Radii vs Sharp Corners: How Small Design Changes Impact Machining Costs
Radii vs Sharp Corners: How Small Design Changes Impact Machining Costs
In precision machining, a seemingly minor detail—an internal corner being sharp or rounded—can significantly impact the complexity, time, and cost of manufacturing. Many designers focus on structure and function early on, but often overlook a crucial factor: manufacturability. Let's explore how something as small as a corner radius can dramatically affect machining cost.
1. Sharp Corners Aren't So Simple in Machining
On a CAD drawing, sharp internal corners may look clean and logical. However, sharp 90-degree internal corners are extremely difficult to achieve directly through CNC machining. Standard cutting tools are cylindrical, meaning they naturally leave a radius in internal corners.
To achieve a true sharp corner, shops must use EDM (Electrical Discharge Machining) or extremely small diameter tools with multiple passes, both of which increase time and cost.
2. Rounded Corners Are More Machining-Friendly
In contrast, well-designed internal radii significantly improve machinability. Radii reduce tool stress at corners, enhance tool life, minimize chatter, and produce better surface finishes. It's generally recommended to design internal radii at least 1.5 times the tool radius.
For example: if the internal cavity is machined with a Ø10mm tool, designing a corner with R6 is ideal—it matches the cutter's radius and avoids extra operations.
3. Where Does the Cost Difference Come From?
We once had a customer submit a design with multiple sharp grooves on an aluminum part. It looked fine on the drawing, but machining required a tool smaller than 3mm to reach the corners, increasing cycle time by 45%. After adjusting the design to include R2 radii, we saved roughly 30% of machining time per part.
Key cost factors include:
• Complex toolpaths → longer programming time
• Small tools → slower feed rates & faster wear
• EDM or special operations → outsourcing or multi-step processes
4. Design Early, Save Big Later
For engineers, early communication with your machining partner saves rework and unexpected costs. Our advice:
1. Use radii in non-critical internal corners whenever possible
2. Base radius size on standard tool diameters
3. If a sharp corner is functionally necessary, specify tolerance and explain why
5. Conclusion
In CNC machining, small details can make a big difference. Choosing a radius over a sharp edge might seem trivial on a drawing, but in real production it can mean huge time and cost savings. Smart design often starts with a simple R.