One of the most difficult jobs for any polisher is getting a high diamond finish on aluminum. Achieving a good shine in soft gummy material that constantly clogs stones and easily takes deep scratches from sandpaper is enough to challenge anyone.
Brushing and buffing can easily lead to grooves and lines in the finished surface and all the while the polisher still has to be responsible for holding tolerances on sizes.
This article will review proven step-by-step instructions for polishing aluminum, which if carefully followed will yield professional diamond finishes every time. This article also will provide useful and accurate pointers for those applications where a diamond finish is not required.
Common Problems with Polishing Aluminum
The most common problem associated with polishing aluminum is the deep scratches that plague the finishes. Three things primarily cause deep scratches in aluminum:
1) The wrong type of abrasive being used.
2) Too much downward pressure from the polisher’s hand.
3) Using too long a stroke while stoning.
Aluminum is primarily stoned by hand and easily turns to powder as it is stoned. This powder constantly clogs the pores of the stone and then builds up to “score” or “tear” the aluminum. Efforts to leave stones and use sandpaper yield somewhat better results. This method is the most commonly used today, but even stoning with sandpaper can leave a long, tough road of deep scratches, which refuse to diamond out properly.
The answer to the first problem is to use newly developed stones that are specifically made for all nonferrous metals (e.g., aluminum, copper and brass). If used with mineral spirits as the lubricant, these stones will never tear the metal! Even using these new stones while purposely trying to cause rips and tears won’t cause a tear. Check with your favorite stone vendor for samples of these newly developed stones for non-ferrous metals.
Stoning
The secret to getting a good diamond finish is to first have a fine scratch stone finish. The way to achieve this finish is to lighten up on the downward pressure as you stone (Second Problem). At first, you push down as hard as you need to in order to get rid of deep existing scratches, but then this time you go over the entire area with the same stone and a much lighter pressure. You will take out your own scratches! If a 320-grit stone put the scratches in, then take that same 320-grit stone and go over it again with a lighter pressure and take out the earlier scratches.
Next move up to a 400- or 600-grit stone. Test them to see what you like and pay close attention to the depth of all of the scratches at all times – look at them with a magnifier, compare them to each other, but do not put in any deeper scratches than what you already have. Always use a finer scratch to take out a deeper one and lighten up on your downward pressure until the very end.
You are basically “massaging” the grit in between the stone and metal. Don’t even let the stone touch the metal. Only massage the fine grit that is in between the stone and the metal. Pick small areas and see how quickly you excel at taking the deep scratches and turning them into fine scratches.
Stoning properly is not easy to learn and it may take forever to do, but with practice you will eventually become quite good. Practice on small areas until you perfect this technique of lightening up on the downward pressure.
Keep all of the strokes (Third Problem) down to two or three inches in length – because longer strokes tend to make deep scratches regardless of what type of abrasive you use and create deeper scratches going in the wrong direction. Now it’s time to diamond.
Diamond Polishing
Assuming that your work is wide enough, start by putting a one-inch cup brush into your rotary hand piece. If your stone finish is truly good enough, a diamond compound in the nine-micron range will work like magic; however, don’t feel bad if the nine-micron diamond won’t take out the stoning marks and you have to switch to the coarser 15-micron diamond. This just means that you need more practice at creating a fine stone finish.
Experiment with different bristle lengths. The longer the bristle, the longer it takes to cut. The smoother the finish in the metal and the shorter the bristles, the faster it will cut – but you run the risk of damaging the flat-ness of the job by cutting shapes and grooves into the aluminum.
Find a good balance.
Cool the brush only with denatured alcohol. Mineral spirits will make the brush cut much too fast – ruining the job. Be careful not to brush out deep scratches, because you will never end up with a decent flat surface – you’ll end up with a ruined wavy surface. Flatness comes only from a stone; over-brushing will only ruin the flatness. Wood sticks cut to shape can be used in a profiler machine with diamond to lap corners and sidewalls, if necessary. Once brushing is complete, it’s time to buff.
Buffing Aluminum
After a good brushing job, it’s time to do a soft buff, but before you begin it’s critical to take a good, long look at exactly how deep the brush marks are. They are probably only .0002 of an inch deep or less, so when you start with the buff, press down with less pressure. Be sure to use plenty of denatured alcohol to lubricate the buff and use a number three-micron diamond compound.
It’s best to have the buff loaded (fully impregnated) with diamond compound before you begin because at this point the buff is far coarser than the finish and only by having a fully impregnated buff will the point of contact be finer than the polish. With a fully impregnated buff only the diamond is touching the surface and not the buff that’s holding it.
Continue buffing until all of the brush marks have been replaced by the finest buffing finish you can get.
Rubbing Out by Hand
The final step is optional, depending on how good a diamond finish you need. Start by folding a piece of facial tissue into a square – six or 11 layers thick – impregnate it with number three yellow diamond compound, lubricate it with denatured alcohol and gently rub out any buff marks remaining. Be careful to use only two- to three-inch strokes by hand, so as not to cause scratches in the finish. Clean everything with mineral spirits first, then again with alcohol and you’re finished.
This method works on all types of aluminum and once you learn it you will understand how easy it is to do. Keep practicing on small areas or blocks of scrap until you see for yourself the “scratch range” you need to be in for the next step to work well.
There are many reasons to polish aluminum, such as:
1. Appearance
You can remove nicks, scratches, and other aluminum defects with polishing, resulting in a smooth surface. Plus, polishing can give the metal a clean, professional look.
2. Durability
Aluminum polishing can help improve the durability of the metal’s surface, reducing the risk of contamination and oxidation.
3. Corrosion Resistance
Polishing provides corrosion resistance, as it helps make the surface of aluminum more resistant to chemical reactions.
Many aluminum distributors understand the ins and outs of polishing aluminum. Of course, with the right supplies, you can polish aluminum on your own.
Use personal protective equipment (PPE) when you polish aluminum. Protective eyewear and gloves protect your eyes and hands when polishing chemicals and equipment. You can also protect exposed skin from the absorption of chemicals or metal with a barrier cream.
If you are working in an enclosed space, you may need respiratory protection. This helps prevent inhalation of chemical fumes or metal dust.
Additionally, tools used to grind and polish aluminum can be noisy, so you may want to wear earplugs or earmuffs to protect against noise hazards.
Lastly, as you search for tools you can use to polish aluminum, consider their safety features. Tools are available with variable-direction exhausts, which allow you to direct toxic fumes away from you while you work. You can pick up handheld tools with shock-resistant handles to protect against vibration and hand fatigue. There are even tools with ground fault circuit interrupters (GFCI) that help prevent electric shock.
You can polish aluminum in three steps:
1. Clean the Metal
Remove dirt and grime from your aluminum. With minor buildup, use a mild detergent. Wash the surface, rinse it, and dry it with a clean cloth or paper towel.
If there’s still buildup on the surface, you may need to use a commercial aluminum pre-cleaning product. Once you apply this product, let it sit for a few minutes to loosen the buildup, then rinse it off. Repeat the process if buildup remains. You can also use a stiff wire brush or fine steel wool to remove debris.
You won’t always be able to remove severe discoloration, scratches, and other surface flaws with cleaning or polishing. If you want to remove these blemishes from the surface of your aluminum before you polish it, you may need to sand them down.
2. Sand the Metal
Before you start sanding, apply masking tape to the areas of your aluminum you don’t want to sand. Along with this, put on protective eyewear and gloves.
With sanding, begin with a low-grit sandpaper and work toward a finer grit. In many instances, a 320-grit abrasive works well. If you’re dealing with deep pits or gouges, you may want to go with a grit in the 180 to 250 range. Generally, you should not go below a 180-grit abrasive since it may damage your metal’s appearance.
In terms of the grit to use when you sand the surface, work your way up. For example, you may start with a 320-grit abrasive to remove blemishes. Next, you can move up to a 400-grit abrasive to further prepare your metal for polishing. Depending on your project, you may want to go as high as 1,500 grit.
3. Polish the Metal
If you want to polish an aluminum pan or any other metal surface that will have food on it, make your own polishing compound instead of using a product that’s made from chemicals. You can make this compound by combining equal parts of water and white vinegar or water and cream of tartar (potassium bitartrate).
Apply a small amount of aluminum polish to the surface of your metal. Then, with a clean paper towel or cloth, wipe the surface using small, circular motions.
After you remove the polishing residue, use another clean paper towel or cloth to buff the surface. When you do, use the same small, circular motions as before.
For a large polishing job, you can use an angle grinder with an airway or muslin buffing wheel in lieu of completing the work by hand. When you use this tool, buff each section of aluminum and add more polishing compound as needed. When you’re finished, wipe down the polishing residue from the surface and change your grinder’s buffing wheel.
When you use a grinder with a buffing wheel for aluminum polishing, start with a coarse abrasive. For instance, you can begin with a gray metal buffing compound bar, move on to a brown tripoli, and finish with a white rouge buffing compound to give your aluminum a mirror finish.
I find it interesting how you elaborated on how the smoother the finish in the metal and the shorter the bristles, the faster it will cut. You mentioned a great point here, where I’m sure those looking into aluminium polishing will be glad to have learnt of. I grew interested in this after having a conversation with my father on industrial aluminium polishing last Wednesday night. This prompted my research into it and that’s where I found your great post! Thanks a bunch!
Polishing Aluminium material need special experience, thanks for sharing