The History of Jaw Lock Mountings

Sometimes we take for granted the Jaw Lock Mountings for Top Jaws.  Simon Fairman patented the Scroll Chuck in 1840. His son-in-law  Austin F. Cushman then started Cushman Inc. and started selling manual chucks with Tongue and Groove Jaw Lock Mountings. Manual chucks are still very popular and we still sell a lot of Top Jaws with Tongue and Groove Mountings.

In the 40’s Cushman then came out with a Power Chuck with an ACME Key Mount. They are two styles of Key Mounts, ACME and Square. The ACME top jaws were our most popular Top Jaw with the
height of sales during the oil boom in the 70’s.

The Japanese Power Chucks starting coming on the New CNC Lathes in the late 70’s with fine serrations, 1.5mm x 60. Because of the length of the serrations, it gives the machinist more flexibility with the mounts. The 1.5mm x 60 is now by far the most popular Top Jaw Style. The European Chucks also went to fine serration at that time using a 1/16 x 90 and 3/32 x 90 style serration. The European’s also came out with Quick Change Chuck that takes a metric style tongue and groove.

When mounting Top Jaws a total of six screws are needed for the three jaws. Socket head cap screws are used to clamp each jaw (with a long tee nut) to the chuck’s master jaw. Before mounting the jaws the mounting on the chuck and the jaws needs to be cleaned. If debris gets in between the jaw and the chuck it can cause the chuck to be off balance and the jaws will not repeat. This will cause the parts to have run out.

When ordering Top Jaws it’s important that you have the Chuck Make and Model number. This will ensure that the right Mounting Style for your chuck. We have been making Top jaws for over 70 years so we have a very extensive library of Top Jaws. But if for some reason we don’t we can make the Top Jaw from the dimensions you provide us. So as you can see Top Jaw mounts have come a long way but still have remained the same.

Alan Garey
Huron Machine Products

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