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Simplifying the task of jaw placement on three-jaw chucks

See our PRODUCT page for more information about the Laser Jaw Setter.

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 made.

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 chuck.

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 machining.

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

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 mounted.

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 chuck.

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.

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.

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).

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 jaw.

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.)

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