Minimize the Impact of Double-Blind Holes

Some parts have what we call double-blind holes, and they can be a real challenge from a rack electroplating standpoint.

The parts shown in the photo below have the exact same holes on the bottom that you see on the top. The term “double blind holes” refers to the fact that the holes aren’t connected; they don’t run all the way through the parts.

If the parts are hung on the rack in such a way that the holes on one end of the part are lower than the holes on the other end, plating solution will not enter the bottom holes since air bubbles will form inside the holes. However, plating solution will enter the top holes, and that causes a problem: Once the parts have been plated, dried and emptied into the parts’ shipping container, the solution that was trapped inside the top holes will bleed onto these parts as well as other parts in the container. This creates the cosmetic imperfections indicated by the arrows above, and it can also lead to corrosion issues down the road.

There are three things you can do to minimize the extent of this problem:

1. Have your zinc electroplating done by company whose rack plating specialists have the necessary expertise to fixture your parts to the rack tooling in such a way that plating solution doesn’t enter either hole.
2. Manufacture your part with a relief that connects the two blind holes and allows the solution to completely drain out of one end or the other.
3. Insert Teflon-wrapped bolts into the holes prior to sending them to the plating facility. The goal of this is to eliminate as much air space as possible to minimize the amount of solution that can get trapped inside the hole. For this reason, it’s also recommended that you not remove the bolts until at least a day after the plating process so any solution that does get trapped can dry and not bleed out onto the part or adjacent parts when the bolts are removed.

 Any way you slice it, parts with double-blind holes pose a challenge for both you and your plater. Fortunately, we know of a zinc plating company based in Reedsburg, WI that’s definitely up to that challenge!