Powder Buildup

Question:

 In your January 2002 issue, D.J. wrote to you about powder buildup problems with masking of threads. We have the same problems on some of our parts. We resolved the problem on most parts by machining after powder coating (we use polyester powder). Powder holds up with no problems (not even clamp marks), and we eliminated all the masking. All we have to do is a wash operation. I don’t know if it will work for D.J., but I thought I would give my two cents worth. J.G.

Answer:

Good suggestion. I forgot to mention this approach in my original answer. There are many applications where raw parts are powder coated before machining to eliminate masking. One such application was Singer Corp. who used to make sewing machines from diecasted parts before they switched to plastic. They would powder coat the raw casting and machine it afterwards, leaving all machined surfaces free of powder. This product was especially critical for visual appearance of the finish since the sewing machine operator was always in close proximity to the product and any finish related defects would be difficult to hide.