Sand cast bronze, how to continue?

[marinesteam]

I have some newbie questions regarding polishing sand cast gunmetal (bronze).

I am in the process of building a marine steam engine and many of the parts are sand cast bronze. This is a newly manufactured engine that represents ones from the Victorian era and I would like to have as much of the bronze be "bright" finished to keep with that look.

I am currently removing the sand finish from the castings using a combination of flap wheels, sanding disks and cartridge rolls. Most of the surfaces are curved, filleted or hard to reach, but with these abrasives in either a straight or right angle die-grinder the work is progressing fairly quickly.

So here is my first problem and question. It seams that I can only easily find the flap wheels and small roloc disks in grits up to 240. The cartridge rolls only seem to come in grit up to 180 grit. My question is: once I have done as much sanding as I can to remove the texture of the sand casting, where should I go next? The Caswell site and the buff chooser says to start with black compound (emery) then brown and finally white but is unclear as to the starting condition of the metal. If I have sanded to 180 grit can I start immediately with the black or should I go through the grease less range from 180 to 400 before using the emery? Or is there some other progression that I should use?

I am planning on buying compounds and buffs from Caswell but would like to limit my shopping list to the items that I will really be needing.

Thanks in advance and sorry for the length of the post.

Ken
Marinesteam
Colorado, USA

[jrow]

marinesteam,

First off you can get cartridge rolls in finer grits. I have some in the 320 grit. Check 3M's web site, or there may be a machinists supply place in your area that has finer grits. They come in all sizes and grits.
I would start with sanding up to 400 grit and then use your Emory compound, OR you can use greaseless up to 320 grit and then start to polish with Emory.
Make sure to get buffs sizes that will get into all the places that you need to buff.

John