Mastering DFM: 5 Essential Tips to Lower Your CNC Machining Costs

Mastering DFM: 5 Essential Tips to Lower Your CNC Machining Costs

In the world of precision engineering, the difference between a successful project and a budget-breaking one often happens before the machine even starts running. At Accura CNC Supply, we see thousands of designs every year. The most efficient, high-quality parts all have one thing in common: they were designed with DFM (Design for Manufacturing) in mind.

If you are looking to shave costs off your next production run or speed up your prototyping phase, here are five essential DFM tips to optimize your parts for CNC machining.

1. Avoid Sharp Internal Corners

CNC milling tools—such as end mills—are cylindrical. This means they naturally leave a radius when cutting internal corners. Designing a part with perfectly sharp 90-degree internal corners requires specialized equipment or manual filing, which adds significant cost and time.

The Fix: Always design internal corners with a radius slightly larger than the radius of the cutting tool. If you use a 1/4" tool, a corner radius of 0.130" (slightly larger than 0.125") allows the tool to move through the corner without stopping or vibrating.

2. Limit Hole Depth-to-Diameter Ratios

Deep holes are a common requirement for manifolds and housings, but they come with risks. As a drill bit goes deeper, it becomes more prone to "walking" (wandering off-center) and breaking. Furthermore, clearing chips from deep holes is difficult, which can lead to poor surface finishes.

The Fix: For the best results and lowest cost, try to keep hole depths within 3 to 4 times the diameter. If you must go deeper, be prepared for increased labor costs associated with specialized "peck drilling" cycles and high-performance tooling.

3. Don’t Over-Tolerances Everything

It’s tempting to apply a "standard" tight tolerance (like +/- 0.001”) to every dimension on a drawing. However, unnecessary precision is a major cost driver. Tight tolerances require more frequent tool changes, slower feed rates, and more rigorous inspection steps.

The Fix: Only apply tight tolerances to critical mating surfaces or functional features. For non-critical dimensions, stick to standard tolerances (usually +/- 0.005” or higher). This allows our machines at Accura CNC Supply to run at peak efficiency, passing the savings on to you.

4. Design for Standard Tool Sizes

Custom tooling is expensive. If your design requires a unique slot width or a specific hole diameter that doesn’t align with standard fractional or metric tool sizes, a machine shop may have to order a custom ground tool just for your job.

The Fix: Consult a standard tool chart before finalizing your dimensions. Designing around standard sizes (1/8”, 1/4”, 6mm, 10mm) ensures that we can start your job immediately using our high-quality in-stock inventory.

5. Simplify Part Complexity

Every time a part needs to be flipped or rotated to machine a new face, a new "setup" is required. Setups involve manual labor, alignment checks, and potential for error.

The Fix: Try to design your parts so they can be machined in as few setups as possible (ideally one or two). If a part is incredibly complex, consider if it can be designed as two simpler parts that are bolted or welded together. While 5-axis machining (available at Accura CNC Supply) can handle complex geometries, reducing setups will always be the fastest way to lower the price per unit.

Partner with Accura CNC Supply for Your Next Project

At Accura CNC Supply, we don’t just cut metal; we provide solutions. Whether you are in the early stages of prototyping or ready for a full production run, our team is here to help you optimize your designs for the best possible results.

Ready to get started? Contact us today for a quote or upload your CAD files to see how our precision machining services can bring your vision to life efficiently and affordably. Email [email protected] — we respond within 24 hours.