"Tim Wescott" wrote in message
...
On 12/14/2010 07:29 AM, Bob La Londe wrote:
"Bob La Londe" wrote in message
...
I've got this urge to own a tapping head, so I've started doing a
little reading on tapping speeds. One formula I have read is:

For inch taps
RPM = SFM / (.26 * Tap OD)

http://www.newyorktwistdrill.com/tap...l_data_03.html

A middle of the road SFM for aluminum ( I know it can vary
dramatically depending on hardness, alloy, etc ) is about 600.

When I plug that in for a 1/4" tap it comes up with 9230.769 That
seems insanely fast to me. Are you guys who do this really tapping
holes in a fraction of a second?

Seems like for small jobs the clamping and positioning requirements to
do that would take longer than tapping a couple holes by hand.


Oh, heck. They also list aluminum on their chart at 90-100. Now I am
really confused.

At 95 that comes out as 6.175. That makes more sense, but then it
becomes a problem to turn that slow and still apply full power with most
machines guys like me can afford.

??

95 / (0.26 * 0.25) = 1462

And why do they list aluminum at 90-100 and many of the milling sites
list aluminum from 500 to as much as 1200?

I had thought up until this moment SFM was SFM.

Maybe the operation does matter.


I totally hosed that one hey Tim. LOL.