Tooling
Options
for
Turning Machines
The
tool turret was a grand innovation – it provided a wide selection
of tooling on one machine. Many
part types could be machined without constantly changing the tools.
CNC
machines incorporated the idea with the indexing turret.
But as CNC machining gets faster the indexing turret has
become the source of lost cycle time.
The pluses of the turret are the flexibility and versatility
of the tooling. The down
side (there is always a down side) is the time lost for each
retraction, index and protraction of the turret.
Machine
tool builders are aware of this problem and they are producing
machines with faster and faster index times along with faster axis
rapid movements. Machine
tool sales people often quote “chip to chip” time, illustrating
the quickness of their machines.
With
a new machine, you might get faster indexing time, but what about
our older machines. An
older CNC machine with a large diameter turret may waste up to 30%
of the cycle time with idle movements between cuts.
Another
tooling system is the gang style lathe, popularized by Hardinge
machine tools. I work
with this tool system in our Citizen swiss machines and know that
gang style tool movements are pretty quick.
Here’s
an idea to combine these two tooling systems to improve cycle times
on our older conventional CNC lathes.
This idea is not new, it’s just been re-born to make our
life a bit easier.
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We’ve
built a gang-style tool block for our indexable turret.
This tool block has a 2.00” shank which mounts directly
into an ID tool station on the turret.
There are 3 precision mounting 0.750” diameter holes
designed to accept ER style tool holders.
When
mounted on the turret this tool block provides the flexibility of
the turret with the quickness of a gang style machine.
We can install a spot drill, a twist drill and a tap into the
tool block and rapidly perform all three operations without full
retraction and indexing of the turret.
You need to check the X axis stroke on your machine to reach
each station.
As
we said above, there is a down side.
When this tool block is used there is limited clearance
between the tools. For
large diameter parts there is insufficient space between the tools
to perform each operation. We
generally machine parts under 2.00” in diameter, so for us, this
is not a problem. We set
all three tools to a common Z axis plane and then jump from tool to
tool very quickly.
Call-out
of the tools takes a bit of work.
I use the standard tool geometry shift to activate the center
tool (which is on-center in the original tool station).
The two side tools are programmed using a G50 tool shift.
This G50 method harks back to the good old days but it still
works very well.
You
will have to allow for external coolant flow to each tool but you do
this for most tools anyway.
The
greatest advantage is in reduced idle time.
For a series of operations like drilling and tapping, this
can be quite a time saver. It
can definitely make older CNC lathes more competitive on production
work.
Adopting
this type of gang-style tooling on
a turret may not be a new idea but it is worth re-visiting for a
cost effective, competitive edge.
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