The parts pictured here are cast bronze with some subsequent internal machining. As the part comes out of the casting and machining process, there are burrs on the threads and the surface finish is rough and dull.
A two-step process to first deburr and smooth out the finish and then to brighten the surface was used. The challenge is to identify media that will get to all areas necessary but not get stuck inside the part.
The first step used a small, triangular Ceramic Media in a wet tumbling step. A smaller media was used to get to the burrs and threads which are interior to the product but not get lodged in any of the holes in the part. A triangular shape was ideal to smooth out the surface finish all the way into any corners on the part. The result after this step in seen on the left.
The polishing step was dry tumbling using a Premium Treated Tumbling Media. This grit-based media is ideal as it will polish all areas of the part, even inside the threads (see part on right). This is a longer cycle time but worth the wait given the finish.
For reference, note the inevitable imperfections – divots, bubbles, small ‘channels’ – in the part caused by the casting process.