Guidelines for acceptable rack marks and other non anodized areas

A. There's no fixed answer. Every buyer must understand that some rack marks are inevitable, and every anodizer must try to minimize them. After that it's a matter of negotiation between purchaser and supplier to find a size and location both can live with.

A. There are no "guidelines" per se, although any anodizer with his salt will try to keep the rack marks to a minimum, keeping in mind that he must be able to hold the part securely, and make good electrical contact throughout the anodizing process. If you are the customer, you should be able to work with your coater on an acceptable size, and location of the rack marks.

As far as the blind hole question goes, keep in mind that the deeper and smaller diameter the hole, the more likely you will get an air bubble trapped inside. Also, lets say you were anodizing a cube, and each side had a blind hole. Odds are that at least one of the holes will potentially trap an air bubble, depending on the hole size and depth, and how the part is racked.

Your thread question is extremely vague. Usually, most tapped holes should be masked for anodizing.

A. Hector

The customer usually specifies (or has authority to) where rack marks are permissible, and their size & number. If not specified, the supplier uses best available methods (will vary from shop to shop) and typically is a matter of economics (what is the easiest)rather than part quality (what is the best).

If unspecified, holes, threaded or not, over 1/4" should be anodized. Should, not must.

Download a copy of the spec at http://assist.daps.dla.mil/quicksearch/