Most of what makes a machined part expensive is decided in CAD, long before a single chip is cut. The good news: a handful of design adjustments can cut machining cost dramatically without changing how your part functions. Here are the ten mistakes we see most often — and how to design around them.
1. Deep Pockets
Deep, narrow pockets force long, thin tools that chatter, deflect, and cut slowly. As a rule, keep pocket depth under about 4× the tool diameter. If you need a deep pocket, widen it so a larger, stiffer tool can reach the bottom.
2. Sharp Internal Corners
A cutting tool is round, so it physically cannot machine a perfectly sharp internal corner. Specifying one forces tiny tooling and slow passes. Add a corner radius — ideally a bit larger than the tool radius — anywhere the design allows.
3. Unnecessary Tight Tolerances
Every tolerance you tighten adds cost in machining time and inspection. A blanket ±0.001″ across a whole part can multiply the price. Tolerance only the features that actually need it, and leave everything else at a standard tolerance like ISO 2768-m.
4. Thin Walls
Thin walls vibrate under cutting forces, which causes chatter and poor finish, and they can warp after machining. For metals, keep walls above roughly 0.030″; for plastics, go thicker. If a thin wall is unavoidable, expect added cost for careful, light passes.
5. Tall, Thin Features
Tall standing ribs and bosses deflect away from the tool and are fragile to machine. Keep height-to-width ratios reasonable (under about 4:1) or add fillets at the base for support.
6. Weird or Non-Standard Threads
Custom threads need custom tooling. Standard threads cut with standard taps are far cheaper. Stick to common metric or imperial sizes, and for small or soft-material threads consider threaded inserts instead of cutting threads directly.
7. Material Selection Mistakes
Picking a hard or gummy material when an easy-machining one would work adds real cost. Aluminum 6061 machines fast and cheap; stainless and titanium are far slower. Unless the application demands the harder material, design around the easy machiner — and tell your shop what actually matters about the material so they can suggest alternatives.
8. Features on Multiple Faces
Every time a part has to be flipped and re-fixtured to reach a new face, setup time (and cost) climbs. Consolidate features onto as few faces as possible. A part machinable in one or two setups is dramatically cheaper than one needing five.
9. Engraved Text and Fine Detail
Deep engraved text and fine cosmetic detail eat machining time with tiny tools. If you need markings, consider laser engraving as a secondary operation instead of machining them in — it’s faster and cleaner.
10. Designing Without Talking to Your Shop
The single most expensive mistake is finalizing a design without a manufacturability conversation. A five-minute DFM review can catch every issue above before it’s locked in. The best parts are designed with the shop, not thrown over the wall to it.
Design It Right the First Time
Send us your CAD early and we’ll run a free DFM review — flagging the cost drivers and suggesting changes that keep your part’s function intact while cutting the price. It’s the cheapest engineering you’ll ever get.
