I use spiral-point plug taps exclusively. I think hand-taps are a
*complete* waste of time, even if taping by hand. Spiral-point taps do
not require any reversing until the hole is completely threaded. I
don't see any drawbacks other than taper hand taps are perhaps easier
to square by hand than plug taps.
If it is pre-tapped - use a plug. If there is a bottom hole issue - plug.
If it is a new tap - use a taper and then a plug if needed. Tapers start nice.
Simple as that.
Then, there are different taps that have ? H(number) ? and that indicates
the effective depth of cut or % of cut.....
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Endowment Member, Golden Eagle, Patriot"s Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
Want to give that some more thought, Roger?
Plug taps are generally used when power tapping, where starting the thread
isn't an issue. There is almost no need nor reason to use a taper tap in a
production environment. Fact is, they're pretty much relegated to hand
Through holes are generally tapped with spiral pointed gun taps, and
anything less is a stupid idea. You can tap a hole and be back out of it
in something like 5 seconds by using that kind of tap.
There's lots more to this issue than how simple it appears, depending on
Close-----but no cigar. If there's a bottom issue, use a bottom tap.
That's what they're for. Almost no lead, and difficult to use, but
effective for getting that last couple turns. It's nearly impossible to
start a hole with one.
Only by hand--------and never, ever, power tap with hand taps unless the
material in question is very thin. It's an instant recipe for a broken tap.
There is no need for taper taps when power tapping.
No-----it indicates the theoretical pitch diameter of the tapped hole.
Drill size dictates the depth of cut.
Most of my tapping is performed using a Bridgeport or lathe.
(sometimes an electric drill in control panels).
The most crooked hole I have ever made was with a 5/8 NC taper tap by
hand. I got it a bit crooked and it kept going and going off axis.
My curiosity was peaked by thinking, all these taps cut one thread per
revolution. To some degree, the torque required should be the same
unless the depth of cut is a major factor since Bottom > plug > taper.
Elucidation on the subject will be well received.
I won't claim any expertise here, but I think that is a bad
Each of the taps - unless it is a tap whose taper length exceeds the
thickness of the material - will remove one full thread's worth of
material with every revolution. The torque necessary to remove that
material depends on the amount of material removed, but it also
depends on the width of the cut. A bottoming tap without any taper
might remove all of the material with one tooth. A taper tap with the
taper ground for six threads would cut over at least six teeth, or six
times the number of flutes. I'd have to think about that one a bit -
I suppose the accuracy of the tap would determine how many teeth
actually do any cutting.
I think a long taper tap might be like a taper reamer. You take off
very little material with each turn of a taper reamer but, because of
the long length of cut, it takes a lot of torque to turn.
The problem with bottoming taps is the point load, or load per tooth. It's
dead easy to break a tooth in tough materials---whereas with plug or taper
taps, the chip load per tooth is much lighter. Load on the shank may or may
not be the same. As a result, those of us with experience tend to avoid
bottoming taps, but instead use a modified plug tap that has been somewhat
shortened, and go in a tapped hole to remove just the small amount needed to
establish full depth. The shortened tap usually allows for a couple more
turns. Just like a bottoming tap, they don't start well, but are good for
cleaning out the tapered portion of an existing tapped hole.
It's usually desirable, if you're trying for a full thread depth, to use
taps progressively (when hand tapping), so each tap removes a little more of
the material, yielding less for the bottom tap to remove. That lowers the
You likely realize that there are variables, and what works one time may not
another. Doesn't hurt to have a background in tapping, so you have
experience to call on to address questions that may arise.
Chuckle! Likely so. Still, I understood what you meant.
There are several phrases that differ from one side of the pond to the
other. I always chuckle when I see the word "swarf" used for all chips.
Swarf, here in the States, is connotation for the fines generated by
something like a grinding wheel. Ever notice they offer chip removal
systems with production machines, not swarf removal systems? :-)
Get well, Mark!
Gun taps are two or three straight fluted taps with a spiral pointed end.
By design, they make poor hand taps, but work well when power driven. The
design of the spiral point drives the chips ahead of the tap, so you get a
set of chips that are intertwined from the opposite end of the hole, usually
an unbroken rope, so to speak. Such a tap will work for blind hole
tapping, but the hole must be deep enough to allow the chip to accumulate,
and can be difficult to remove unless you can break it up after tapping.