CNC Burr Control: Through Holes, Intersecting Bores and Tool-Exit Edges

A burr is displaced or projecting material left at an edge after cutting. On a cover plate it may mainly affect handling, but at a dowel bore, seal, guide slot, thread, oil passage or clean cavity it can obstruct assembly, scratch a mating part, cut a seal, retain chips or create contamination. A blanket note such as “no burrs” therefore gives too little information for process planning and acceptance. The RFQ should identify functional edges, the required edge condition, areas where loose material is prohibited and the expected inspection method. This separates a safe-handling requirement from a controlled geometric edge.

Classify edges by function instead of imposing one note on the entire part. One edge may be accessible but next to a datum; another may be deep inside an intersecting bore. The table is a DFM discussion aid, not a default acceptance standard.

The most stable approach is often to reduce burr creation before adding a cleaning step. Tool wear, runout, weak support, recutting chips and an unsupported exit layer all worsen the edge. Depending on geometry, the process engineer may consider drilling from both sides, adding backing support, moving the exit to an accessible area, or using a dedicated chamfering operation. An angled exit or a bore crossing another bore changes the engagement continuously, so the strategy must be tested with the actual material and setup. There is no universal feed, chamfer or edge radius for every part.

Options include on-machine chamfering, back-deburring tools, manual scrapers or stones, brushing, mass finishing and specialized processes. Each has limits. Manual work is flexible but depends on access and consistent work instructions. Mass finishing can blend many edges yet may affect finish, corner definition or small dimensions and does not guarantee a clean deep bore intersection. A cross-hole tool needs the main- and cross-bore diameters, depth, intersection angle, eccentricity and material. Chemical, thermal or electrochemical routes should only be considered when the requirement, material and qualified supply chain have been confirmed; they are not default VietTech operations.

If an edge needs defined geometry, specify the chamfer or radius with an appropriate tolerance rather than relying on “break edge.” For edges of undefined shape, ISO 13715:2017 provides a method for indicating the permitted edge condition and deviation; it does not replace normal dimensioning for a defined edge such as 1 × 45°. Separate loose-burr restrictions, safe-handling edges and assembly-critical edges. Applying one generic value to small bores, threads, seals and outer edges can create conflict. Ambiguous symbols or notes require an RFI before quotation or manufacture.

Burr inspection is not one universal measurement. Suitable lighting or magnification can reveal projecting material and secondary burrs; a borescope may help at internal intersections, subject to access. A thread gauge verifies thread function but does not prove every burr has been removed. A dimensioned chamfer or radius needs a matching geometric method. For high-risk edges, define sampling, observation area, acceptance limit and any process validation. Chip removal and cleanliness are separate requirements: a deburred part is not automatically proven clean to a specified cleanliness level.

Provide a controlled 2D drawing and matching 3D model; identify cross-holes, seal edges, dowel fits, fluid paths and no-scratch surfaces. State whether the edge is dimensioned or only needs sharp-edge removal, how loose burrs are treated, any cleaning requirement and a mandatory inspection method. Include material, heat/surface condition, prototype and production quantities, and report needs. VietTech performs CNC machining, edge treatment and inspection within the scope confirmed for each drawing; specialized deburring or treatment is evaluated separately and may be coordinated with qualified partners.

• Mark functional and inaccessible edges
• Dimension chamfers/radii when geometry matters
• Separate burr, cleanliness and appearance requirements
• Agree on inspection method and sampling

This article uses ISO 13715:2017 for undefined-edge indication, NIST research on burr formation and removal, and application guidance from HEULE and Sandvik Coromant for intersecting or angled-exit holes. These sources explain principles only. Final edge dimensions, tools, cutting data and acceptance criteria must follow the drawing, contract standard and validation on the actual part.