Disclaimer: CNC Concepts, Inc. accepts no responsibility for the use
or misuse of techniques shown in this web page. We simply publish information
we feel will be of interest to CNC users. In all cases, the reader is totally
responsible for considering the implications, good and bad, of implementing one
or more of the techniques we show.
Simplifying the task of jaw placement on three-jaw chucks
Most three-jaw chucks used on turning centers have a series of fine
serrations on master jaws and top tooling that must be properly aligned when
top tooling is mounted to the chuck. But by the nature of three-jaw chucks
(jaws are 120 degrees apart), it can be difficult - if not impossible - to
determine the exact diameter at which each jaw is being placed in the chuck.
In addition, the fine serrations of the master jaw and top tooling make it
very difficult to align all three jaws in the same series of serrations. Most
setup people count the number of serrations on the master jaw in order to get
each jaw into the correct serration. But time-consuming mistakes are often
If jaws are not properly aligned, of course, they will not run true when the
spindle is started. Fortunately, this will be very obvious to the setup person.
But the jaws must be removed and the entire task of jaw placement must be
repeated. It is not uncommon for entry-level setup people to make several
attempts before jaws are properly aligned and at the correct diameter in the
Some chucks have concentric circles scribed on the chuck face to help - but
even with these chucks, jaw placement can be time consuming, error prone, and
difficult - especially for entry-level setup people.
Jaw placement time directly affects setup time. The CNC turning center must,
of course, be down while jaws are being mounted to the chuck. Anything you do
to reduce jaw mounting time will, in turn, reduce setup time.
What about the chucking plug or ring?
After correct mounting to the chuck, soft jaws must often be turned or
bored. The chuck must be activated (opened or closed), and the jaws must be
clamped on a chucking plug or ring. Most chuck manufacturers recommend that
this clamping take place about half way through the chuck jaw's stroke. And
clamping pressure should be set the same as it will be for production
Even determining what diameter plug or ring must be used can be difficult.
Again, the jaws on three-jaw chucks are mounted 120 degrees apart, making it
impossible to use standard measuring tools (scales, calipers, etc.) to
determine the diameter at which jaws will be clamped half-way through their
stroke (unless pie-jaws are being used). Most setup people use trial-and-error
to find the correct diameter chucking plug or ring. While experience setup
people may often do so on the first try, entry-level setup people may require
several time-consuming attempts.
One great solution
These three problems - properly aligning all three jaws, getting them at the
proper diameter, and determining what diameter chucking plug or ring must be
used - are all easily solved with a new product manufactured by CNC Consulting
and Training and now distributed by CNC Concepts, Inc. The
Laser Jaw Setter (patent
applied for). With the Laser Jaw Setter, your setup people will know in which
serration each jaw should be mounted, the diameter at which the jaws will be,
and they'll be able to easily determine the diameter of the chucking plug or
ring needed for machining soft jaws. And of course, these three improvements
reduce the time needed to mount and machine jaws -simplifying the task along
the way. The obvious result is reduced setup time.
How it works
Click image to enlarge.
The Laser Jaw Setter incorporates a laser pointer which will be used to
point at the master jaw serration of each master jaw in which the jaws will be
Click image to enlarge.
First, a magnetic base (not supplied) is placed on the turret face. This is
the same kind of magnetic base used to hold dial indicators. The Laser Jaw
Setter is placed on the bar of the magnetic base and secured in such a way that
it is pointing toward the chuck face.
Second, a push-button is pressed to activate the laser within the Laser Jaw
Setter. Much like any laser pointer, the beam generated by the Laser Jaw Setter
will remain very small, and will act as a pointer to the master jaws on the
Click image to
Third, the turret will be moved in X so that the center of the laser beam is
brought to a known diameter. If the chuck has a through-hole, for example, the
laser beam will be brought to the diameter of this hole.
Click image to enlarge.
Fourth, the X axis display on the position display screen will be set to the
known diameter. From this point, as the setup person moves the X axis, the X
axis display will constantly show the current diameter of the laser beam.
image to enlarge.
Fifth, the setup person will move the laser beam to the diameter at which
they want to mount jaws. Say, for example, they are mounting soft jaws to hold
on the outside diameter of a workpiece, and they know that the very end of each
jaw must be about 0.25 smaller (on the side) than the diameter of the jaw they
need to bore. If they will be boring to a diameter of 3.5, they will set the
laser pointer to a 3.0 inch diameter (again, this is easy to do by monitoring
the X axis position display).
Click image to
Sixth, with the laser beam pointing at the appropriate diameter, they will
rotate the chuck (by hand) until a master jaw is targeted by the beam and mount
the jaw so that the end of the jaw is aligned with the laser beam. This process
will be repeated for each jaw. During this process, the setup person can rest
assured that all three jaws will be placed in the same serration of the master
Seventh, the setup person can easily determine the diameter of the chucking
plug or ring needed for soft jaw machining as long as they know the jaw stroke.
If the jaw stroke is 0.5 inches for example, they will need a 2.5 diameter
chucking plug to bore the jaws in our example.
What will you save?
While it's difficult to predict the amount of time savings you'll experience
(skill level of setup people vary dramatically), you should agree that it will
be substantial. To be more precise, watch your own setup people. How long is it
taking them to get jaws mounted and properly aligned? Using the
Laser Jaw Setter, it will
take an average setup person less than three minutes! (We're assuming that jaws
have been removed from the previous setup and keys have been mounted in the
jaws prior to starting this procedure.)
Additionally, since we're simplifying the task of jaw placement, a person
with lesser skill will be able to proficiently accomplish the task on the first
try - time and time again.
If you're having problems visualizing how the Laser Jaw Setter works,
watch this video
that shows the entire process! (Video is formatted for Windows Media Player.)