Design & Technical Drawings

Why can’t CNC produce a perfectly sharp internal corner, and how should the correct inside radius be chosen?

A truly sharp internal corner is not realistic in CNC machining because the cutter has a diameter; the inside radius should be chosen around tool access, strength and function.

Why does this matter?

These details look small on a drawing, but they can change tooling, cycle time and even whether the feature is practical to machine. A few good design decisions early can avoid special tools and later revisions.

Why can’t CNC produce a perfectly sharp internal corner, and how should the correct inside radius be chosen?

What should you check?

  • critical geometry and interfaces
  • nominal dimensions, tolerances and datum relationships
  • fit, assembly and reference-surface expectations
  • a revision-controlled CAD and drawing package
  • available cutter diameter and tool access
  • mating-part contact geometry

A practical evaluation sequence

Start with what the feature actually needs to do. Before fixing a radius, hole or slot dimension, check how a tool can reach it, what cutter size is realistic and whether the depth ratio is sensible.

Common mistakes

  • Assuming every CAD feature is equally easy to machine
  • Treating tool access and chip evacuation as separate from part function
  • Leaving features that require special tooling to be discovered during quotation
Decision rule

Define the geometry around both function and a realistic machining route.

What should you send for evaluation?

  • available CAD, drawing or physical sample details
  • critical dimensions, tolerances or fit expectations
  • material and any finishing/heat-treatment requirement
  • target quantity, lead-time expectation and use case

Where can Gizmak help?

We review critical surfaces, dimensions and repeatability alongside the manufacturing method and inspection plan.

Precision machining

08 / Enquiry

Do you have a real part, drawing or CAD file?

Use the guide as a starting point, then share the actual technical data or physical sample so the manufacturing route can be reviewed against the real project.

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