tap then paint, or paint then tap?

[kecked]

I think people also use a slightly larger tap by design to account for the surface coating. Pure guess here not based on knowledge...

[mixedgas]

Kecked is close.
You control the percentage thread depth by the selection of the tap drill. Prior to tapping. Most good tap charts will show the drill size for at least two percentages.
!
Steve

[laserist]

http://www.capsnplugs.com/masking-plugs/c/856

[planters]

Definitely drill and tap and then paint. Tell the painter to protect the holes, any pro will have those bungs. Any machining after painting exposes the parts to damage not only around the operation such as drilling, but from fixture-ing as well. Do not specify a loose thread fit to allow for an unknown variable such as paint which will wear out and change the fit over time. You might even want to sand blast which is a great prep for paint, but here the oil used in cutting the threads will ooze out of the holes, especially if you fill them with sacrificial screws to protect them from the blast. This oil will ruin the paint adhesion around the holes (been there). I have learned to avoid blasting steel and relied on a good painter to decide how to prep the parts. Good shops have ultrasonic and hot de-greasing baths. Go with a good painter and pay what you need to.