finishing bronze castings

[bischoffboatworks]

Hello all,
I just purchased a bunch of bronze fittings that just came out of the sand-castings. Does anyone know the best way to finish these parts... they are still nubby from the sand. I thought of a grinder but there are many rounded, concave, convex, etc. surfaces. Thanks for ideas.

[Jay Greer]

Depending on what you are seeking in the way of finish, you can use a stationary belt or disk sander for flattening areas that are slightly concave from shrinkage. A polishing mop or sand o flex wheel that is made up of strands or strips of emery cloth can be a great aid for cleaning off flash. Tumbling can also produce a matt finish if you send your parts out to a service. Final brilliant polish can be done with a series of felt cones and buffing wheels and buffing compound.
Jay

[Bruce Hooke]

There are many tools that can come into play here. It partly depends on how much you want to spend on tools:

1. Don't overlook good old hand files. Particularly for tight areas they can be very effective. Used well they can also be surprisingly fast.

2. A die grinder with various small bits is also useful for tight areas.

3. Various types of sanding belts are great for the areas that can be gotten to with sanding belts. Use really course grit Zircon belts/wheels if you can find them.

4. I use a stitched cloth wheel painted with a special cement used to adhere silicon carbide grit to the wheel...paint on the cement and then roll it in the silicon carbide grit. Mount on a pedestal grinder.

5. Various "grits" of Scotchbright pad are very useful for getting from the surface left by a sander or grinder to something a bit more refined.

6. Expect that somewhere along the line you will uncover small hidden voids in the casting. In my experience this is normal. If the foundry you got the castings from is nearby you may be able to get them to fill the voids.

I hope you got a good deal. A large part of the cost of a bronze casting is the finishing work! Only go for a highly polished finish if you are a bit of a masochist!

Be careful around metal and power tools. Metal is sharp and hard and can easily get grabbed and thrown around or jammed into you. Metal shavings are very bad for your eyes.

[merlinron]

bruce's suggestions are spot on. ihave finished a fair amount of metals and it is almost impossible to accomplish a good finish without using files somewhere/sometime on most of the pieces. the idea is that you get allot more control over shape with a file. usually a piece will be filed first to obtain the general contours, then hit with a wheel depending on the job at hand with grits depending on the finish desired. finally, a file again, drawfile style, in places such as edges to give the piece's shape some real definition. one place to watch is the edges where the piece mates to the wood. a good relatively sharp and square to the bedding surface edge there wille look much better than an edge that is "wiped out" from a buffing wheel.

tumbling may be ok with some parts but generally it does no good for these edges at all.

hide glue is what is used to load a buffing wheel with a dry, loose polishing grit. heat up an amount roll the wheel thruogh the glue and then roll it through the desired grit. there are also available, compounds that are suspended in a latex based adhesive, they come in a sausage sized tube. you strip some of the tube off and simply hold it against the spinning wheel to load. grits are available from about 200 to 600 they are fast and convenient but considerably more expensive to use because they don't stay on the wheel as well as a dry grit loaded on with hide glue. the bigger grits will cut real fast and on ferous metals will throw sparks..... you can ruin a piece pretty fast if you don't watch out!
a good pair of leather gloves is just about manditory for this kind of work. bronze will get very hot and stay that way for a long time when polishing it on a wheel. i use welding gloves for thier insulation.

[Thorne]

Let me second that last bit about the heat -- got a nice burn on my finger after grinding bronze and then wondering why it turned that funny dark-gold color.

I use a wire wheel on a right angle grinder to polish small bronze hardware - a full faceshield is absolutely required as these toss bits of wire in all directions.

[Bruce Hooke]

Just as an FYI, to glue loose grit onto a wheel I use "Polishing Cement" from M.P. Iding Co. http://www.mpiding.com/ (yes, their website really is just a home page with their name and address and nothing else -- don't hold you breath about the under construction part either...just pick up the phone and call them and then I think you'll have to send a check) but unless you plan to make a regular habit of finishing bronze castings this is probably not the most sensible route.

Oh, and I get the grit from McMaster.

[S B]

It' been a while, but if my memory serves me right bronze is quite maleable and flashings can be cut with a sharpe cold chisel. The first thing I would do is sandblast the castings with a semi hard agregate like saw dust, it won't pit the bronze just remove the dirt and oxidation. After removing the flashing the scar left can be worked into the piece with a hammer. Abrasive cutting tools are able to create more work than you started with, and you may use a lot of discs, belts etc, but itis unlikely you will wear out your hammer. It isn't unpleasant work either.

[bischoffboatworks]

Thanks so much for your input. You guys are great!

[Thad Van Gilder]

I have been doing most of my cleanup work with a random orbitol sander.

-Thad