The rotary is often considered to be the adversary of the Dual Action polisher. It is a polishing machine that uses only 1 type of motion to create a polishing effect. It is very good at cutting, works quicker then a DA, but also requires much more experience and knowledge to use properly. Many consider the rotary a medior or senior level of experience machine.
Why use a rotary
A rotary offers greater cutting speed, which is very handy when you are either short in time, need to achieve much result on a large surface or have a very badly damaged surface to correct. However, this comes with a price. The increased cutting power makes it easier to cut more then is needed. If you are un-experienced with a rotary, it is easy to polish away more paint then is needed, increasing the risk of burning through the paintwork. This is a very costly mistake to correct. The rotary doesn’t have a forced or free rotation movement, such as the DA. Eliminating the risk of making the machine stop moving. This can sometimes be useful in small spaces. Because the machine doesn’t have any “throw”, it can be more easy to work very close to an edge or sharp corner.
Differences between rotary’s
There are no very significant difference between rotary’s other then the most common difference between similar machines:
- Power (wattage)
- Type of variable speed
- Gentle start (starts slow regardless of the speed setting, then quickly revs up to the set speed)
- Minimum or maximum speed
- Type and/or size of backing plate
Danger of a rotary
A rotary only spins around its axle, it doesn’t have any secondary motion. This means that polish pad just spins around, similar to an angle grinder. When turning at high speed, the top of the pad (farthest away from you) is spinning to the right (clockwise) which means the bottom of the pad (closest to you) is spinning to the left. If the pad is hold perfectly flat on the surface, these cancel each other out and your polisher stays where it is. However, if you change the angle to the surface, and the top of the pad has more friction with the surface then the bottom of the pad, the polisher will “pull” to the right. If the angle is changed so that the bottom of the pad has more friction, the polisher will “pull” to the left. The same goes for changing the angle to the left or right. A body panel is rarely perfectly flat and straight, meaning you need to move with the surface of the panel or the polisher will “walk” on its own: pulling in various directions. This behaviour is sometimes referred to as “walking”.
Burn through paint
A rotary can often turn at higher speeds then a Dual Action polisher, it can also withstand higher pressure. These 2 factors make it very useful for cutting. But when these factor are overdone, you can cut more and faster then expected, meaning you could polish/cut off an entire layer of paint. Removing the clear coat is called a “strike through”, removing the complete colored coat (showing the primer underneath) is called a “burn through”. Both of these faults are very difficult with a Dual Action polisher, but more likely to happen when using a rotary polisher. Especially if the user is not very experienced.
The speed at which a polishing pad moves, can be fairly quick. And the size of the pad makes it even more dangerous. Lets say that a polisher rotates at 4000 RPM. The polishing pad in this example is a 6″ foam pad. This means that the pad has a diameter of 6″ and rotates 4000 times per minute. The pad is 6″, which equates to 18.8 inch in circumference. It spins 4000 times a minute, meaning it travels 4000 x 18.8 = 75.200 inches per minute (almost 1.2 miles per minute). This equates eventually to 68.7 miles per hour. If you hit something with the edge of your polishing pad, you are rubbing against it with a speed of 68.7 miles per hour. It is very easy to cause serious damage at this speed.
Users of a rotary, especially the inexperienced ones, will often wonder why they finish with marks that look like a very fine mist of marks. It almost looks like there is an oily substance breaking the light on the surface, with no clearly visible scratches. These are holograms, or buffertrails. A very common sight after using a rotary polisher. This is often the result of not letting the polish degrade well enough during polishing. It can also be cause by moving to quick, using a high speed setting or not enough polish product on the pad. Normally, these holograms are easily removable by following up with a dual action polisher and a finishing polish. It is tricky to achieve a perfect finish with a rotary, but it is possible.
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