On 2010-09-27, Richard J Kinch wrote:
Ignoramus24898 writes:

I would like to drill and tap them with 5/16" drill and 3/8" tap, say
spaced at 1" interval. That makes for about 200 holes to be drilled
and tapped on my CNC mill.

How frequently do you break taps? If you're not an utterly reliable
tapper, you'll never be able to complete this job. Consider that if your
workpiece is ruined by breaking a tap, then you must succeed at all 200 in
a row. For a 90 percent chance of success, then, each individual hole must
be tapped with a 99.95 percent chance of success.

If you break a tap, say, once every hundred holes, then you have an 87
percent chance of failure on this piece (1.0 - 0.99**200 = 0.87).

Now you know why these cost $$$$:

http://www.edmundoptics.com/onlineca...productID=2929


Richard, I was hoping that I would tap on my CNC mill, so whatever
process I do, would be repeatable and not as random as manual tapping.

i