On 09/27/2010 10:13 AM, Ignoramus21149 wrote:
On 2010-09-27, wrote:
For aluminum, you may want to use a Thread Forming Tap, instead of a
Thread Cutting Tap...Since you will be using coolant/cutting fluid,
the going will be much easier, and the thread will be stronger. A
thread forming tap has the additional advantage of no chips.

That's a good idea. Would you say, with a proper tin coated tap like
this, and using a letter S drill, the 3/8" holes can be tapped
consistently on my CNC mill?

i

You use an entirely different drill size (much larger) for a thread
forming tap. The workpiece is pushed out of the peaks to form the
valleys. The tap manufacturer should be able to recommend the correct
drill size.

Jon