The Gleason Curvic Coupling

Warner and Swasey's engineering strength and progressive machine design was found in many ways during its long history. One of these important design aspects can be found in many of the SC, bed type machines from their early history. That was the use of the curvic coupling for the turrets of those machines. This feature assured index accuracy and proper alignment with spindle nose and bed centerline 100%. This accuracy was achieved through the unique and patented design of the curvic coupling on the bottom of the turret and its mesh with the top of the carriage.

In essence, the curvic coupling was a ring of precision ground face splines which were meshed after index. The splines, or radial teeth, were ground in such a manner that on one member the sides of the teeth surfaces that meshed were convex and on the other member the sides were concave. The result was that after these members were clamped together, perfect index location was achieved, and further, the turret was perfectly on center.

Other, less expensive solutions were used by our competitors. The Hirth coupling, and various other "face gear" versions were used, but none of those alternatives worked as well as the W/S solution, featuring the Gleason curvic coupling. As I recall, we had at least two grinders kept busy in the production of these curvic couplings.

The other important advantage of the curvic coupling was that its accuracy in both axes actually improved with use, rather than being degraded. The only "trick" in their application was the necessity of guarding against the entry of chips or other debris into the seating area, W/S handled that part of their design very well also.

Thank you for this very interesting description of this piece of machine tool design. I think this is a good illustration of how in the history of technology important advances are often of this sort- a better way of doing something that's already been done. In this case indexing a turret with greater accuracy and by a mechanism that even got better with use.
David

American Tool Works also had curvic couplings under their turrets in the early 60's. They featured a quick change turret you could have the tools preset in and left set up if you wished while you used another turret. They sold a square and hex turret that were instantly interchangalbe. American started off buying couplings from Gleason but early on bought a government surplus coupling grinder dirt cheap that may have never been used. To make a set of curvic couplings you had to have a master set to gage with.
I don't know the first use of curvic couplings but General Electric jet engines had one between each compressor disk. I first saw them on the J-35 and J-47 and they were still in use on the J-79 and J-93. GE compressors did not have a through shaft. The first and last disk had a stub shaft on one side. The compressor rotor was a stack of disks aligned by the curvic couplings and held together with several through bolts, all designed to save the weight of a through shaft.
On a turret a curvic coupling was a great improvement over shot bolts as they were prone to stick. I do know of two sets of curvic couplings that were disolved by nasty coolant getting in the turret.

John - you are absolutely correct and I probably should have mentioned the fact that it was for jet engine applications that the curvic coupling design was developed, and that Gleason got involved with at the onset, by the development of their grinder.