Polish Makes Perfect

Many moons ago, as a Boy Scout in Montana, we told a story around the campfire about how to catch a raccoon: you’d anchor a clear bottle to the ground and put some crumpled tin foil inside. A passing raccoon (there’s always a raccoon passing by) would be transfixed by the glint of the foil and reach in and grab it. But in making a fist around his shiny prize, he’d be prevented from removing his paw. I guess we thought the raccoon would be too dumb to just let go and free himself.

Polished airplanes are few, and there’s a good reason for that: it takes a lot of elbow grease to bring a mill finish or corroded skin to a mirror finish, and once there, it takes even more elbow grease to keep it that way. Shiny planes magically attract much more dust, bugs, and fingerprints than a painted plane. Sometimes a well-intentioned culprit tries to rub off their prints with a shirttail and merely succeeds in leaving a fine haze of swirly scratch marks. A polished plane will try your patience.

So consider yourself warned: The initial polish is likely to require 50–100 hours depending on the size of the plane and condition of the aluminum. And to keep it mirror-finish, you’ll need to repolish at least once, if not twice, a year, depending on the weather it’s exposed to (although repolishing only takes a few hours, assuming you did a good job on the initial polish). Once done though, you’ll have a plane that’s pure eye candy.

Tools of the Trade

This article will describe polishing using Nuvite brand polishes. While other brands are available, Nuvite polishes are the most popular among aircraft owners. Before polishing your plane, you’ll need to assemble the following items:

• Variable-speed compound rotary polisher & pads: Also known as a compunder, both the Dewalt DWP849X and Makita 9227CX3 are good units and get great reviews. Get electric, not pneumatic; otherwise your compressor will be running constantly. Likewise, avoid drill-mounted buffers, except for areas that are too small or delicate for the compounders listed above. The compounder requires a 7.5-inch wool compounding pad (and a pad cleaning spur). Stick with wool; cotton and synthetic don’t work as well. Get one pad for each grade of polish you plan to compound with. (Note: I’ve not had good luck with the Makita backing plates, which tend to break at the neck after a few hours of use. If you purchase a Makita or a unit with similar backing plate, I’d strongly recommend switching these out for stronger aftermarket plates [see photo on page 25]).

• Dual head random orbit polisher: Don’t mess around, cry once and get the Cyclo Model 5. It’s expensive, but worth it. You can usually find like-new units on eBay for half the price of retail. If you buy used, be sure to ask the seller to include any accessories (such as pads or polish) they might have collected.

• Nuvite polish: The various grades are explained in Table 1. Nuvite keeps well if the lid is properly screwed on, so if someone offers you an old jar, give it a shot (just be sure to stir well first, as the polish can separate out from the carrier). Begin with one pound each of F7 and S. This will probably be more than adequate for a Sonex-sized plane, and not quite enough for an RV, but it’s a good place to start. You may want a quarter-pound of F9 and/or C as well—see the polish chart below.

• Fleece wraps: These wrap around the Cyclo pads. Begin with a 20-pack for a small plane, 30 for a larger plane (more if you don’t plan to wash and re-use).

• Microfiber towel: 12-pack for a small plane, 18 for a larger plane.

• 1 gallon mineral spirits: Lacquer thinner works fine.

• 16 oz. box corn starch: one box for small plane, two for a larger plane.

• 16 oz. tub of TSP (trisodium phosphate): Compounder pad cleaner.

I sourced my consumables (polish, wool pads, fleece wraps and microfiber towels) from Tom Numelin at Perfect Polish. Numelin’s customer service is top notch and his prices were the best I found (and free shipping!). His web site (www.perfectpolish.com) contains a wealth of information, and he includes an excellent guide to aircraft polishing with his shipments.

Expect to pay between $400–$800 for all tools and consumables listed in this article. The low end assumes you are a good scrounger and are able to find a used Cyclo and some unused polish on eBay or from another builder. The high end assumes all new products.

A Method to the Madness

Similar to most polishing methods, we begin with a course polish and work our way up to a fine polish, removing scratches and oxidation along the way. You’ll perform your initial passes with the compounder to do the brunt of the work, then follow up with Cyclo passes to remove the fine-line compounder scratches in preparation for the subsequent grade of polish. Nuvite polish ratings are shown in Table 1.

Polishing invites experimentation: after several hours of polishing, you’ll naturally start to wonder if you can’t move things along a little faster if you use, say, G6 instead of F7, or if compounding with C is really necessary. The ability to polish one section of wing, and then try another method immediately adjacent and compare results, makes these experiments fun and worthwhile. Nevertheless, as a starting point, the following is what I’ve found to get me fastest from mill finish to mirror finish (note that this schedule is for Alclad aluminum; non-alclad skins like 6061 may require a more aggressive schedule):

1. [OPTIONAL] 2-3 passes F9 with the compounder (if starting with corroded or scratched aluminum; F9 Cyclo unnecessary if following with F7)
2. 7–10 passes F7 with the compounder
3. 2–3 passes F7 with the Cyclo (discolored or hazy areas may require additional Cyclo passes)
4. [OPTIONAL: 2–3 passes C with the compounder]
5. [OPTIONAL: 1–2 passes C with the Cyclo]
6. 2 passes S with the Cyclo
7. 1 pass clean fleece with the Cyclo
8. Corn starch and microfiber rub-down

Experience Teaches…

Before starting with F7 or F9, thoroughly clean the surface to be polished with mineral spirits and a microfiber cloth. It’s important to remember to repeat this step between each grade of polish so that a courser grade of polish (left behind in rivet heads, butt seams, etc.) does not contaminate the subsequent finer grade. I’d suggest starting on the (right-side up) underside of the horizontal tail to perfect your technique before moving to more visible surfaces.

Note: I do not recommend waiting until the airplane is fully assembled to begin polishing. Polishing is physically strenuous and in my experience, the more pressure you put behind the pad at the F7 stage, the quicker the metal reforms. You can produce this pressure with your back, or with gravity; give yourself the advantage by polishing individual parts before assembly on a workbench or low table where you can put your weight behind the compounder rather than using your back. This goes double for lower surfaces (bottom of the wing, fuse, and tail). Note also that thinner sheet aluminum (.016, .020) doesn’t polish up as easily or quickly as heavier gauges (.032, .040), since it flexes more under the pressure of the pad, counteracting the reforming process. So, expect control surfaces to take a bit longer.

Begin by dabbing a four-foot grid of M&M-size blobs of polish every six inches or so and compounding with F7 or G6 (I haven’t noticed a significant difference in the two, other than that F7 seems to hold its bite a bit longer). Torque—not rpm—moves the metal. Keep the speed low: 600 rpm for the initial pass spreads the polish out nicely without flinging it to far corners of the workshop, then 900–1200 rpm as you work out the polish. Hold the pad at about a 15° angle to the metal.

Move in parallel unidirectional sweeps across the metal (it doesn’t seem to matter if you move parallel or perpendicular to the mill grain); don’t bop around as if you were buffing out a car. Move the compounder as slowly as possible without overheating the metal beneath—typically about one to two inches per second. Make sure the pad is rotating away from any sharp or loose edges. Catching an edge will bend up metal in the blink of an eye.

Heal and Reform

Done properly, the compounder passes with F7 will actually bring the mill finish to a medium-grade mirror finish. This first stage takes 80% of the time and is where most of the hard work is done. It sets the stage for both the final quality of your finish and how much you’ll need to repolish in the future. The F7 heals the mill finish and blends out minor scratches, but does leave a fine pattern of swirl marks on the metal. (Heal and reform are the words used by polishers to refer to modifying the surface of the aluminum in such a way as to achieve a mirror finish; the base metal is not removed, but rather undergoes a plastic reformation.)

The next step is to remove the swirl marks with the Cyclo using the same grade polish. The Cyclo itself does little to heal the metal, so make sure the metal is in the condition you want it before moving to the Cyclo. Polish is again dabbed on at six-inch intervals over about four square feet, although more sparingly compared to the amount used for compounding. Run the Cyclo in horizontal, then vertical sweeps—you should have a fairly uniform blackened surface after your first pass, but the fleece will quickly pick up the polish, leaving you with a nice mirror finish. It’s not uncommon to have areas of discoloration or hazing left by the compounder (usually caused by running the compounder too fast or too long in one area), but repeated passes with the Cyclo will remove this. Be sure to move the Cyclo to a new position on the fleece once the pad becomes caked (usually after each four-square-foot sweep).

Numelin includes clamps with his fleeces, but I personally find it easier to just tie an overhand knot with the loose corners. Wrap the fleece around the Cyclo as tightly as possible—a loose fleece doesn’t buff nearly as quickly as a nice, tight fleece. Fleeces aren’t cheap, so I wash and reuse them once again for F7 buffing, and then dispose of them. I reserve new fleeces for buffing with S and final buffing. If you do wash your fleeces, do it at an industrial laundromat, unless you want to go shopping for a new washer.

Once you’ve removed the F7 swirls, clean the polished area with microfiber and mineral spirits, and move to the next grade. Although Numelin suggests going straight from F7 to S, some people do an intermediate pass using the compounder with C. I personally find that C compounding seems to easily haze and discolor, so I skip this step. Again, experiment and see what works best for you. As with F7, follow up C compounding with C Cyclo to remove the compound swirls, and clean up with microfiber and spirits.

You are now ready to Cyclo with S—this is the fun part! Cyclo with S really brings out the depth and clarity of the mirror finish. Since S is such a fine polish, it is not necessary to use the compounder first.

Once you’ve finished Cyclo with S, we next need to clean any remaining polish residue from rivet heads, butt joints etc. Unlike the previous steps however, you don’t want to use mineral spirits here since that would strip the protectant left behind by the S polish. Rather, simply wrap a new fleece wrap on the Cyclo and give the aluminum a final clean buff—you may be surprised how much oxide you can still pick up, even without any polish.

The final step is to sprinkle corn starch over the aluminum. The corn starch is a non-abrasive binder that will pick up any polish that escaped the fleece buff. Give the aluminum a good rubdown with your bare hands, working the corn starch vigorously into rivet heads and seams. Wipe clean with a microfiber towel, and voila, you’re finished! Shoot rivet lines and seams with an air compressor nozzle to make sure no corn starch remains behind in the nooks and crannies, as this can absorb moisture and cause corrosion.

Stand Back and Admire

Be warned of the shock you’ll receive the first time you roll your shiny new baby out into the sun; what looked like a perfect mirror finish under the fluorescent lights in your hangar now sports all kinds of swirls, hazy discolorations, and holographic sparkles. As Numelin writes in his polishing guide, “Sunlight is the ultimate critic.” Get used to it—there’s nothing you can do about it, and you are the only one who will notice. Everyone else will see a mirror.

Polishing is a lot of work, but nothing looks as sharp as a polished plane. As a side benefit, it’ll save you a few dollars (and a few pounds) on paint. Invest the time and effort with the course grades, and future re-polishes should be a piece of cake.

This article has focused on primary structures (wings, fuselage, empennage), but certain parts or locations of the airframe are not conducive to using the compounder and Cyclo described above. Stay tuned next time and we’ll discuss some tools and techniques for more detail-oriented polishing.

Photos: Eric Stewart