Design for Manufacturing: 7 Principles That Cut CNC Machining Costs by 50%

By PreciseMaker Engineering Team · 8 min read · Design for Manufacturing

Most parts cost twice as much as they should. Not because of the material. Not because of the machine shop. Because of the design.

Design for Manufacturing (DFM) is the difference between a $150 bracket and a $45 bracket — made from the same aluminum, on the same machine, to the same function. Here are seven principles we apply to every project at PreciseMaker.

Loosen Tolerances Wherever You Can

Every extra decimal place in your tolerance costs money. Going from ±0.05mm to ±0.01mm can triple the machining time. Ask yourself: does this surface *actually* need to be that precise?

Rule of thumb: Only tighten tolerances on mating surfaces, bearing seats, and alignment features. Everything else: ±0.1mm or looser.

Avoid Deep Pockets with Sharp Internal Corners

End mills are round. They can't cut a sharp internal corner — they leave a radius equal to the tool radius. If your design calls for a square corner at the bottom of a deep pocket, you're forcing the shop to use a tiny tool, which means slower feeds, more tool changes, and a higher quote.

Fix: Add a relief radius at internal corners. Aim for a radius ≥ 1/3 of the pocket depth. Better yet, redesign to avoid deep pockets entirely by splitting the part or using a different manufacturing approach.

Standardize Hole Sizes

Every non-standard hole means a custom drill bit, a tool change, or a boring operation. Standard drill sizes (M3, M4, M5, M6 clearance holes, etc.) are faster, cheaper, and just as functional.

Fix: Use MISUMI or ISO standard drill sizes. If you must have a non-standard bore, ask yourself: can an off-the-shelf bushing or insert solve this?

Replace Machined Features with Sheet Metal or Off-the-Shelf Parts

This is the single most powerful cost-reduction technique we use at PreciseMaker. A machined bracket with an L-shape costs 3–5× more than the same geometry made from bent sheet metal. Threaded holes? Use PEM inserts instead of machining threads into thick stock. Linear guides? MISUMI has a standard rail that does exactly what your custom-machined channel does.

Before: Solid aluminum block, CNC machined on 4 sides, 6 setups.

After: Bent 5052 sheet metal + 4 PEM inserts + 2 MISUMI rails. Same function, 60% cheaper.

Design for the Largest Possible Tool

Bigger tools remove material faster and deflect less. If your design forces the shop to use a Ø2mm end mill for a feature that could accept a Ø6mm tool with a small design tweak, you're paying for that choice in machine time.

Rule: Give every feature the largest possible internal radius your design can tolerate.

Minimize Setups

Every time the operator has to unclamp, flip, and re-indicate your part, you're paying for setup time. A part that requires 4 setups costs roughly twice as much as one that needs 2.

Fix: Design features so they can be accessed from the same side, or at most two opposing sides. Consider whether a 4-axis or 5-axis machine can reach everything from fewer setups.

Don't Specify a Surface Finish You Don't Need

Specifying Ra 0.8µm on a surface that's hidden inside an assembly is throwing money away. Each finish — as-machined, bead-blasted, anodized, polished — adds cost and lead time.

Rule: Only specify surface finish on visible, tactile, or functional surfaces. Let the rest be "as-machined."

The Bottom Line

DFM isn't about cutting corners. It's about knowing which corners don't matter. At PreciseMaker, we apply these principles from the first sketch — because we don't just design parts, we machine them too. And we know exactly what drives cost on the shop floor.

Need a DFM review of your design? Send us your files →

*Tags: CNC machining, design for manufacturing, DFM, cost reduction, precision manufacturing, SolidWorks, mechanical design*