Tool steel is a hardened form of carbon steel specially made for durability when made into various types of tools. The hardening process involves heating and cooling the steel and quenching in water, oil, or air.
The part on the left was hardened using an oil quenching process. This led to enough oil getting baked onto the surface that the part could not be plated successfully. Additionally, the part needed to be lightly deburred and the edges slightly rounded to get better adhesion of the plating material.
Most times, steel is deburred with Ceramic Media as that is the most aggressive type of tumbling media. This is especially true for hardened steel. In this case, however, the parts are going to be plated. Plating is a very thin coating and will often ‘translate’ any imperfections that are on the surface prior to plating.
A Plastic Tumbling Media was used to get the finish on the right. As you can see, and with a long enough cycle time, this less aggressive media was able to round the edges, deburr the part, and leave a smooth, nearly polished surface finish ready for plating.