EDM
The vast majority of jobs have been produced by EDM, both sinker and wire. The first step in polishing is to completely remove all EDM finish, and that is done with special stones. It is important to remove every last mark from the EDM finish, before going on to the next step. If you don't, the marks will show up prominently when you start to shine up the part. This will mean going back to the first step. In addition to being very good with the hands, our polishers have excellent powers of observation to determine when one step is complete in order to proceed to the next step. We recommend that the customer send in the EDMed pads before heat treating, so that we can remove the EDM finish much quicker. After heat treating, we can complete the polishing to the specified finish.

VARIOUS MATERIALS
Diverse materials require different techniques to polishing. For instance aluminum, years ago was much softer, and a mirror finish was not attainable. You couldn't use diamond compound and if you used a brush, a hole developed immediately, The only method to produce a mirror finish was hand polishing with an industrial metal polish. This produced a somewhat shiny finish, but had a lot of very small scratches. However today, the aluminum is much harder and it polishes very similar to steel. We now use diamond compound and can attain an very good mirror finish. It is common to use aluminum for short run molds. Beryllium Copper and other Copper alloys polish easily but have a tendency to show orange peel if the polisher in not careful. They can be brought to a mirror finish if they have been machined from a solid block. However, if they are made from a casting, it can lead to complications. A casting is porous and as one hole is blended, another one develops.

BEST EDM FINISH
Of course, the finer the EDM finish the faster the job can be polished. However, an extremely fine finish takes longer time to accomplish. The extra EDM time could be more expensive than the polishing time that would be saved. Experience proves that a relatively good finish, but not the best one attainable, is the most practical approach. From our face finish scale we selected the # 10 finish as the roughest one that would recommended. With the # 10 finish, and .001 material per side for polishing, we sould have no trouble bringing the mold to an excellent finish in a reasonable amount time while keeping the shape and dimensions. From rougher finish the time would be affected approximately 25% longer and dimensions and shape would be more difficult to maintain. The more stock you have to remove, the harder it is to hold detail, flatness and dimensions. If, on the other hand, the part was not restrictive in dimensions and had a simple shape, rougher EDM finish would be acceptable. It is best to check with us before you decide on which finish to use. The worst thing you can do when a job is late, is to go for a rougher finish on the EDM in order to get the parts to us a day or two sooner. That decision is a mistake, and will probably cost you more time and money, and lower the quality or the finished parts.