Advanced Precision Machining

Workpiece Setup: Reducing Defects Through Better Error-Proofing

[March 31, 2015] The CNC machine shop business, as with most operations in the manufacturing industry, presents challenges when it comes to turning a profit. Subject to an array of obstacles such as the recession, the loss of precision machining jobs, rising material/equipment prices, and the struggle to maintain customer relationships, many shop owners/managers question whether they can thrive in today’s economy. Improving efficiency and productivity through cost cutting methods is paramount to saying ahead. Machine shops today rely on CNC milling and machining centers to give them a competitive advantage. These technologically advanced marvels of engineering produce precision machine parts that, to the CNC machinist, are works of art. But there is a caveat; they are only as good as the human being entering inputs. Errors are commonplace in the CNC machining process, and while they can’t be completely eliminated, certain fail-safes can be implemented to ensure that they don’t result in wasted time and money.

In the setup, programing, tooling and actual high speed machining process, any missed step along the way may result in the production of a defective part, waste or worse, the comprised safety of an employee or damage to equipment. In all cases, quality, productivity and efficiency suffer. These processes can never be made error-proof, but by reducing defects through better technique, precision manufacturing facilities can lower operating costs by maximizing quality and reducing rework. With maybe the exception of accurate CNC verification and programming, the workpiece setup procedure is perhaps the important step in ensuring that specific part tolerances and accuracies are met.

With the aid of some informative tips in an article from Modern Machine Shop, we want to briefly take our readers through 4 methods of setting up a workpiece to account for any uncertainties in positioning. If attention to detail is followed, these techniques are an efficient way to achieve proper accuracy, thus eliminating lost money and time.

1.) Using Feeler Gages

Low cost and perhaps the most widely used technique, but time consuming and crude. Feeler gages are placed between the workpiece and cutting tool to measure the gap. Once measured, the CNC program can be adjusted to account for any positioning uncertainty.

2.) Using Fixtures

Fixtures are utilized to secure and accurately position the workpiece in a known and repeatable location relative to the cutting tool. Such fixtures must be custom-designed, and therefore their use is often limited to high production runs. They are not really feasible for small-batch milling and machining.

3.) Using Mechanical Touch Probes

Mechanical touch probes automatically find the position of the workpiece, relative to the cutting tool, but again, their use is somewhat limited. Typically purchased off the shelf, touch probes often lack compatibility with many CNC machining centers, and on the part to be machined, there is often a lack of suitable contact points or useful surfaces for the probes.

Before they cause problems further down the line, error-proofing the setup process is a great way to improve quality, reduce waste and eliminate unnecessary costs, and can be the difference between making a part that brings in money for your shop and generating scrap that will erode your profit margin.

“APM is dedicated to manufacturing the highest quality precision parts while providing the best customer service experience in the machine shop business”. For additional information or to request a quote, please visit or call 303-776-1910.

About the Author

Gerry Dillon is a co-founder, current owner and certified CNC machinist at Advanced Precision Machining (APM), a full-service machine shop located in Longmont, Colorado. Before making his home in the United States in 2000, Gerry was born and raised on the emerald isle of Ireland and took an interest in milling and machining from an early age, ranking #1 in the Irish National Apprenticeship Program. In 2005, he partnered with his friend and colleague, Kirk Tuesburg, currently APM’s machine shop manager, together launching what’s grown into a leading Colorado machine shop. Gerry brings over 30 years of machining experience to the shop floor, and is certified in all aspects of geometric dimensioning and tolerancing. 

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