Production Machining

AUG 2018

Production Machining - Your access to the precision machining industrial buyer.

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Page 39 of 91

:: Figure 2: Two pins: This setup provides accurate part loca- tion, assurance that the part will not move regardless of how hard an operator cuts, and it provides full access to five sides of a prismatic workpiece. The part shown is a cast-iron guide sleeve for a can-making machine. It is critical that the sleeve bore is accurate (perfectly round), and it must also exactly reference on three sides for X, Y and Z axes. Basically, if it is held in a vice, the clamping pressure will ensure that the finished part fails inspection on hole accuracy/roundness. If the part is re-chucked to get clear access to the three critical sides, it again most likely fails on the basis of referencing the hole to the three sides. Considering that the part is cast iron—lower magnetic holding force—and not large, relying solely on the magnet is not possible. The solution was to machine the top face—completely non-critical in the final part—by holding it in a vise. In this face, two precision pin holes were added for a subse- quent operation location. For the second operation, the part is held on a high power magnetic chuck with a grid plate that includes two precision pins to engage the op. 10 finished face. The part is now positively located and held in a stress-free state with no clamp- ing distortion. The machining is complete on a five-axis mill. The exposed grid plate under the part is magnetic and has gathered a nest of shavings held in place magnetically. However, the part itself is completely clear of chips. WORKHOLDING 38 PRODUCTION MACHINING :: AUGUST 2018

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