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Cross drill before or after powder coating?

I am quoting a job where the 1® x .049 ERW tubing is to be powder coated. The tube has several 5/16" holes in with a requirement that no paint inside tube. Do I drill the holes after the painting process? Will the clamping fixture mar the finish? Will the paint chip off?

Michael Heuser
Tube Products - Racine, Wisconsin
2006

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2006

If you want to be absolutely sure of no paint on the inside of the tube, you have two choices: drill the holes after painting or drill the holes and plug them before painting. Obviously, plugging them is a large labor requirement. Even though the holes are small, some powder would inevitably make its way in there.

As for marring the paint or it chipping, you'll have to talk to your paint supplier. They should be able to provide a formulation that's ideal for your needs.

With a good paint and good pretreatment, your paint should stick to the part even if you drill it. I've had several customers that bolt painted parts together with some high torque ratings. Unless the pretreatment is out of spec. or the paint isn't cured properly, they don't have problems. In fact, paint popping off during assembly is sometimes their first hint that something isn't right elsewhere.....

Christian M. Restifo
- Pittsburgh, Pennsylvania