polishing

Getting aluminium to look good after all the cutting and filing is done can be accomplished in several ways. It can be painted, powder coated anodised, polished, brushed or just left raw. Here I’ll show you how easy it is to polish aluminium to a beautiful mirror finish. If you know that the end result of your work will be a polished part then, steps need to be taken as far back as when you select the material for the part. To keep your work to a minimum, select a piece of metal that is free of any deep scratches or dings. As the work progresses, be aware of the need to protect the surface of the part so that when the time comes there is less sanding and cleaning up to do before polishing.

After all the shaping, drilling etc is done, the part will need to be sanded in preparation for polishing. On a good quality surface it’s fairly safe to start sanding with 240 to 360 grit. You will need some water for wet sanding and a sanding block (to keep sanding even and prevent dips and furrows).

So beginning with around 240/360 grit gradually sand the surface and the edges, progressing through various grades until you arrive at a surface that has been sanded with at least 800 grit. I have not gone any further and achieved good polishing results but I would still suggest going beyond this and sanding all the way down to 1200 grit. How you sand, whether straight back and forth or in a circular motion is up to you and experience will teach you which will suit your needs. In practice, once you get down to 1200 grit and beyond, the polishing process will get rid of the tiny sanding marks anyway.

There are a lot of things that you will need to get a ‘feel’ for yourself and only playing around for a while will show you what is possible. I used to sand all the way up to 2000 grit and found that this was not necessary. I now only sand to 800 grit and use all the wheels as you’ll see below. The important thing to remember is, try out all the variations yourself and get to know the process (it doesn’t take long) you will soon arrive at system that is efficient and suits your needs.

The polishing can be done several ways, depending on your budget and the facilities you have available. Perhaps the cheapest way to do it is to get a polishing kit that only requires the addition of a power drill. The photo at the bottom left shows one of these kits. It comes with a felt wheel and a rag buff, together with two types of compound and the arbour to fit the wheels to the drill. On an even smaller scale a lot of the ‘Dremel’ knockoffs have small polishing attachments included with a bunch of other fittings, see photo, bottom right.

Probably the best way to do the polishing, and the way I’ll describe in detail, is to use a bench grinder with a special attachment for polishing wheels.

I don’t have enough room in my small workshop, so what I’ve done is to lay a slab next to one wall and fitted a home made grinder stand with some Dynabolts. The stand was easy to make with just three pieces of steel I had cut to the right size at the iron monger. Drilled some holes and welded it together. With the grinder fitted, it’s covered in several layers of plastic for most of the time until I need to use it, and the weather is permitting.

The polishing wheels that are used with the grinder, are available at the hardware shop but they aren’t cheap. The photo at the left, second from the bottom, shows what you will need. From the left, the wheels with the corresponding compound. First is the sisal buff to be used with only the grey compound. Then, the stitched rag buff and the brown compound, and lastly, the loose leaf rag buff and the white compound. If, like me, you polish aluminium and acrylic, then keep your buffs separate and only use them for one type of material.

You will need to wear breathing protection while polishing because the rag buffs disintegrate in the process and release a lot of tiny fibres. Also, tiny bits of aluminium and compound get thrown off and you don’t want all this crap going into your lungs. Gloves are a good idea as the process is very dirty and eye protection is non negotiable. (I’m wearing mine while taking this photo).

ALWAYS WEAR EYE PROTECTION AND DUST PROTECTION WHEN POLISHING.

To fit polishing buffs to a bench grinder you’ll need to buy one of these adapters. They only cost about ten bucks from the hardware store and as well as holding the buffs, it extends the grinder shaft giving you more room to move around the wheel. The buffs just screw on.

Now it’s not a hard and fast rule that you must use the stitched sisal wheel first. This wheel is fairly aggressive, and if you’re not careful, and the surface to be polished is nice and smooth, then this wheel may put extra marks into it. So try it out and use it without applying too much pressure.

Load the wheel with compound and begin polishing moving up and down, and side to side. Never stop moving the part as this will result in an uneven surface finish.

When the surface is uniform and further polishing yields no improvements then, you know it’s time to move onto the next wheel.

If you have a particularly well prepared part, that’s been very well sanded down to a very fine grit, then this will be the first wheel to use. This is the stitched rag buff and is used with the brown compound. Again, load the wheel with the compound and begin to polish. Keep the part moving and stop from time to time to wipe away the compound with a soft rag to check progress.

You’ll know when to stop polishing with this wheel when the surface is even and no further improvement can be achieved.

The last wheel is the loose rag buff. This is a very soft wheel and is used with the white compound. To use this wheel just follow the same steps as for the other wheels. Once the surface is polished with this wheel and the compound is cleaned off by buffing with a soft, clean, cloth, then you should see a beautiful mirror finish.

Polished aluminium parts are really pretty, especially when these parts are in combination with anodised or painted parts and surfaces, or even wood.

Just to recap. Polishing really is very simple and anyone can do it after just a little practice. The most important thing to remember (after safety) is to keep the part moving while using the buffs.

Be aware that the views and opinions published here belong to the author. Guides included on this site are the way I do things and are not an exhaustive or thorough examination of the subject under discussion. There may be different and better ways to achieve a desired result, the best advice I can give is ‘look around’, there is always a better way to do anything.