A Prime Part
Another part that illustrates Northern Precision’s approach to complexity and quality is a component for a vending machine’s software-controlled lock. It was made from ¾”-dia., 303 stainless steel bar stock. Jarvis said producing the part on conventional machines would have required a minimum of five setups for turning, milling and broaching operations. Northern Precision made the part on one machine, in 15 operations, employing 13 different tools. Machining it completely took 3 minutes. Programming the most recent version of the part consumed 6 hours, and machine setup took 2 to 3 hours more.
The part had many challenging features, which Northern Precision handled in innovative ways. Three broaching operations, including an internal one performed 1″ inside the part, were accomplished with specials. “The broaching operations were similar to shaping,” Jarvis said. “The repetitive motions were accomplished through parametric programming.”
To finish a large slot and produce a spherical chamfer on a broached feature, Northern Precision employed a dual right-angle drill head, mounted in a live cross-tool position. The head had a ballnose endmill on one side and a stub-length, square-shoulder endmill on the other. The arrangement provided the off-center end-working capability needed to square off the slot with the part in the main spindle, and then, on the back spindle, produce the chamfer on the part’s other end.
Cross-holes in the part had to meet a ±0.0005″ tolerance, but the machine lacked enough live-tooling stations to mount a reamer. The solution was to program a small endmill, already used for another part feature, to circular-interpolate the hole to the required size.
‘It Can Be Done’
Jarvis contrasted today’s Swiss machines with the screw machines he worked with years ago. “These new machines are great. The accuracy is amazing,” he said. “To change a dimension on a screw machine, you had to physically move a stop. On these [Swiss machines], you just punch in how much you want to move it and it moves.”
What does apply from his screw machine days, however, is a can-do attitude. Jarvis said, “We’ve worked with older fellows who really came up with some neat ideas. They had a philosophy of ‘It can be done; you just have to find a way to do it.’ It’s what pushes us.”
Northern Precision Inc. can be reached at (513) 860-4701.