Discussion in the shop today.
Fanuc G84 tapping = tool comes down to work, feeds in at rate calculated to
be correct lead for RPM, spindle reverses and tool comes back out.
Fanuc G84 Rigid Tapping = tool comes down to work, spindle stops and
orients itself, feeds down, spindle stops(dwell can be programmed: why?),
spindle reverses and tool feeds out. Retract rate can be set by parameter
to be as much as 4x the infeed.
For general tapping (a number of average, meaning no more than 3x tap dia,
thru holes or blind holes with plenty of room for chips) what would be the
advantage of one cycle over the other?
G84 tapping requires a compression/extension holder. Rigid tapping can
use a standard ER collet holder. G84 tapping requires a higher clearance
BTW, rigid tapping and synchronous tapping are synonymous.
The advantage for 3x the pull out is to reduce cycle time. I can't think
of an advantage to dwelling at the bottom of a thread. Maybe to reduce
heat before pulling it out at 3x the infeed. Fanuc also has a peck cycle
for rigid tapping as well. Pretty cool to watch.
I wonder if the outfeed is adjustable on a Haas VMC this way. I've not
noticed it just skimming through the parmeters. I use it every time I
tap on my Mazak M-Plus mill (H300 00%). We've got a large lot of
simple tapped blocks comming up on the Haas.
4x outfeed = each tapping cycle takes only 1/2 as long when compared to
compression...often this effects a very significant rate increase--esp.
where there are many holes to be tapped per pallet laod ( as in multi
parts-high density fixturing ).
LOL, gladly, nobody called me on this one/////
But, ACTUALLY..and given.5 SECONDS IN, with 5 OUT
= 1 SEC
TAKE THE .5 outcycle...and divide this by 4.....
Now add this to your "in time"....
Soooo...rather than cycle taking 1 second, its = to .625 seconds in this
Actually, there can be several advantages to using synchronous or rigid
tapping. How much of an
advantage you get depends a lot on the machine, and also on HOW the tapping is
some real basic stuff, to start with.
Real "Synchronous Tapping" isn't really synonymous with "Rigid Tapping". In
rigid tapping, used
by most controls, the infeed (usually Z axis) is kept timed to the revolution of
the spindle. This
eliminates the need for tension/compression tap holders, and can often create
better and more
accurate threads because there's no axial spring pressure on the tap. That
pressure can make for
slightly distended thread forms in soft materials, and can tear the first thread
at the top of a
hole when the tap is pulled by the holder as it exits. Tap life can also suffer
as a result of
rubbing on the thread flanks caused by the spring pressure.
Syncronous tapping, first used (to the best of my knowledge) by Brother, is
different. Instead of keeping infeed timed to spindle revs (one is independent,
the other is not),
real synch tapping is actually a genuine linear interpolation between Z and the
spindle. This is
typically only possible with smaller machines that don't have real massive
spindles, and which can
use something very much like an ordinary servo motor to run the spindle. But
the difference is
With real synch tapping, just like with any other linear interpolation, the
two axes match speed
perfectly (including accel and decel features), and both get to the programmed
endpoint at the same
instant. The interpolation is almost as good as what you get from X/Y moves,
except that the
spindle accuracy isn't improved by the mechanical advantage of a ballscrew. But
the two axes stay
in synch at ANY speed! There's no possibility of "overshoot" when you get to
the bottom of a hole.
When Z decelerates and stops at the programmed depth, S does exactly the same
With "Rigid Tapping" of the most common kinds, S still has to declerate
(slowly, clumsily) after
the hole depth has been reached. Z follows along, of course, so you can get
similar (though often
smaller) overshoot to what you'd expect from a tension/compression holder.
Better systems will look
ahead, and will decelerate S a bit early; but it's still a very approximate
thing - heavily
influenced by workpiece material, and by how quickly tapping torque will bring
the spindle to a
stop. The real depth of a hole won't be exactly what's programmed unless you're
turning the spindle
very, very slowly.
And that's the main functional difference - the part about turning slowly.
With real synch
tapping, you can tap as fast as you like, and still get excellent results. When
say, X and Y, you just naturally expect everything to work perfectly no matter
how fast or slow the
table is moving (unless you're working at extreme speeds). With synch tapping,
you enjoy the same
kind of accuracy and reliability. So, you can run ANY tap at speeds and feeds
that are right for
the tool and material, and not limited by the machine. 50 SFM for a 10-32 tap
would be 1020 RPM and
31.875 IPM infeed. And, if your machine has the accelerated retract feature,
you might back out of
the hole at over 4000 RPM and over 100 IPM on Z. And you'd do all that with
that the tap stopped right where it belonged, instead of running into the bottom
of the hole and
turning to powder.
With rigid tapping (as on a Fanuc control), you get somewhat better speed
significantly better holes, and probably better tap life. With real synch
tapping, you can get MUCH
better speed, perfect depth control, and all the advantages of quality and tool
I first got my hands on a Brother TC-211 tapping center in early 1985 (the
first one in the US);
and I've absolutely hated spring tap holders from the moment I tapped my first
hole on that unique
little machine. Fanuc, and everybody else, has offered "rigid tapping" for a
long time, as a way to
compete with the real tapping centers; but it just isn't the same thing. It's
good. It's better
than plain old G84, But it's a long way from really, truly making a tap behave
like it should.
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