April/May 2026 www.pwemag.co.uk Plant & Works Engineering | 9 Advertorial Precision in close-tolerance part design results from aligned decisions across design, materials science, and manufacturing. A single misstep in any area can cascade into scrap, rework, and cost overruns. Design for manufacturability connects those decisions and keeps production viable. This guide draws on the expertise of Fisher Barton, a Watertown, Wisconsin-based manufacturing group with over 100 years of experience producing complex components for OEMs and industrial manufacturers worldwide. The aim is to help companies improve their accuracy during production and create topquality products. Foundational Principles of CloseTolerance Part Design Design success begins long before a spindle turns. Engineers who overspecify tolerances on nonfunctional features drive up machining time and cost without improving part performance. Tolerance stack-up analysis addresses this directly by mapping how individual dimensional variations accumulate across an assembly. It reveals which features genuinely require micronlevel precision. A study confirmed that systematic tolerance optimisation delivers significant cost reductions over equal-tolerance allocation. Prioritise critical mating surfaces, and relax specifications everywhere else. Material selection runs in parallel with the tolerance strategy. An item’s coefficient of thermal expansion, machinability, and stressrelief behaviour all influence whether a part holds its dimensions through a full production run. Engineers who select alloys based only on end-use mechanical requirements often find that material expands unpredictably under machining heat. Evaluating dimensional stability from the outset eliminates an entire category of downstream failure. Optimising the Manufacturing Environment for Precision The physical environment where machining takes place directly affects dimensional outcomes, even when the equipment and tooling are fully capable. Maintaining Thermal Stability Heat is the primary cause of dimensional inconsistency in close-tolerance machining. A small temperature rise can push a precision steel part beyond tolerance limits in highaccuracy applications. The international standard measurement temperature is 20° Celsius (68° Fahrenheit), and leading precision manufacturers hold their environments as close to that benchmark as possible. Ensuring Machine and Tool Integrity A stable environment delivers diminishing returns if the machines within it aren’t calibrated daily. CMMs, CNC machining centres, and precision grinding equipment all develop measurement and positioning drift over time. Rigid workholding fixtures that distribute clamping forces evenly are equally important. Even a few microns of part movement under cutting forces will produce parts that are consistently out of specification, with no obvious cause visible to the operator. Integrating Material Science Into Design True design for manufacturability accounts for how materials behave under heat and stress. This is where a knowledgeable partner delivers true value. Fisher Barton’s material-sciencebacked approach addresses the three challenges that frequently drive up cost and scrap in close-tolerance work: High manufacturing costs: Unnecessary complexity and overtoleranced surfaces increase cost at every machining step. Early collaboration helps to identify design adjustments that simplify machining paths or to substitute a more cost-effective yet equally stable material. Scrap reduction manufacturing: Scrap follows predictable patterns tied to material behaviour under stress and thermal response during extended runs. Fisher Barton’s expertise structures the machining sequence to account for these patterns. Complex close-tolerance part design: Many manufacturers decline projects because the combination of material, tolerance, and form exceeds what a generalist shop can reliably produce. Fisher Barton’s depth of material knowledge allows the team to take on these projects and build a production path that makes them repeatable and efficient. Advanced Machining and Quality Control Execution is a process discipline when working with a well-engineered design. Dedicated roughing tools remove bulk material quickly, while separate finishing tools preserve edge geometry and surface quality on final passes. In-process metrology using CMMs and laser scanners catches dimensional deviations as they develop, rather than after an entire run is compromised. Investing in Precision Pays Off Achieving close-tolerance accuracy benefits organisations that address it systematically. This compounding effect ensures batch conformance, sustained scrap reduction, decreased rework, and stronger long-term supplier relationships. https://www.fisherbarton.com/capabilities /close-tolerance-machining/ The Practical Guide to Achieving Accuracy in Close-Tolerance Engineering
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