Discover 5 proven ways to reduce CNC machining costs before sending your CAD file. Learn how smart DFM choices save time and money with Ashland Engineering.
Every mechanical engineer wants to design the perfect component. However, perfection on the screen often translates to unnecessary expense on the shop floor. The harsh reality of subcontract manufacturing is that machine time and setup complexity dictate the final price.
Before your CAD model ever hits our CAM software at Ashland Engineering, your design choices have already determined the required tool changes, workholding strategies, and inspection hours. If you want to optimize your manufacturing budget without sacrificing component integrity, you must design for manufacturability (DFM).
Here are five ways to engineer out the unnecessary costs before you send your final CAD file.
1. Open Up Non-Critical Tolerances
Applying a blanket tight tolerance across your entire drawing is the fastest way to drive up your quote. While our ISO9001-certified CNC department can reliably hit strict tolerances, doing so requires slower feed rates, frequent tool changes to compensate for wear, and intensive digital metrology inspections.
How to fix this:
- Apply strict tolerances (e.g., ±0.01mm) strictly to critical mating surfaces, bearing fits, or sealing grooves.
- Allow standard, looser tolerances for clearance features, external aesthetics, and non-functional profiles.
- Remember that over-tolerancing directly increases cycle time and scrap risk—both of which you pay for.
2. Enlarge Internal Corner Radii
An end mill is a rotating cylinder. It is physically impossible to machine a perfectly sharp, 90-degree internal corner without resorting to secondary processes like wire EDM or broaching. If your CAD file has sharp internal corners, it immediately flags a custom tooling requirement.
Even small radii can be costly. If a 30mm deep pocket requires a 2mm corner radius, we have to use a tiny, fragile end mill that requires a massive reduction in Material Removal Rates (MRR) to prevent tool deflection or breakage.
How to fix this:
- Ensure all internal vertical corners have a radius larger than the tool required to machine the pocket depth (ideally a depth-to-diameter ratio under 3:1).
- Add a small floor radius instead of a sharp 90-degree intersection where the pocket floor meets the wall.
- Use “dog-bone” or undercut reliefs in corners if a mating square part absolutely must fit inside the pocket.
3. Standardize Hole and Thread Sizes
Machining custom or obscure thread pitches requires specialized taps or time-consuming thread milling interpolation. Similarly, specifying a hole diameter that does not align with standard drill bit sizes forces the machinist to plunge with an end mill and circular interpolate the hole, which is much slower.
How to fix this:
- Stick strictly to standard metric (M) or imperial UNC/UNF thread profiles.
- Ensure hole depths do not exceed 4x the drill diameter to prevent chip evacuation issues and tool breakage.
- Design all holes to be machined perfectly perpendicular to the surface. Drilling into an angled face requires custom fixturing or spot-milling to prevent the drill bit from walking.
4. Minimize Deep Pockets and Thin Walls
Material removal is efficient until the pocket gets too deep or the remaining wall gets too thin. Pockets with a depth greater than four times their width require extended-reach tooling. This drastically increases the risk of tool chatter and deflection, forcing us to slow our feeds and speeds to a crawl to maintain surface finish.
Similarly, extremely thin walls (under 1.5mm in aluminium, for example) are prone to vibration and warping from the heat generated during machining.
How to fix this:
- Decrease pocket depth wherever structural integrity allows.
- If a deep cavity is required, widen the pocket to allow for larger, more rigid tooling.
- Maintain a minimum wall thickness of 1.5mm to 2mm for standard metal components to allow for aggressive, cost-effective roughing passes.
5. Design for Minimal Machine Setups
Every time a component has to be manually removed from the CNC vice, flipped, aligned, and re-probed, you are paying for setup time. A part that requires machining on all six faces takes significantly longer to produce than a part where all features can be accessed from a single orientation.
How to fix this:
- Try to design all primary features (holes, slots, complex profiles) on a single face, or two faces maximum.
- If multiple angles are required, assess if a continuous multi-axis profile can be simplified into a standard 3-axis operation.
- Split highly complex components into two simpler parts that can be machined easily and bolted or welded together during assembly.
Partner with a Machining Expert
The most expensive manufacturing process is the one that requires guesswork and rework. By applying these DFM principles, you ensure your designs are optimized for efficient, reliable production.
At Ashland Engineering, we don’t just hit “cycle start” on flawed designs. Our engineering team reviews every drawing to ensure you are getting the most efficient, cost-effective CNC machining process possible.
Ready to get your optimized parts into production? Send your CAD files to Ashland Engineering today for a transparent, highly technical review.
