Most custom machining and prototyping projects cost far more than necessary - not because of high factory prices, but due to non‑optimized part designs. Many engineers prioritize perfect functionality on CAD files but overlook manufacturability, resulting in extra tool changes, repeated setups, tight unnecessary tolerances, and secondary operations that significantly raise production costs.
The good news is: you do not need to change your part's core function to cut costs. With simple design optimization and basic DFM (Design for Manufacturability) adjustments, you can reduce custom part costs by 20%–40% while keeping full performance, quality, and precision. In this article, XC Precision shares practical, factory‑verified design tips for CNC machining, sheet metal, plastic parts, and low‑volume production.
1. Relax Non‑Critical Tolerances (The Biggest Cost Saver)
Tight tolerances are the No.1 reason for inflated custom part quotes. Many designers apply ultra‑strict tolerances such as ±0.01 mm to every surface and hole "just for safety", even though most features do not require high precision for assembly or operation.
Cost logic: Tighter tolerances require slower machining speeds, multiple finishing passes, strict quality inspection, and higher scrap rates. Loosening non‑functional tolerances drastically reduces machining time and inspection workload.
Simple optimization rules:
Reserve ±0.01–±0.02 mm tolerance only for mating, fitting, and moving surfaces
Keep general non‑critical features at ±0.05 mm or ±0.1 mm (industry standard)
For clearance holes and non‑assembly planes, allow ±0.2 mm tolerance
This single adjustment often lowers the total cost by 15%–25% without any functional loss.
2. Standardize Radii, Holes and Hardware Sizes
Custom, non‑standard geometric features force manufacturers to use special tools, custom grinding, or repeated tool switching, which adds extra labor and machine time.
Common wasteful designs:
Non‑standard fillets like R2.3 mm, R1.7 mm instead of standard R2 / R2.5 / R3
Unique hole diameters that do not match standard drill bits
Custom thread sizes and groove widths
Optimization tip: Use industry‑standard radii, hole sizes, and fastener dimensions wherever possible. Standardized features allow factories to run faster with fewer tool changes, greatly improving production efficiency and reducing unit prices.
3. Avoid Excessively Deep Pockets & High Depth‑to‑Width Ratios
Deep, narrow cavities are one of the most difficult and costly features in CNC machining. Long, thin cutting tools easily vibrate and deflect, requiring slower cutting speeds, multiple passes, and higher risk of tool breakage.
DFM factory rule: Keep the pocket depth less than 4 times the tool diameter. If your design exceeds this ratio, manufacturers have to use specialized long tools or split machining processes, which increases both time and cost.
If deep cavities are unavoidable, you can optimize by:
Increasing inner corner radii
Slightly widening the groove width
Removing redundant material in non‑stress areas
4. Eliminate Unnecessary Undercuts & Secondary Operations
Every undercut, side groove, hidden slot, or tiny protruding feature requires extra machine setups or secondary EDM processing. Each additional setup means re-clamping, re-aligning, and manual inspection, which directly increases labor costs and lead time.
Before finalizing your CAD file, check:
Can any undercut be replaced with through‑hole or open‑side structure?
Can tiny decorative or non‑functional features be removed?
Can multiple small features be simplified into one unified structure?
Simplifying part geometry is the most efficient way to reduce hidden manufacturing costs.
5. Combine Multiple Small Parts Into One Integrated Component
Many designers split a single functional unit into several small parts for easier CAD modeling, but this leads to higher overall costs: more raw material consumption, more machining procedures, extra fasteners, and additional assembly labor.
Optimization strategy:
Combine simple adjacent parts into one integrated piece if assembly tolerance allows. Fewer parts mean fewer fixtures, fewer production runs, and fewer quality checks - significantly lowering overall project cost while improving structural stability.
6. Match Material Grade to Actual Usage Scenarios
Over-specifying materials is another common cost killer. Many projects use high-end materials such as Aluminum 7075, Stainless 316, or PEEK for ordinary structural parts that only require basic support.
Practical material cost optimization:
General structural aluminum: Use 6061 instead of 7075
Ordinary anti-rust parts: Use 304 stainless instead of 316
Common plastic housings: Replace high-cost PEEK/PC with ABS, POM, or TPE where applicable
Always select materials based on actual stress, temperature, and environmental requirements, not subjective high-standard preferences.
7. Optimize Wall Thickness for Plastic & Metal Parts
Uneven or over-designed wall thickness increases material waste, machining time, and molding risks. For CNC metal parts, overly thick walls mean more material removal; for plastic prototype and injection parts, oversized walls cause sinking, bubbles, and longer cooling cycles.
Recommended wall thickness:
Metal CNC parts: 1.0–3.0 mm (avoid ultra-thin fragile walls)
General plastic parts: 1.5–2.5 mm with uniform thickness
Uniform wall design ensures stable production, lower scrap rates, and reduced material costs.
Final Conclusion: Cost Reduction Starts From Design
Factory processing fees are relatively fixed - design determines 80% of your final custom part cost. By relaxing unnecessary tolerances, standardizing geometric features, simplifying complex structures, optimizing material selection, and reducing secondary operations, you can achieve obvious cost savings without sacrificing product quality and performance.
At XC Precision, our DFM team provides free design review and optimization suggestions for all CNC machining, sheet metal, 3D printing, vacuum casting, and injection molding projects. We help global clients balance high precision, stable quality, and competitive unit prices for prototyping and low-to-medium volume production.
Get Free DFM & Cost Optimization Support
Send us your CAD files (STEP/IGS) and project requirements today. Our engineers will analyze your design, list all cost-saving optimization points, and provide an accurate quotation within 24 hours.