Toolholder Improves Surface Finish

Rapidac Machine, a Rochester, New York, contract manufacturer of molding and process equipment for the plastics industry, found itself in a difficult situation attempting to machine a mold from H13 tool steel with a Rockwell C hardness of 56 plus. The customer specified the original mold was to be machined from hardened material so as to be assured the technology was developed for two reconditions of the mold, allowed for in the mold design.

Columns From: 8/1/2001 Modern Machine Shop,

Rapidac Machine, a Rochester, New York, contract manufacturer of molding and process equipment for the plastics industry, found itself in a difficult situation attempting to machine a mold from H13 tool steel with a Rockwell C hardness of 56 plus. The customer specified the original mold was to be machined from hardened material so as to be assured the technology was developed for two reconditions of the mold, allowed for in the mold design.

Chuck Day, general manager of Rapidac, called in Tom Schaefer of Harrison Industrial Supply for his recommendations of cutting tools capable of effectively machining hardened H13. Mr. Day had already tried several manufacturers of cutting tools but was impressed with the Harroun Enterprises tooling that Mr. Schaefer recommended. The Harroun tooling provided the highest metal removal rates and the longest tool life. The remaining obstacle to overcome was surface finish.

Mr. Day went back to Mr. Schaefer and requested his recommendations for improving surface finish without a reduction in tool life or material removal. Mr. Schaefer had recently attended a seminar put on by Richmill USA (Santa Fe Springs, California) on its new High Bred Toolholder. Based upon the data presented at the seminar, he felt this was a good opportunity for Rapidac to test the new High Bred simultaneous face and taper contact design.

Conventional taper shank toolholders fit into the spindle of a CNC milling machine with taper-to-taper contact. Ideally the amount of contact is 95 percent plus, with any mismatch in the small end of the taper. The toolholder is positioned in the spindle with an automatic tool change arm and secured in the spindle with spring pressure furnished through a stack up of Bellville Washers in the center of the spindle. The Richmill toolholder has this same taper-to-taper contact and a pressurized contact with the face of the spindle. Until now, to have dual contact with the taper and spindle face required HSK or custom designed spindles. The Richmill design adapts to any standard 40 or 50 taper spindle. The simultaneous taper and face contact is said to increase the rigidity of the connection between toolholder and spindle by more than 30 percent.

Mr. Day measured the surface finish of his mold prior to using the Richmill holder. The Harroun HIBF cutting tool was yielding a surface finish of 36 microns with acceptable tool life and material removal rates. Once the Harroun ball mill was installed and run in the new toolholder, the surface finish was improved to 24 microns. A minimal amount of hand polishing took the mold to customer specifications. Additionally, tool life was increased from 4 hours to 6 hours per edge.

Mr. Day commented that at first he was concerned the balance design and toolholder design caused a longer tool projection than normal. Once he inspected the surface finish and saw the reduction, he was confident the new design would perform as advertised.

Richmill USA is a subsidiary of Richmill Manufacture Ltd. of Osaka, Japan. Richmill has been supplying workholding and toolholding solutions to automotive manufacturers for more than 40 years.

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