Shenzhen Alu Rapid Prototype Precision Co., Ltd.
Industry News
Short answer: Most CNC cost is created at the design stage, not the machine. Following ten DFM (Design for Manufacturing) rules — especially loosening non-critical tolerances, increasing internal radii, and reducing the number of setups — typically cuts part cost by 20–40% with no loss of function.
Here are the rules we apply when we review a customer drawing, in order of impact.
1. Loosen Non-Critical Tolerances
Apply tight tolerance only to the features that mate. A part where every dimension is ±0.02 mm can cost 2–3× the same part at ±0.1 mm for the same function.
2. Increase Internal Corner Radii
Cutting tools are round. A sharp internal corner forces a small tool, which must run slowly and breaks easily. Make the radius as large as the design allows — ideally at least one-third of the pocket depth — and cost falls immediately.
3. Avoid Deep Pockets and Cavities
Depth-to-width ratios beyond about 4:1 require long, flexible tools, so feeds must drop. If you can split a deep cavity into two shallower parts that bolt together, do it.
4. Design for Fewer Setups
Every time a part is flipped or re-fixtured, the shop adds labor, alignment time, and error risk. Keep as many features as possible reachable from one direction. A part machined from four sides costs far more than one machined from two.
5. Use Standard Hole Sizes and Depths
Standard drill and reamer sizes reduce tool changes and cycle time. A non-standard hole diameter may require a special cutter that adds cost and lead time.
6. Keep Wall Thickness Reasonable
For aluminum, walls under about 0.8–1 mm tend to deflect and chatter, leading to scrap. For plastics, thin walls are even more problematic. Design walls thick enough to stay rigid during cutting.
7. Avoid Unnecessary Features
Every pocket, slot, thread, and chamfer adds cycle time. Ask of each feature: does it serve a function? Decorative micro-features are often the most expensive element on an otherwise simple part.
8. Standardize Threads and Avoid Unusual Ones
Use standard metric or inch threads. Odd thread pitches and deep tapped holes add tool changes and risk breakage. Thread milling or tapping to a reasonable depth is faster than chasing a thread to the bottom of a blind hole.
9. Choose a Readily Available Material
6061 aluminum and POM are the workhorses: cheap, stocked everywhere, and easy to machine. Moving to titanium or a specialty alloy can multiply both material and machining cost. Choose the cheapest alloy that meets the requirement.
10. Specify Surface Finish Only Where Needed
As-machined finish is free; anodizing, polishing, and powder coating are not. Restrict tight Ra callouts and cosmetic finishes to functional or visible surfaces.
The Cost Impact of Each Rule
| Rule | Typical saving |
|---|---|
| Loosen non-critical tolerances | 15–30% |
| Increase internal radii | 5–20% |
| Reduce number of setups | 10–25% |
| Replace premium material | 10–40% |
| Stop over-specifying finish | 5–25% |
These compound. Applying three or four of them routinely turns a borderline project into a viable one.
FAQ
What is DFM in CNC machining?
Design for Manufacturing — reviewing a design so it can be produced at lower cost and with fewer defects, usually by relaxing unnecessary requirements.
Do suppliers charge for DFM feedback?
A reputable supplier provides it free with the quote. It is in their interest as much as yours.
Does DFM feedback mean changing my design?
Not necessarily. Often it means confirming which tolerances and finishes you can relax, without changing the part's function.
How much can DFM realistically save?
20–40% is common on first-pass designs, especially for prototypes with over-specified tolerances.
When should I ask for DFM review?
Before the first production order, and ideally before finalizing the drawing.
Send Us Your Drawing
We will review it and tell you which three features cost the most — and exactly what to change. The quote and the feedback are free.