From the time of earliest beginnings in 1985 in the town of South Beloit, Illinois to today, a lot of changes have occurred in double disk grinders. The advancements parallel changes at J.L. Lucas, a company that began rebuilding Jack Shaft machines in the early 1900s and now remanufactures grinders with technologies that were not even concepts then. The progress has been monumental. The contrast is dramatic when a late 1920's disc grinder, like the one on display in our office, is compared with grinders shops today. From top to bottom the original features of the old double disc grinder have been improved and enhanced. Yet as a tribute to its inventor, Mr. Frederick Gardner, the original concept is unchanged. As in its beginnings, nothing compares with the productivity of double disc grinder for making parts that require flat, parallel surfaces. The double disc grinder is the perfect candidate for remanufacturing and updating with new controls. Initially most machine tools gained much of their accuracy from sheer mass of their structure, and double disc grinders were no exception. The mass of yesterday's machines provides a solid base for remanufacturing using today's methods and materials. The heart of the double disc grinders is its rugged base. After total dismantling of the grinder, the base is where remanufacturing begins. The base is inspected for structural integrity because the base must resist the sever grinding pressures generated between the two opposing grinding wheels, which in many applications are semi-free floating parts of the machine. The base must also maintain the critical alignment of the two opposed wheelheads, the dressing and truing systems, and the tooling knee. On most grinders, these have only the base as a common connection. As remanufacturing begins, the base is machined, scraped and spotted to new machine tolerances. The lubrication system lines are inspected and checked for full operation. Hydraulic systems lines, which also run through the base, are cleaned and checked.

Next, the wheel feed system comes under consideration. The actual application and the piece parts dimensional requirements will determine whether an Acme Type or Precision Ground ball screw with a preloaded nut is selected for infeeding the spindle housing. The system must be capable of moving as little as 0.000010 inch at the control system's or operator's precise direction while being subjected to grinding forces. In most grinders, the wheel head system includes the spindle and spindle housing, which must be inspected for structural integrity and checked for size and roundness in the bearing surface areas. If the spindle area is worn, it is ground undersize, plated with a hard chrome or plasma sprayed with metal. The rebuilt surface is then reground to the original specification. Controlling the tolerances for bearing fit makes the application of a more precision class of bearing possible, and the accuracy of the new spindle will exceed that of the original machine.

Having rebuilt the spindle assembly and placed it in a precise wheelfeed system on the heavy, rugged base, the basic core of the disc grinder is completed. Consideration must be given to wheel truing and workpiece tooling, which are subassemblies on the base machine.

Dressing and truing are important factors in the performance of the double disc grinder. Dresser arms that arc across the wheel face have a shaft and bearing as the pivot point, which must be inspected and brought to original conditions. Machines with bar type dressers must be remachined and fitted to the mating housing. Accurate repeatable truing of the grinding wheel requires rigid mounting to the base in a manner that maintains the dresser's alignment to the wheelhead slides.

The final mechanical considerations are the tooling knee and the components that will actually provide the workpiece motion between or through the grinding wheels. These can consist of a feed through assembly with opposed belts, rollers or chain pickoff. Another common tooling arrangement is a rotary carrier system. The accuracy of the rotary and feed thru systems on a free floating part are dependant on the entrance and exist side guides that align the workpiece prior to contact with grinding wheels. Improper placement and alignment of these guides will reduce the tolerance holding capability of the grinder and will cause excessive wheel truing. The side guides are operator adjustable and mute be capable of moving inward and outward accurately, adjusting for different parts and or part thicknesses. A rotary carrier application in which the part is clamped in the rotary dial requires special care in remanufacturing of the carrier drive system. Run out of the rotary carrier drive hub should be within 0.0001 inch or better to ensure accuracy.

The third most common tooling assembly is the reciprocating method which produces the closest tolerance and can be used for large parts that are individually ground. This tooling assembly is critical to producing close tolerances. The part Carrier reciprocates between the two opposed advancing wheel heads and must be rigidly mounted to the base. The slide assembly that provides this reciprocation must be remachined and realigned to the machine wheel heads to ensure precise repeatable performance.

At this point we have a disc grinder remanufactured to state-of-the-art technology standards that can take advantage of today's electronics and controls. With the application of solid state controls, PLS and servo motors, tolerance holding capabilities are remarkable, with the serviceability and reliability of a home computer. Installation of an operator's touch screen eliminated most or all push buttons while providing, at a glance, exact grinding head position and status of the machine cycle along with diagnostics. Programs can be established that allow the operator key pad input of all or selected machine functions. Additional options include variable speed spindle motor controls, servo controlled dress cycles and setups, and statistical closed loop gauging systems that control part size by generating and continuously monitoring a control chart, this automatically controlling size to its best CPK.

Prior to final painting and shipping to the customer, the grinder is run off to the customer SPC and CPK requirements while grinding the customer's parts. With his remanufactured machine, the customer has gained a manufacturing edge in his operation at a cost less that one half of a new machine in most cases, or has turned an older marginally adequate machine into a productive, close-tolerance-holding double disc grinding system.

My hat's off the Mr. Gardner. I just wonder how he would respond to the question of whether double disc grinding is an art or a science?

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