Mirror finish

Wayne wrote in news: snipped-for-privacy@news.starband.net:

Lots of passes with abrasives of increasing fineness of grit.

I usually start with 180 grit and progress to 2,000 or even finer.

The polishing begins where the mill leaves off for most of the stuff that I do...

Sand with progressively finer grits, then buff with a polishing compound. I've used a product called Simichrome but I'm sure there are better buffing compounds around. Check

for starters.

A good face mill, CNC, high rpm, coolant, lite cut can produce a near-mirror finish. As will the right lathe tool in turning. Will greatly reduce subsequent sanding/buffing/polishing.

Could also be anodized and laquered, which gives that high-gloss shine.

They coat telescope mirrors with aluminum, so it can take on a very shiny finish. I used to use Simichrome on my aluminum parts (after sanding w/finer and finer grits as previous posters mentioned). Trouble with Simichrome is its cost and that little tiny tube. I've since found that Mother's metal polish is probably an even better polish AND you can get it in 10 oz. jars (haven't had to buy any for years).

Nok

Emery and a sisel wheel will clean up machining marks, then go to a spiral-sewn muslin wheel with red rouge.

Sanding with progressive grits is slower (a lot slower), but also safer. There is a portal to another dimension behind every buffer!

3003 and 5052 sheet comes from the mill with a bright reflective finish. The 3/5000 series is not heat treated so it doesn't have the gray heat burn that is typical of the 6061 you see in every weld shop. There is also a product called 2024T3 alclad which has a thin layer of pure aluminum. These grades are available from suppliers with a protective coating for handling. You usually have to buy at least half sheets and you take your luck as to whether the finish is intact. If you specifiy the finish when you order the material you can return the ocasional damaged sheet.

Bud

I once saw a piece being turned on a lathe that was a true mirror finish. At first I thought it was just a mirror spinning, but close examination proved a cut was being taken and the finish was mirror before and after the cut. VERY fine cut, diamond tool bit. Committees of Correspondence Web page:- tinyurl.com/y7th2c

On Thu, 22 Mar 2007 00:05:02 -0500, with neither quill nor qualm, Don Foreman quickly quoth:

Unfortunately, I learned that with a 7" buffer on cars at the Vista Car Wash at an early age. Oops, there's metal under that paint! The owner finally bought a d/a (random orbital) model. What a safe and lovely difference!

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I referred to 8" wheels on a 2 hp 3450-RPM buffer. When(not if) it grabs something.... there's a reason why there's a (dented) backstop behind it, and why work is always held so when(not if) something grabs it'll be propelled *away* from the fool in front of the tool. But oh, my, does it get the job done RFN! Wear welding gloves; the workpiece gets hot fast!

If the mill doesn't give you the finish you require and you need to use a buffer, I've found Caswell to be a good resource.

Peter

Mirror-finish sheet is calendared - the last roller in the rolling mill has an incredibly high polish on it, and it replicates that polish onto the sheet.

I don't know of any way to get a mirror finish of that quality without a lot of work. Small pieces can be flycut with a low axis feedrate, that will get you a very good finish. From there, you could use buffing wheels and polishing compound. I have made solar concentrating mirrors using a humongous buffer and jeweler's rouge. We'd run the buffer until the exhaust air from the motor was ready to burn the skin off your arm, then give it a few minutes rest. They do this on competition aircraft. The deal is you have to get the aluminum, the buffing wheel and the rouge's wax base hot enough to be near-liquid. This exposes the abrasive to the metal. We took an 18' radar dish with a typical spun-aluminum finish up to a dazzling mirror polish in a couple of days, once the Prof. realized he was going to have to buy a professional-grade polisher. He realized that after we made a brand-new Craftsman (or similar) polisher go up in real, honest FLAMES in less than an hour. This was in 1974, when Craftsman wasn't the joke it is today.

Jon

On a telescope mirror, the aluminum coating is to reflect light! The mirror has already been figured and polished to within 1/4 of a wavelength of light or better before this! I have actually made some telescope mirrors, and eyepiece lens.

Steve R.

I polish aluminum and other soft metals with a paste of Brown Tripoli, and oil. Most good tool dealers, and some hardware stores sell this in assortments of buffing compounds. I have a bell metal (bronze) burnisher, and several polished steel ones. The paste is put on the burnisher, and the tool is applied to the bottom of the rotating work piece. Keep the burnisher moving to and fro for a good even polish. Flat or irregular forms can be buffed with the same compound, but no oil.

Steve R.