CNC design rules that cut cost + lead time.
These CNC machining design guidelines are the rules of thumb our engineers use when they review your drawing. Limits vary with material and part, and we confirm them for yours before the job goes out for sourcing.
Design breaks a rule?
Send it anyway. Some parts have to break rules, and the jobs other suppliers turn down are often the ones we’re built for. Our engineers review every drawing, flag what drives cost, and tell you what a change would add.
Quality + Compliance
AS9100D Compliant · ISO 9001:2015 · ISO 13485 Compliant · ITAR Registered · NIST 800-171 Compliant
Features + tolerances
Where most of the cost hides.
- Tolerance
- ±0.005" standard. Tighten only what controls fit + function.
- Surface finish
- Call out finer finishes only where a surface seals or slides.
- Inside corners
- Radius larger than the cutting tool.
- Corner radius
- Near 1/3 of pocket depth or more.
- Pockets
- No deeper than about 4x their width.
- Walls
- 0.030" minimum in metal. 0.060" minimum in plastic.
Holes + setups
Fewer tools, fewer setups, faster parts.
- Drill sizes
- Standard sizes wherever you can.
- Hole depth
- About 4x diameter. 10x at most.
- Threads
- Engagement about 1.5x diameter.
- Setups
- Put features on as few faces as possible.
- Multi-axis
- 4- or 5-axis where it saves setups.
- Edges
- Break 0.005" to 0.015". Chamfers beat fillets.
Why it matters
Every tighter callout adds machine time, inspection and scrap risk. A round cutter can’t make a sharp inside corner. Thin walls vibrate and warp as material comes off. Every extra setup adds fixturing, handling and a chance for misalignment.
CNC design questions
±0.005″ is standard for most machined features. Shops in our vetted network hold ±0.001″ where the part needs it, but every tighter callout adds machine time and inspection. Tighten only the features that control fit + function.
Keep pockets to about 4x their width, with inside corner radii near 1/3 of the pocket depth or more. Deeper pockets need longer tools, which deflect and chatter, so they cost more and hold tolerance less reliably.
Plan on 0.030″ for metal and 0.060″ for plastic. Thinner walls vibrate and warp as material comes off, which drives scrap and inspection time.
Send it anyway. Our engineers review every drawing, flag what drives cost, and tell you what a change would add before the job goes out for sourcing.
Keep going
More on how we source machined parts.
