Common, 'free-rotation' DA's use an electric motor (Running through a right angle gear drive to multiply torque and reduce speed.) which rotates an offset crank with a freewheeling bearing hub on one end and a suitable counterweight on the other. The backing plate shaft is screwed into the offset freewheeling hub, which allows the pad to follow a controlled circular orbit whilst simultaneously rotating at an independent speed determined by the friction and gyroscopic forces on the pad. This motion is referred to as a 'random orbit'. These two separate planes of movement can be measured in the following fashion: Orbit Length, OPM, and RPM.
Orbit Length is determined by how far the freewheeling hub is offset from the physical center of the crank, and controls the ultimate distance traveled by the pad in any given crank rotation. Garden-variety DAS-6 & G220 model DA's have an 8mm orbit length; Rupes models and their copies typically vary between 12-21mm.
OPM stands for Orbits/Oscillations Per Minute, which on these machines is a factor of the RPM of the motor, and changes linearly with the variable speed of the motor. To increase pad OPM's, increase the speed of the motor.
RPM stands for Rotations Per Minute, which on a 'free-rotation' DA is a factor of the gyroscopic forces and friction placed on the pad/backing plate and its bearing hub. To increase pad RPM's, decrease pressure whilst maintaining or increasing the motor RPM's.
One can vary the pad RPM's & OPM's to one's advantage by manipulating motor speed and downward pressure on the machine. Here is a further explanation of some of the physics involved:
http://www.buffdaddy.com/files/1519584/uploaded/KBM-Kevin%20Brown%20Method-Machine%20Stroke%20-%20How%20It%20Affects%20Sanding%20and%20Polishing%20Performance.pdf.
As for the Zenith-Point-Method, this technique was popularized by DaveKG, and is very helpful with achieving the best results whilst using traditional Diminishing Abrasive Polishes like Menzerna, 3M, Dodo-Juice Lime Prime, etc. These polishes feature abrasives which start off at 'X'-Size, and end up at a finer grade (Say, P2500 initial starting grade, to P5000 final finishing grade.) due to friction, with a fairly linear decrease throughout their working cycle.
I equate the ZPM to being like slowly warming up the tyres on a racing car to increase grip, allowing you to go faster once the rubber has reached operating temperature, and then making a few slow 'cool down' laps to bring the temperatures down without heat-cycling and damaging the engine/brakes/tyres. One starts off at speed 1 (1800-2500 OPM's) and slowly increases speed with each pass to slowly work some heat into the lubricants until reaching your full operating speed (Around 5800-6000 OPM's at speed 5), which makes them more fluid and gives the polish a longer working time, before slowly decreasing speed again to play the product out and prevent it drying up. This allows you to make the most out of the abrasives, and ensure that they are fully diminished by the end of their cycle for maximum gloss and defect removal.
This, along with the Kevin Brown Method for non-diminishing polishes:
http://www.detailingworld.co.uk/forum/showthread.php?t=289564, are the core techniques for machine polisher usage. All advanced techniques build on these two methodologies, which is why it is important to practice them, and develop a foundation of understanding. If you encounter a situation requiring a correctional extreme (Either finishing soft paint, or removing stubborn defects from hard paint; two processes at the opposite ends of the machine polishing scale.), what these techniques can teach you is crucial.
Hopefully this helps... If you have any more questions, please feel free to ask. :thumb:
- Steampunk