How to choose a polishing machine

Polishing is one of the most critical surface preparation processes: the flaws made during it will be noticeable at first glance. Therefore, the choice of a polishing machine should be approached with special attention, otherwise the tool will lead to one disappointment and will be unnecessarily gathering dust on the shelf.

Polishing features
Polishing is the last stage of surface preparation, all the mistakes of previous work on the polished part will become even more noticeable. There is no need to hope that the flaws will be “polished”, on the contrary – a poorly ground part during polishing will give out everything with reflection distortions and glare. In order for the polishing result to be pleasing, it is necessary to carefully prepare the surface with grinding machines – belt , vibration and eccentric .

The selection of a polishing machine also has its own characteristics – you need to take into account not only the features of the surfaces to be treated, but also your own experience. Polishing machines are an infrequent case when a professional model is better suited for a beginner: it is less likely to “screw up” the polish due to inexperience. Yes, a rotary model for 5,000 rubles can give excellent results even faster than a professional planetary model for 35,000, but only in the hands of an experienced craftsman. The saying “a cheapskate pays twice” fits perfectly with polishers.

Types of polishing machines
The differences between the types of polishing machines are noticeable at first glance: some look like large grinders, others like eccentric sanders. The similarity is not accidental.

Rotary polishers differ from grinders only in speed regulation and lower maximum rotation speed.

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Polishing is performed by rotating the disc, the performance of rotary machines is maximum, but the risk of damage to the paintwork is also the greatest in these machines. The disc, at an incorrect position, high load or too high speed, leaves circular traces of the “hologram” on the surface, which are clearly visible in bright light.

Eccentric ( orbital ) polishing machines are designed in the same way as eccentric sanders: the disc is not mounted directly on the motor axis, but is loosely fixed on the eccentric axis. During operation, the disc does not rotate, but makes small circular movements. The performance of these machines is low, but they also handle the surface more gently.

 

On the other hand, they are not very well suited for complex surfaces. The rotary machine can (only carefully) act on the surface at an angle, polishing the concave surfaces with the edge of the disc. But with an eccentric, it will not work out that way.

In planetary polishing machines, the disc is also fixed eccentrically, but not only vibrates, but also rotates. As a result, each point of the disk moves along a complex trajectory, reducing the likelihood of the appearance of “holograms” while maintaining high productivity.

 

Polishing Machine Features
Adjustment of revolutions
This parameter is not in vain included in the first place – the polishing machine must have an adjustment of revolutions. If the machine does not have this option, but you want to use a polishing tool, select the appropriate dimmer power .

The first stages of polishing are carried out at a minimum speed of 250-300 rpm. By the end of polishing, the speed increases with a simultaneous decrease in the load, but still it should not exceed 2500-3000 rpm. The values ​​are given for rotary and planetary machines, for eccentric machines it is more and more complicated: for them, the degree of impact on the surface no longer depends on the number of revolutions, but on the amplitude of oscillations, therefore, exact values ​​cannot be specified.The approximate dependence of the rotational speed on the eccentricity is given below.

Tip
Diameter The tip diameter affects the size of the parts that can be polished and productivity. The smaller the workpiece is, the smaller the circle should be. On the other hand, the larger the circle, the easier and faster it is to polish large surfaces. For fenders, arches and headlights of cars, it is better to use nozzles with a diameter of 100-125 mm.

 

Nozzles with a diameter of 150–180 mm are suitable for polishing large parts – hood, doors, roof.

 

Nozzles larger than 240 mm for polishing body parts are of little use and are used when processing other surfaces – large wooden and metal parts, door leaves, and so on.

Maximum number of revolutions
The parameter affects the performance of the machine: the higher the number of revolutions, the faster the polishing will be performed. But – up to a certain limit. When polishing paintwork with rotary and planetary machines, do not exceed 3000 rpm, otherwise the paint coating will start to overheat. When polishing stone and pure metal, the speeds can be higher – up to 4500 in some stages.

 

For eccentric machines, the rotational speed may be higher. Their maximum number of revolutions is strongly related to the vibration amplitude: the greater it is, the stronger the impact of the disk on the surface and the lower the maximum speed should be. For an eccentric polisher with low eccentricity (<3 mm), the maximum speed can be up to 14,000 rpm. For machines with a larger amplitude, it should be less – from 3000-3500 rpm.

Also keep in mind that low-cost machines will slow down under load.

Minimum speed
When polishing paintwork, the minimum speed is more important than the maximum. For rotary and planetary machines, a minimum number of revolutions of no more than 500 is desirable. If you have little experience with a polishing machine, it is better to choose a model with an even lower minimum number of revolutions – from 250. For eccentric machines, this parameter also depends on the eccentricity – from 1000 -2000 for machines with large eccentricity (> 3 mm) up to 3000-4000 for machines with large.

And also, in the absence of the option to maintain the speed under load, the minimum rotation speed in the real use of the machine may be several times lower than the passport one.

Maintaining constant RPM under load
An extremely important option, especially for craftsmen with little experience in polishing. Precise maintenance of the speed of rotation of the tooling at every stage is one of the conditions for high-quality polishing. Without this option, the rotation speed will “float” with the load.

The fastening of the
Velcro polishing attachments is safer and more convenient, the “skirt” with ties is cheaper.

 

If the sole of the tool is made of high quality, then there are no special differences in work, but professionals prefer Velcro – it is easier to change them, and during the polishing process this has to be done repeatedly.

Power Consumption
The power of the polishing machine must match the diameter of the disc. For attachments with a diameter of 125 mm for rotary machines, the power should be in the range of 800–1000 W, for 150 mm – 1000–1200 W and for 180 mm – 1200–1500 W. With less power under load, the revolutions will drop dramatically, with more power, the weight of the tool increases excessively.

Inrush current limitation
Another typical power tool parameter that is of particular importance to polishers. The fact is that the polishing machine starts up after it touches the polished surface, that is, under load. This is especially important for eccentric machines – at idle, their disk spins up strongly and when it touches the surface it can damage it. Therefore, the starting currents of polishers are higher than usual, which damages the engine. Limiting the starting current reduces the harmful load on the motor.

Power type
Under normal conditions, the best type of power supply for the polishing machine is from the mains. But, like other types of power tools, polishers have a cordless model.