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).
I think, with the proper coolant/lubricant, good gun (spiral
point) taps, and the consistency of the CNC, he might be able to do this
with no problems -- with a high quality tap and a good hard aluminum
alloy. I would either use a TapMagic for aluminum, or just use WD-40 in
aluminum.
Even better for the task would be a TapMatic tap head (which
would eliminate the problem of feeding in reverse as you back the tap
out). The thing with at least some models of TapMatic heads is a
friction clutch, which you set up with a brand new tap so is just barely
does not slip when cutting with the proper lubricant. Then, once the
tap starts getting dull, it will slip and you can change out the tap
*before* it breaks.
I've used this setup in a drill press with 1/4-20 HSS gun taps
with 1/4" steel (making an apron for an old DiAcro sheet metal shear).
Now you know why these cost $$$$:
http://www.edmundoptics.com/onlineca...productID=2929
Hmm ... the code which that website has which wants to know
where I live is a pain. I can't find the right things to turn on to get
it to accept my data (cookies and JavaScript on, and it still refuses to
admit that I've given it a value and keeps asking. It probably wants
flash, which I refuse to turn on.
So -- I had to start over and click the [dismiss] button to get
anywhere since it would not let me back out to the original starting
point.
Enjoy,
DoN.
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