DESIGN FOR MANUFACTURING / CNC MACHINING INSIGHTS
Internal corners and pockets look simple in CAD, but they are frequent sources of RFQ questions. A milling cutter is round, so a pocket corner naturally carries a radius. Clear drawing notes help a buyer distinguish a cosmetic preference from a functional interface—and let the machining review focus on the features that actually matter.
Why milled internal corners have a radius
In CNC milling, the cutter removes material as it rotates. Its circular form leaves a radius where two internal walls meet. A CAD model can display a visually sharp inside corner, but that does not by itself explain how the corner should be produced or whether the corner is functionally critical.
Start by identifying the mating condition. If another part must sit into the pocket, an ordinary corner radius may interfere with its outside corner. If the pocket only provides clearance, a standard radiused corner may be entirely suitable. The drawing should make that distinction explicit rather than leaving it to a visual assumption.
Match corner intent to the assembly
| Design situation | Useful drawing information |
|---|---|
| Clearance pocket | State the required pocket envelope and any surfaces that locate a mating part. |
| Part seats into a pocket | Show the mating geometry and identify whether corner clearance or a relief feature is required. |
| Corner is cosmetic only | Do not assign an unnecessarily restrictive requirement; a stated radius preference is often clearer. |
| Functional internal corner | Identify the feature, its purpose and the permitted geometry on the controlled drawing. |
A small corner-relief feature may be appropriate when a square outside corner must meet an internal corner. Its geometry should be defined in the drawing or model rather than described only as “make it sharp.” That preserves the actual assembly intent for review.
Pocket depth is not the only question
For a deep pocket, the review needs the depth, width, length and corner radii together. Tool reach and access depend on that complete shape. A narrow, deep pocket can require a longer-reach tool; that changes how the feature is approached and may affect the review of wall condition, floor access and inspection approach.
Also show what is allowed at the pocket bottom. Is a flat floor important? Does a component contact the floor, or is there clearance below it? Are there through-features, threads or cross-holes entering the pocket? These details prevent the pocket from being treated as isolated geometry.
Give the review team a tool-access picture
Good RFQ information explains where a cutter can enter and where it cannot. Include sectional views for enclosed pockets, show any obstructions above the opening, and call out surfaces that must remain free of tool marks or contact. If a feature is accessible only from one direction, make that direction visible in the model or drawing.
The same principle applies to toleranced pocket walls and floors. A tolerance has the most value when it is linked to function. Our CNC tolerance guide explains why requirements should be specified around the features that affect fit, alignment or performance.
Use notes that answer the manufacturing question
Ambiguous notes create delay because they force a reviewer to infer design intent. Instead of “sharp corners,” identify the interface and the geometry required. Instead of “deep pocket,” give the controlled depth and the relevant opening dimensions. Instead of relying on a screenshot, provide the current model and PDF drawing in the released RFQ package.
For broader drawing preparation, see our guide to CNC drawing details that prevent delays. It covers the complementary information—material, finish, threads, critical dimensions and inspection notes—that belongs alongside pocket geometry.
Keep a sharp-corner request specific
A request for a sharp internal corner should never be treated as shorthand for an unspecified process. Explain why the corner must be sharp, show the mating geometry and identify what dimensions govern the interface. That lets the manufacturing review discuss a practical geometry without assuming capabilities or changing the design intent.
Make the pocket easy to review
ExactMach coordinates drawing-defined CNC milling, CNC turning, prototypes and custom parts around Shenzhen and Dongguan for international orders. When a pocket or internal corner affects fit, include the relevant drawing views and mating information so the requirement can be reviewed with the rest of the RFQ package.