Although the needlewomen are still maniacs :)

If the CNC is used in high-precision jewelry work, then sometimes high-speed spindles with a shaft frequency of up to 60,000 rpm are used. But all of them can be attributed to the category of special equipment and are not usually used by crazy pens.

And here is an example of crazy pens. Although it is worth paying tribute, obviously the owner of the "crazy pens" is only 15-16 years old and this is commendable for such work. Of course, the accuracy of such a machine is practically nonexistent — but to get acquainted with the technology of milling using CNC is quite acceptable and commendable.