In article ,
"Bob La Londe" wrote:

Someday I'm going to get to buy a good used tapping head that doesn't go up
to almost new price.

Anyway, in the mean time I have been looking at the various taps and
suggestions for use with a tapping head. It seems like a regular straight
tap like comes in every generic tap & die set can't, or at least shouldn't,
be used in a continuous tapping machine. The stuff I've read seems to say
you need to use either a spiral tap or a gun tap.

Yep. The standard straight plug tap needs to be reversed every turn or
so, to break the chips, and backed out to clear the chips. Gun taps are
far better.


Here is what I understand about the two types. Please correct me where I go
wrong.

BOTH. Both are designed to move chips out of the hole.

Gun taps shoot the chips forward and are suitable for through hole tapping.

Spiral taps conveyor the chips up flutes on the tap and back out the top of
the hole and are suitable for blind hole tapping.

Yes.


Here are my questions. Should you only use them as described above? Is
there any reason not to use a spiral tap for both through holes and blind
holes? Obviously the gun tap would have a problem in blind holes if tapping
to depth.

When hand tapping, I often use a gun tap in a short blind hole, but with
care. I manually remove the ball of stringy chips, then finish the job
with a bottoming tap.

If the blind hole is deep enough, one can skip the followup with the
bottoming tap, but one should always remove the ball of chips, lest it
get into the threads and jam the screw.

Joe Gwinn