8 Design Choices That Cut CNC Machining Cost Without Losing Precision

After 13 years in this trade and thousands of quotes, I can usually tell which drawings were drawn with machining in mind and which were drawn on screen only. The difference often shows up as a 20 to 40 percent price gap for the same function. These are the eight choices that move the number most.

1. Open Internal Corners to a Standard Radius

Internal corner radii smaller than a standard end-mill radius force special tooling or slow EDM work. A 6 mm floor radius instead of 3 mm often removes an operation entirely.

2. Respect Depth-to-Width in Pockets

Pockets deeper than 4x the tool width need slender tools, light passes, and long cycle times. If a deep pocket exists for weight only, ask whether ribbed construction reaches the same mass at half the depth.

3. Loosen Tolerances Where Geometry Is Stable

Keep plus or minus 0.005 mm class tolerances on features that need them, and give the rest standard plus or minus 0.05 mm. A drawing where every dimension is critical actually slows inspection more than machining, and inspection time is priced in.

4. Specify Finish Where It Counts

Ra 0.4 on every surface multiplies polishing and inspection cost. Reserve fine finishes for sealing faces and bearing surfaces. On most aluminum housings, as-milled finish is structurally fine.

5. Standardize Threads and Depths

Threads deeper than 3x diameter buy little clamping strength but cost tapping time and tap breakage risk. Blind-hole threads that stop 2 pitches short of full depth drill and tap much faster.

6. Design Access for the Tool

Cross-features that no standard tool can reach mean custom tooling or EDM. A five-minute check with your supplier's capability page (see our milling and turning pages) catches most of these before quoting.

7. Relax Cosmetic Callouts on Non-Visible Faces

Burr, blend, and appearance callouts on internal faces slow deburring dramatically. Cosmetic requirements belong where a person will actually see.

8. Let the Supplier Choose Process and Stock

Specifying "from 7075 plate" when a near-net extrusion or a different alloy does the job locks in waste. Tell us the function, load, and environment, and let process planning pick the cheapest route that meets it. Our material guides (aluminum, titanium) cover the common trade-offs.

The Pattern Behind the List

Every item above does the same thing: it removes a constraint the design does not actually need. Send us your drawing before it is final if you can. A 24-hour DFM pass at quoting is cheaper than a redesign after tooling.