The D A (dual or double action) polisher has undoubtedly become one of the most useful labour saving devices in the vehicle bodywork professional's armoury. Along with the compressed air spray gun, it is almost irreplaceable. What it does, and how to use it, aren't black arts however. Here is a guide to the DA polisher.
How it works
Polishers come in three types and are electrical or air driven tools to assist in either finishing paintwork (normally automobile) or making it shine. The first type is the orbital. This is a single action design wherein the polishing head simply oscillates (often at a fixed speed) in order to spread a chosen polish or wax quickly. This type of unit will bring out the shine but won't remove paint defects. The second is the rotary unit. These are single action polishing machines on which the head simply spins on a directly driven spindle. The speed is adjustable but they are difficult to use and more suited to paint removal. Use in defect rectification can lead to over cutting with too many layers of paint being removed. The last type is the dual action tool. This works by combining the operations of the previous two. The polishing head spins on its axis and oscillates at the same time. Coupled with adjustable rotation speed, this makes them easy to use as both defect rectifiers and polishers. The benefit of using DA is that it doesn't centre the action of the tool on the work, so swirl marks are easier to avoid. They can also be used quite successfully with sanding attachments to flat paint back during the early stages of the paint spraying process.
How to use them
The method of operation for a DA tool is basically the same for all its uses, just with different products. To use it as a flatting device, you need to attach a sanding plate. Using wet or dry paper, you apply the machine lightly to the wet panel and work it round gently. Repeat this using steadily finer grades of paper until the surface feels smooth. In its role as a paint finisher you need to fit a cutting pad. Apply your cutting compound to the pad and spread it onto the panel before switching on the machine. With the pad on the work, switch on (low speed first) and move it around the panel. When the pad is dry, buff the work with a cloth and repeat if necessary. Use as a wax finisher is much the same but needs a mop head instead. There are many of these to choose from but the trade favour Porter Cable and Meguiars polishers.