On 2010-09-27, Ignoramus21149 wrote:
On 2010-09-27, Karl Townsend wrote:

[ ... ]

I don't agree with Richard's analysis. His method assumes the
probabilty of a broken tap is the same on every hole. In fact, once
you've set up proper conditions and selected a top quality tap the
probablity of breaking goes with wear. Taps used in machines last
FAR longer than hand taps.

OK, good to hear.

I use OSG brand taps. Gun flute on thru hole, spiral flute on blind
hole. I forget, you aren't set up for rigid tapping??

Both your tension/compression tap holder and the procunier can be set
up in your CNC. But, its tricky. You've got to match feeds and speeds
to where the tap wants to be.

I understand, yes. If I run the spindle at, say, 200-300 RPM, then it
would take me about 0.2 seconds to stop the spindle, so about one
revolution. The floating tap holder should be able to take care of
that.

But you *really* should keep feeding according to the revolution
of the spindle on the index until it stops -- so your machine knows
where the tap is when it starts in reverse.

You think ER16 collets would hold a tap well enough?

The typical tapping head has a special chuck. It uses two ways
to hold the tap. A Jacobs Rubberflex type collet to assure
concentricity and a pair of plates with a combination left and right
hand threaded leadscrew connecting them to clamp down on the flats on
the end of the tap shank.

Some floating tap holders have similar chucks.

The main thing to consider is -- if it *does* slip and you are
doing rigid tapping, it will no longer be at the right depth for the
number of turns which the tap has taken.

I would look for something with the Jacobs tap chuck for this,
myself. And the Procunier or TapMatic tapping heads have them, along
with other features which make machine tapping easier -- including
automatic reversing when you start to back out of the hole -- while the
spindle is still turning clockwise. :-)

When doing tapping with a releasing tap holder in the bed turret
of my manual lathe, I've made tap holders which are simply the right
diameter for the shank of the tap, and a pair of setscrews opposite each
other to clamp on two opposing flats.

Good luck,
DoN.

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