Modern Machine Shop

DEC 2018

Modern Machine Shop is focused on all aspects of metalworking technology - Providing the new product technologies; process solutions; supplier listings; business management; networking; and event information that companies need to be competitive.

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Modern Machine Shop 65 Fixture Design components with complex geometries are all dif- ferent, but many of the same principles and strate- gies apply. Here are a few examples: START FRESH. 'Engineering and design assistance is a key value-add for Contour Precision. Ideally, the shop can get involved early enough to choose the starting point for machining, which typically becomes the reference datum against which all critical features are measured. "We just quoted a job that called for holding a rather large machin- ing feature true to a really tiny surface, and that's not a good way of designing things," Mr. Whitt says. "We'll try to work with the customer on the GD&T (geometric dimensioning and tolerancing) Andy Marchand, CNC setup operator, sets up a component for a cast assembly on one pallet while another part is being machined on one of the shop's horizontal machining centers, which have more automated capability than the five-axis models. Here is a closer look at the fixture in the previous picture. It is configured in this way because clamping over the flange edge would result in machining away part of the fixture. for that one." Given variations in the casting or forging process, the starting point should also have enough stock for initial machining to ensure an even, consistent surface from part to part. MAKE TIME FOR TROUBLESHOOTING. For many jobs, the shop does not get a chance to provide design assistance. Mr. Whitt and Mr. Kerecz say it is common for gates, risers and other features of casting and forging molds to be placed with little regard for later machining of the components that emerge from the tooling. All leave extra material behind, and machinists might not know exactly where until the workpiece is in hand. What's more, results can vary from part to part "Usually, holding looser will give you the better-quality part." — Mike Kerecz, engineering manager

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