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 How To Polish Paint Part IV: Machine Polishing

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jjski78
The Engine Guy
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Posts : 172
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Join date : 2009-02-10
Age : 39
Location : Austin, AR

PostSubject: How To Polish Paint Part IV: Machine Polishing   Sun Mar 01, 2009 9:50 pm

Machine Polishing (car polisher)

Most professional detailers use rotary buffers and dual-action polishers to polish paint. The overwhelming reason is time. To do the job properly by any other method would take too much time.

There are basically two kinds of polishing machines: rotary buffers and dual-action (orbital) polishers. A professional rotary buffer is little more than a body grinder with a polishing pad in place of the grinding disc. These are high-power, variable-speed motors that give a professional painter or detailer a lot of flexibility. Rotary buffers have a straight drive to the polishing head (i.e., the polishing pad connects directly to the shaft of the motor), whereas dual-action polishers have a special drive head that causes the polishing disk to run in an orbital pattern while also rotating.

I often get questions like "Who should use a rotary buffer and why?" or "What's better, a dual-action polisher or a buffer?" This is not an easy question, because no matter what I say, there is an opposing and equally valid response.



This is the Porter Cable random-orbit polisher. This is a great machine, but not perfect. A good upgrade is a 6" Velcro backing plate and Velcro-backed pads. This is the first random-orbit polisher I've used that has enough power to satisfy the most demanding professionals.

Rotary buffers are for trained professionals and serious enthusiasts with experience. The possibility of ruining a paint job with a rotary buffer is very high when a powerful, rotating machine is put in the hands of an unskilled person. Rotary buffers spin at speeds up to 3600 rpm. One small slip, and you'll pop off a molding, burn a hole in your paint, or break off a windshield wiper. I've seen each of these mishaps, so I know it can happen. That said, the rotary buffer is my tool of choice. I put myself in the category of a serious enthusiast with lots of experience, and I have had two minor mishaps in 20 years. For me the result is worth the small risk.

A good dual-action polisher can also deliver great results on all but the worst paint finishes. For this reason alone, I think most enthusiasts and novice detailers should invest in a dual-action polisher, not a rotary buffer. Polishing machines can be purchased for as little as $50 or as much as $300. The difference in capability is significant. At the low end are low-power orbital polishers. These machines are designed for the average car owner who wants an easier way to polish and wax his or her car. Although they will make the job of polishing and waxing easier, they will not improve the resulting finish of your car. At the high end you will find multipurpose detailing machines, like the Porter Cable 7424, that polish and buff.

Car Buffing & Polishing Pads

There are two basic pad types: cutting and polishing. A cutting pad is used with a polish or machine cleaning compound to remove oxidation and fine scratches. Cutting pads make quick work, but will leave noticeable swirl marks, especially on dark finishes. After buffing with a cutting pad, you will need to make a second pass with a polishing pad and glaze to remove swirl marks and improve luster. Cutting pads, also called leveling pads, should be wool. There are a lot of synthetic "wool" pads on the market. Don't touch them! Nothing beats lamb's wool. Nothing is safer than lamb's wool. Polishing pads, often called finishing or waxing pads, are foam rubber. These are the only pads safe to use on a clearcoat finish. Do not use a cutting pad on a clearcoat finish. That said, some expert body shops will use a cutting pad on a clearcoat finish when blending a repair.

Compounds, Polishes & Glazes

Always use the least abrasive polish necessary to get the job done. No matter what you might have read or seen on TV, no single polish can do it all. You may need two, even three products to get the desired results. Any polish you use with a buffer or rotary polisher should state "for machine use" in the instructions. I know I've said it before, but I feel it's worth repeating: Be very careful using a rubbing compound with a machine.

A rubbing compound is nothing more than sandpaper in liquid form. If your paint needs light compounding, it's best to do it by hand. If you must use a buffer or rotary polisher, compound flat areas only and stay away from edges. Next up from rubbing compounds are paint cleaners. Paint cleaners are basically a fine cut compound for polishing paint with heavy or moderate oxidation. Paint cleaner polishes will quickly remove the top layer of dead paint, revealing paint that can be rejuvenated.

Polishes are the paint finish workhorse. Unlike rubbing compounds and cleaners, a polish has very little cutting action. A good machine polish will remove small blemishes and restore gloss. A quality polish contains oils to lubricate paint surface for the best polishing action and a high-gloss finish.

Preventing Car Polisher Paint Burns

Buffing or burning through your car's paint is perhaps the greatest danger in using a machine. The risk of paint damage can be largely diminished if you follow a few simple rules. A paint burn is caused by heat buildup on the buffing pad due to friction. Paint burning occurs on the edges of a body panel, not in the middle. I cannot recall seeing a buffer burn though paint in the middle of a hood, door or fender. It is the small surface area of the buffing pad edge that builds heat quickly, making a burn possible.

To prevent burns, you need to know how the rotary buffer works. With few exceptions, buffers rotate clockwise. When using a buffer, lift the left side of the buffer slightly (a half inch or so). Move the buffer in smooth left to right strokes. It is best to focus pad contact on the 12 o'clock to the 4 o'clock quadrant (i.e., the right edge when looking at the top of the buffer). In this way, the buffing pad will always rotate off the edge of a panel. The reason for lifting the left side of the buffer is to prevent the trailing edge of the buffing pad from driving into a body panel edge. The trailing edge of the pad driving into a body edge creates so much friction it can rapidly burn through the finish. By rolling the right side of the pad off the body panel edge and lifting the left side, you can significantly reduce the risk of burning.

To further reduce the risk of burning, buff up to edges and body ridges, not on them. When buffing raised peaks or body lines, keep the buffing pad as flat as possible, and slow the buffer speed. Keep the buffing machine moving at all times. If you allow the buffing pad to spin in one spot for more than a few seconds, you're inviting disaster. Other tricks include opening the door, trunk or hood slightly. This gives you an edge to roll off of when buffing.

Always slow buffer speed when approaching an edge. The operating speed of your buffer is very important. I highly recommend using slower speeds. Speeds between 500 and 750 rpm are sufficient on most modern finishes. The slower speeds can also be used on older finishes to achieve good results. Just remember, slower speeds create less friction, thereby reducing the chance of burns.

Car Polisher Techniques

Safety first. Wear goggles or work glasses when buffing. Remove all hand and wrist jewelry. Just like polishing and waxing by hand, buff a section at a time.

Always start with the least abrasive polish you can. Polish a section more than once if the results are not satisfactory. If you are not getting the result you want, try a slightly more abrasive polish. Like I said, it is unlikely that a single polish will do it all. For example, the front of your car gets the most damage. It may require a medium-grit polish to bring the front areas up to par, while the remainder of the car buffs up fine with a mild polish. To properly machine polish, you will need your polish in a squeeze bottle. Squeeze a couple of lines (6 to 9 inches) of polish on the panel you want to polish.

Pre-lubricate your buffing pad with a shot or two of water or detailing spray. Start the machine slowly, with the pad on the panel to the right of the lines of polish. Lift the left side of the pad slightly, and slowly move into the polish. The rotating pad will pull the polish in and begin distributing it on the paint.

If you're new to machine polishing, apply your polish to the buffing pad, not the surface of the car.

If you're brand new to machine polishing, don't worry. Start learning by applying a single line of polish around the edge of the buffing pad (as shown above). Don't use too much polish, or it will splatter everywhere and take too long to buff out. The amount I have applied here will be enough to buff a complete fender on a small car.

Before starting the polisher or rotary buffer, lay the pad on the paint surface to be worked and spread the polish around. Once the polish is distributed over the area you're working on, you can begin to increase speed a bit. If you're using a rotary buffer, do not run above 1500 to 1800 rpm. If you're using a Porter Cable 7424 dual-action buffer, there's no reason to run the machine higher than 4.5. Work the polish in well, using overlapping left-to-right and top-to-bottom passes. There's no need to rush, but remember to keep the pad moving.

As the polish begins to "buff out," and the shine on the paint begins to come up, the polish and buffer have done their work. Don't keep buffing the dry panel. It's no longer productive, and you risk burning the paint. If you're not happy with the results, add more polish and keep going. Remember to stay off the edges! When working on top panels like the hood, trunk or top, you can keep the electrical cord from rubbing on your freshly polished paint by draping it over your shoulder. It's also best to remove your belt or anything else you might be wearing that would damage your paint.

Be sure to check your buffing pad periodically, as it will become caked with polish. Use a pad spur to clean it. Lay the buffer across the top of your leg and turn the machine on. Gently press the pad spur into the pad, starting at the outer edge, and run it into the center. Foam pads can be cleaned with soap and water for end-of-day cleanup. Allow pads to drip dry. Machine polishing is messy. The polish will fling off about 6 feet or so. You can prevent the splatter mess on your car by using an old sheet. Simply cover the area of the car you're not working on. Cover the things in your garage you don't want splattered, too.

CAR POLISHING SUMMARY

Polishing paint is a acquired skill. It can take years to master. If you're planning to use a machine, my best advice is to practice on older cars. Most importantly, select the correct polish for the job. Use the chart at the beginning of the chapter to help determine which polish grade you should be using. Once you've selected the right polish, make sure you use the right tools.
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