Boring Soft Jaws


The following is an article that was published by Modern Machine Shop, and written by Mike Lynch Founder and President, CNC Concepts Inc. 

I liked it, so I thought I would share.

“For external clamping, subtract the amount of material you’ll be removing from the jaw from the diameter just determined. For example, to clamp on a 4.0-inch diameter using soft jaws, with about 0.1 inch of material to be removed from each jaw, the mounting diameter will be 3.55 inches (4.0 inches minus 0.25-inch jaw stroke minus 0.2 inch of stock—twice the amount of stock to be removed from each jaw).

Once you have determined the diameter at which the current clamping surface of each jaw must be mounted, you can make the long boring bar point to this diameter. To do so, calibrate the boring bar’s pointing diameter with the X-axis display.

With the X-axis display calibrated, use the handwheel to bring the tip of the boring bar to your calculated clamping diameter. Then bring the tip of the boring bar up close to the chuck face. Use the tip of the boring bar to determine which serration each jaw should be mounted in. You may have to move the boring bar away in Z (but do not move it in X) in order to actually mount the jaw. Repeat this procedure for each jaw. When you’re finished, each jaw will be in the same serration.

With hard jaws, the chuck will be in the middle of its stroke when the workpiece is clamped. However, if you’re mounting soft jaws, they must be machined. When you’re finished machining them, they will clamp on the workpiece in the middle of the chuck stroke.

The same technique can be applied to internal clamping, but you may have to calculate the diameter a little differently. If you’re still mounting the jaws with the master jaws toward the spindle center, you still subtract the jaw stroke from the workpiece diameter to determine the clamping diameter. So for hard jaws, the calculation is exactly the same as it is for external clamping. However, with soft jaws, you must add twice the amount of material you’ll be removing from each jaw to the diameter just calculated.”

In addition to techniques mentioned above, Haas Automation produced the following videos:

Part 1: Fundamentals and OD Gripping

In the first of a two-part installment, a Haas certified machinist explores our recommended soft-jaw cutting techniques and the proper way to cut OD gripping jaws.

Part 2: Haas certified machinist guides us through more advanced lathe soft jaw cutting techniques, including ID gripping, re-cutting, and adding a taper to your soft jaws.


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