Free Printable CNC DFM Checklist
Twelve design-for-manufacturing rules to tick off before you send a drawing to a shop. None change what the part does — they keep it cheap, fast and in tolerance. Save the PDF and keep it by the CAD station.
1. Wall thickness ≥ 0.8 mm (metal), ≥ 1.5 mm (plastic)
Thinner walls chatter and deflect under the tool. If the design truly needs it, expect more setups and note it on the drawing.
2. Every internal corner has a radius
Sharp internal corners need EDM or tiny fragile tools. A standard corner radius (R0.5+) machines cleanly and cheaper.
3. Hole depth ≤ 4× diameter
Deep holes wander and snap drills. Open the back, or relax the position tolerance. State both if you can live with either.
4. Threads are standard sizes
M3/M4/M5/M6/M8 etc. Off-size taps are custom, slow and expensive. Use a standard size unless there's a real reason not to.
5. Tolerances only on critical dimensions
Every tight dimension costs time and inspection. Leave the rest at the standard commercial tolerance — mark what actually matters.
6. No overly thin fins or fragile features
They vibrate, break tools and scrap easily. Widen or support them, or accept a higher scrap rate and say so.
7. Hole diameters standardized
Fewer tool changes means faster, cheaper runs. Reuse a small drill set across the part where you can.
8. Vertical walls are fine (no draft needed)
Unlike molding, machining has no pull-out. Keep vertical walls if the function wants them — don't add draft by reflex.
9. Surface finish called out only where it seals or shows
Finish on every face wastes cost. Specify Ra only where it functions (a seal face, a sliding fit) — not across the whole part.
10. Designed for as few setups as possible
Re-clamping shifts dimensions. For multi-face parts, 5-axis holds features in one setup — call out the datum chain clearly.
11. Material grade chosen from function
Over-specifying material costs money for no gain. 6061 before 7075 unless the load truly needs it.
12. 3D model + 2D drawing sent together
One file alone invites guesswork. STEP/IGES + a PDF with GD&T gives the shop everything in one go.
Tick all twelve and the quote will come back lower and right the first time. If a rule can't be met, note it on the drawing so the shop plans for it instead of discovering it mid-run.
Want a second opinion on your drawing?
Send the STEP and PDF. We'll flag anything that adds cost without adding function — before you pay for the first part.
Related: Full CNC Design Guide · GD&T for Buyers · Tolerance Chart