Some time ago we were asked to repair a vintage Westrex 2B feedback cutter head.
As with all Western Electric and Westrex products, their cutter heads were beautifully made and represented the state of the art in their time. Not only did they sound great, they also looked aesthetically pleasing, with curved lines that were not a trivial task to manufacture, in the days before CNC machine tools, CAD software and pocket calculators!
Presto 1-D and 1-C cutter heads are frequently encountered on our lab bench for repair and restoration. Some are just regular repairs to original spec, others are rewound to a different impedance, but some undergo more comprehensive and exciting modifications!
We have previously examined modifications where a feedback system was added to a Neumann MS-52H and an Audax R-56 cutter head. This time, we shall discuss adding feedback to a Presto 1-D, which arrived with damaged coils.
This Audax cutter head arrived with a fried coil and a completely crusted armature. The damping material had not aged well.
A complete disassembly, cleanup and reassembly would be required, with the renewal of the damping material and drive coil. This was yet another perfect candidate for our feedback modification.
All Hardinge HLV and HLV-H variants feature a continuously variable speed drive to the spindle. It starts with a 3-phase, two speed squirrel cage induction motor, rated at 500 rpm and 1500 rpm nominal (less in practice, due to slip) at 50 Hz. This would be 600 rpm and 1800 rpm at 60 Hz.
Finding a Hardinge HLV can be challenging enough, especially if, like us, you happen to be located in Europe. At 1400 lbs, shipping and handling gets complicated. In a previous post, we described the joys of forklifting the beast onto a platform trolley (with suitable structural support added to the building), to get it to the workshop, though narrow corridors and doorways. Once there, it had to be lifted off the trolley and placed directly on the floor. With no chance of being able to drive the period-correct forklift truck into the shop, we had to get creative. A hydraulic engine hoist along with slings and tacks got the job done neatly. With the lathe on the floor and properly leveled, it was time to check it over, replacing, adjusting, lubricating and cleaning parts along the way!
It consists of a Rek-O-Kut Model V 16" turntable, which he found in the USA (where else?) as a non-runner. The motor was in bad shape and refused to run at all. Even if it would run, it was expecting to be fed on a regular diet of 110 VAC/60 Hz!
A simple yet effective movement which has seen many decades of regular use, appears under the lid of this dial indicator.
It was once able to indicate accurately in 0.01 mm graduations, through a gear train driven by a rack on one side of the spindle.