5 Machining Design Mistakes That Kill Your Budget

When it comes to CNC machining, smart design decisions are just as critical as material or machine selection. Overlooked details can lead to extended machining times, wasted materials, and unnecessary costs. Here are five common machining design mistakes that silently drain your budget — and how to avoid them.

1. Tight Tolerances Everywhere

Specifying tight tolerances (e.g., ±0.001”) where they aren’t needed increases inspection requirements and slows down machining. Only apply tight tolerances to critical features; let standard tolerances handle the rest.

Tip: Default to ISO 2768 or ASME Y14.5 for non-critical dimensions.

2. Deep, Narrow Cavities

Long, thin pockets are tough to machine. They require smaller tools, multiple passes, and slower speeds — all of which drive up cycle time and tool wear.

Tip: If your design needs deep cavities, add generous corner radii and reduce depth-to-width ratios where possible.

3. Unnecessary Undercuts

Undercuts require specialized tooling or multi-axis machining, which increases cost. Designers sometimes add them for aesthetics or due to legacy designs without considering manufacturability.

Tip: Eliminate undercuts unless functionally required, or replace with standard grooves.

4. Non-Standard Hole Sizes

Custom or off-nominal hole sizes may require reamers, special drills, or multiple tool changes, all of which add cost.

Tip: Stick to standard drill sizes and tap sizes whenever possible.

5. Ignoring Tool Access

Features that are difficult for tools to reach — like hidden faces or small internal fillets — often require expensive multi-axis machines or manual finishing.

Tip: Design with 3-axis machining in mind first. Add complexity only when absolutely necessary.

Final Thoughts

Optimizing your design for manufacturability (DFM) doesn’t just reduce cost — it improves lead time, quality, and reliability. Collaborate with your machinist early in the design process to catch these issues before they hit production. Here at Ashbrook we are your go to for DFM!