8 DFM Callouts That Quietly Raise Your CNC Cost

By The Vrocure Team · 2026-06-24 · 8 min read

Design for manufacturability (DFM) is the practice of designing a part so it is straightforward — and therefore cheap — to make. Most cost is locked in at the drawing stage, long before a single chip is cut. Learn to spot these eight callouts and you can shave real money off a part without changing what it does.

1. Tolerances tighter than the function needs

A general tolerance of ±0.1 mm is cheap; ±0.01 mm is not. Tight tolerances mean slower feeds, more passes, better fixturing, and inspection on every part. Reserve them for mating features and let everything else run to a standard block tolerance.

2. Thin walls

Walls thinner than about 0.8 mm in metal (1.5 mm in plastic) chatter and deflect under tool pressure. The shop compensates with light cuts and extra support, which is slow. If a wall must be thin, add a rib or radius to stiffen it.

3. Sharp internal corners

A milling cutter is round, so it physically cannot cut a sharp internal corner. Specifying one forces EDM or a tiny tool taking tiny cuts. Add an internal radius of at least the tool radius — a corner relief costs pennies and saves an operation.

4. Deep pockets and tall ribs

Once a pocket is deeper than about 3–4× the tool diameter, the tool starts to flex and the finish suffers. Deep features need long tools, slow feeds, and sometimes a second setup. Keep depth-to-width sensible or split the geometry.

5. Small holes in deep bores

A high aspect-ratio hole (deep relative to its diameter) needs a peck-drilling cycle to clear chips and a special long drill. Where you can, open the hole diameter or reduce depth to keep it inside a standard drill’s reach.

6. Fine surface finishes everywhere

A mirror finish is an extra finishing pass — sometimes a whole secondary process. Specify a fine Ra only on sealing or sliding faces; an as-machined finish is free and perfectly good for the rest of the part.

7. Too many setups

Every time the part has to be unclamped and re-fixtured to reach a new face, you pay for setup and risk a tolerance stack between faces. Designing features onto fewer faces — or accepting a 3-axis-friendly layout — cuts both cost and error.

8. Exotic materials without a reason

Titanium and hardened tool steels are expensive to buy and slow to cut, wearing tooling fast. If the application does not demand it, a free-machining aluminium or steel will be a fraction of the cost and time.

The DFM mindset

None of these callouts are wrong — they are choices. The point of DFM is to make each choice on purpose. Ask of every tight tolerance, thin wall, and fine finish: does the part’s job actually require this? When the answer is no, you have just found free money. When the answer is yes, you have a defensible reason the next time a supplier asks why the quote came back high.