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topic 22096

Polishing Cast Aluminum


A discussion started in 2003 but continuing through 2019


Q. If I have a course Aluminum Intake Manifold (cast molded) and was wondering if there was a certain technique to getting this to a smoothed polished finish?

Chris Hoglund
- Auburn Hills, Michigan


A. Big job for you. Takes me usually 5___8 hours, going flat out. Always use a lubricant, I alternate between kerosene and vegetable fat. Use grit rolls of 80_120_240_320. You need about 15 of each grit. These rolls go on a tapered spindle in an electric die grinder, no faster than 3000 rpm. That was the easy part! Next, use hard felt cones and grey cutting compound all over. Don't forget the detail in nooks and crannies -- the hard part! Wash off with degreaser. Finish with a stitched cotton buff and tripoli all over. You must use a fast __3850, rpm and powerful machine for this. Forget adapting bench grinders or old washer motors, they don't cut it! To really brighten it up, use a spiral stitched cotton mop of two sections by 10 inch dia., plus hyfin compound sparingly. Good luck!

Mark Gunn
- NSW, Australia

How to finish aluminium small castings?


How to Cast Small Metal and Rubber Parts
from Abe Books


Q. I need some technical advice on the following:

1. What is the best method to get excellent surface luster and finish on cast aluminium curio items such as statuettes? I have seen some with excellent finish but I don't have an idea to produce the item myself.

2. What is the type of tank to be used for electropolishing solution (mixture of heated acids)? Our stainless steel tank doesn't last long.

Alex Abraham
- Ernakulam, Kerala, India


A. Vibratory tumblers work quite well, you will however round off the detail the longer it is tumbled for. With our castings (small lightweight high detail) we run them for several days in 3 stages of silicon carbide imbedded plastics, followed by a full day cycle in saw dust imbedded jeweler's rouge [paid link to product info at Amazon]. They come out with a great finish!

As for bright dip-electropolish tank, try a ceramic lined vessel. If you're like me and do this is in small quantities you can find the tumbler setups through jewelry suppliers, and you can even get ceramic lined containers in various sizes at your local grocery store.

Good luck!

Jason Aube
- Flint, Michigan

Polishing of aluminum sand castings

2005 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread



Metal Polishing Tips
from Abe Books


October 14, 2012

Q. Hi Pros,

How to get a good high mirror surface on cast ADC 12 aluminum without black marks? We are producing some 10-20 cm high solid aluminum items that are meant for indoor use.
We currently have 2 problems with this surface.

- Some items have black dots in the surface; can anybody tell how to get rid of them?
My guess is that after the casting process, when the items cool, there are particles in the air that contaminate the items.

- We get oxidation so the surface turns white-ish after 6 months; is there any way to close the surface of aluminum better? (I don't want to give the items any form of coating).

Thank you very much for you reply.

Finn Tranberg
Product development - Denmark

simultaneous October 17, 2012

A. #1 If it is not in the cast metal then it has to be the environment
#2 I think you have to define coatings. Oxidation can not be stopped, but you can slow it down and the only way to do that is to apply some form of protection with gas, liquid or solid.

tony kenton
AF Kenton
Hatboro, Pennsylvania

October 17, 2012

A. Finn,

What is the Aluminum alloy type? Some aluminum alloy can be electropolished to mirror finish (see pic attached of polished and non-polished pieces comparison).

polished and nonpolished aluminum alloy

It is more expensive than mass vibratory finish, but for some items it makes sense.

Anna Berkovich
Russamer Lab
supporting advertiser 
Pittsburgh, Pennsylvania 
russamer labs banner

October 19, 2012

Q. Hi AF Kenton

Thanks for reply. I also suspect the environment to be the bad guy!
Could you please give me some more info about how to slow the oxidation down, by gas, and liquid?
(Maybe with links or other)

Hi Anna B.

Thanks for reply. I am currently trying to get the spec. of the AD12, I will let you know ASAP.

Finn Tranberg
- Denmark

October 25, 2012

A. I would be reluctant to suggest a protective coating until you correct the problem of the spots. Gases are not very economical protective systems, so I'd look into liquids. Any petroleum base product offers some protection. Again you need to define your needs in the way of protection and use.

tony kenton
AF Kenton
Hatboro, Pennsylvania

July 4, 2016 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I recently purchased a large box of aluminum castings used for jewelry and other items. Some is rough cast and need sprues removed, all the way to polished but uncoated pieces. I know how to remove casting marks with a grinder, but the castings are rough (sand cast). Will a tumbler or vibratory tumbler polish out these pieces? (What type media?) And do I need to seal the finished (shiny) pieces as they still will leave dark aluminum residue on skin, etc. Any ideas? Thank you!

Teresa Wallace
artist - Okla City, Oklahoma USA

July 7, 2016

A. If your castings are rougher than 35 RMS you can try a fast cut (rough) ceramic media in a vibe.The larger the better for speed or a time period 4-8 hrs or more. After that you, you may want to go to a coarse plastic media for a couple of hours or until smooth. A third step brightening can be done wet or dry.
All metals will oxidize over a period of time. The sooner you can protect them the better.

tony kenton
AF Kenton
Hatboro, Pennsylvania

January 21, 2019

Q. Hello hope you all are doing well over there.
We are making some cast aluminum products but we are not getting the desired surface finish while turning. There are some people in Agra city of India who are doing the same thing. They are getting the finish like chrome while turning ... but the problem is they are not telling is their technique. What should we do to get chrome like surface finish on lathe?
Do we need some kind of special bit metal or lathe hand made tool? Please suggest something and helps us to reach our goals.
Thanking you.

Mohd Gulzaib
Aluminum utensils - Moradabad,U.P,India

January 2019

A. Hi Mohd. Please fully read this thread then search the site for "polishing aluminum". How do you know they are doing it on a lathe? If they are doing it on a lathe, I would be virtually convinced that they are doing a multi-step polishing sequence as described here, not turning to a chrome-like finish. If you are attempting to reverse engineer someone else's process, you should get some of their parts and do a full inspection and metal analysis so you are 100% confident that their material is absolutely identical to yours. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Striving to live Aloha

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