Manth-Brownell (Kirkville, New York) is one of the largest manufacturers of turned parts in North America. The company has been devoted to the screw machine industry for more than 46 years. It has more than 146 machines in house and is an ISO 9002 and QS 9000 registered company.
Manth-Brownell needed an affordable solution for an internal grip on the pickoff spindle of its EuroTurn 6/32 six-spindle screw machine (32 mm through capacity). The job called for a brass turned part with thread milling. The company needed to backwork the part, but it couldn’t grab the outside of the part with the OD pickoff attachment because it would distort the threads.
One solution to this dilemma would be to buy the ID pickoff attachment from the machine tool builder. It would cost $36,000, and Manth-Brownell would have to purchase a $7,650 kit to downsize from 42 mm to the existing 32 mm size. The setup time involved would be about 8 hours.
Wes Skinner, president of Manth-Brownell, had no idea how long the job would last, or how soon he would have another job with ID chucking to substantiate the purchase. Mr. Skinner says that he could have moved the part to another machine for the second operation, but he knew there had to be a more productive solution. He attended a regional PMPA meeting the same day he was contemplating the issue and ran into Cal Macomber, the director of sales and marketing at Hardinge Inc., and Neal Des Ruisseaux, manager of workholding engineering at Hardinge, whom he’d been doing business with for 40 years. They put their heads together, jotting notes and drawings on napkins.
Hardinge engineered an exclusive expanding collet to fit the machine’s existing OD pickoff attachment. Changeover from a standard OD gripping setup to an ID setup would be a matter of changing just the collet, rather than changing the entire attachment. The expanding collet would cost much less than purchasing the ID attachment and offered additional savings in setup reduction. Installing the Hardinge collet would take less than 15 minutes to insert the collet, set it up and get the position for proper ejection and clearance. The built-in spring ejector provides automated parts removal for faster throughput. This newly developed collet fits Euroturn OD pickoff spindles, as well as Gildemeister and Tornos Deco machines, and it can be made to hold workpieces of a specific size and/or shape.
Manth-Brownell was able to make a comparison between the Hardinge collet assembly and an ID pickoff attachment that was on loan to the company. Aside from the setup time and cost savings, the company reports that with the Hardinge expanding collet, there is little problem holding tolerances on machined features as the machine goes from a cold start to normal operating temperature. In fact, Manth-Brownell found improved length control—the part easily maintained a 0.0002 to 0.0003-inch tolerance, as compared to 0.004 to 0.006 inch with the ID pickoff attachment. Mr. Skinner attributes the collet’s indifference to temperature to its design and the fact that there is less friction than would be present in a larger assembly.
Manth-Brownell is currently running this part ten shifts per week. The shop produced 1 million parts using the first expanding collet prototype furnished by Hardinge, and another 750,000 parts have been made with a second collet, without any problems. James Wilsey, Manth-Brownell’s machine operator and setup person, anticipated some chip-buildup problems, but Hardinge designed openings around the assembly that facilitate flushing of the chips. Mr. Wilsey uses shop air to blow out the collet once in a while, but the shop has never had to take the collet assembly apart to clear any chips.