Cross holes

Specify the intersecting passages, axis relationship and required opening. First breakthrough can occur before the full cross-hole opens into the bore.

In the ideal example, a 6 mm radial port enters a concentric tube of 15 mm outer and 10 mm inner radius. The center meets the inner wall at 5.000 mm depth. At the lateral edge it meets the wall at 5.461 mm. This is the intersection geometry before accounting for drill-point shape, far-wall clearance or tolerances.

Toolmakers treat these intersections as distinct machining features. Sandvik Coromant lists cross-holes for its CoroDrill DE10, while its detailed advanced-operation guidance says these operations are not recommended and supplies conditional starting guidance. HEULE distinguishes deburring solutions for uneven intersections, near-equal-diameter bores and main bores with several intersecting passages. These are named tooling applications, not proof that any drill or deburring tool suits every cross-hole. Sandvik DE10, HEULE X-BORES

Describe both holes and their relationship

Keep main-bore and cross-bore identities explicit. A useful drawing or manufacturing task identifies:

Define the intersection relative to datums rather than locating each hole from unrelated faces without reviewing the resulting tolerance stack. Two holes can meet nominally yet leave a reduced opening at accepted positional extremes. If the design needs a minimum opening or a complete cross-bore perimeter exposed inside the main bore, state that requirement separately from the two nominal diameters.

An angled or offset intersection is a three-dimensional edge, not generally a flat circular edge that can be represented by an ordinary entrance chamfer. Confirm the actual profile and tool-access envelope. HEULE specifically identifies crossing bores with center-axis offset as COFA-X application situations requiring tool selection. HEULE COFA-X application description

Original radial-port geometry example

Assume an ideal concentric tube with outer radius 15 mm and inner radius 10 mm. A 6 mm diameter radial cross-hole points exactly toward the tube axis and is perpendicular to the main bore axis. Measure depth inward along the cross-hole axis from the outermost entry surface. Ignore drill-point shape, burrs, tolerances and elastic effects.

The center of the cross-hole reaches the near inner wall after 15 − 10 = 5.000 mm. At the cross-hole's lateral perimeter, 3 mm away from its axis, that same cylindrical inner wall is farther from the entry datum:

depth = 15 − √(10² − 3²) = 5.461 mm.

Thus the theoretical near-wall intersection spans about 0.461 mm of axial depth across the port. Reaching the first central breakthrough at 5.000 mm does not establish that the full 6 mm port is open into the bore. This is a geometric illustration, not a programmed drill-tip depth or machining allowance. Actual tool-point geometry and its position must be added to a manufacturing plan, and the far wall must also be checked for unintended contact.

For a finished component, evaluate the accepted worst-case geometry. The example establishes neither a safe remaining wall nor a flow coefficient, pressure rating or stress-concentration factor. Fluid and structural qualification need the actual geometry and service conditions.

Plan the interrupted cut

Drilling into an existing passage changes engagement as the cutting edges leave material and may re-enter it. Review drill geometry, support, chip evacuation and the order in which the passages are produced. A cutting program for uninterrupted solid drilling should not automatically be reused across the intersection.

Sandvik's DE10 demonstration describes reducing feed through cross-hole and other advanced passages, while stating that drill length, stability and workpiece material influence the recommendation. This is guidance for that tool concept; it is not a universal feed-reduction percentage or permission to use the same strategy with another drill. The current product page specifies a minimum recommended diameter of the hole being crossed of 2× the cutting diameter. Keep that DE10-specific precondition separate from the original radial-port example. Establish cutting data from the selected tool's current application guidance and qualify the result. Sandvik DE10 demonstration and explanation

The sequence must also preserve the finished bore. Consider which operation creates the internal burr, whether a later finishing operation can reach it, and whether the tool can retract without damaging a functional surface. Do not assume that drilling the second hole completes all internal-edge processing.

Deburring is a separate operation

An accessible entrance edge can be inspected directly; an internal intersection may require different tools and evidence. HEULE's X-BORES page identifies COFA for sloped or uneven bore intersections, COFA-X for identical or nearly identical cross-bore diameters, and SNAP-X for main bores with multiple intersecting cross-bores. These descriptions organize application selection; they do not supply a universal edge radius, bore-ratio limit or acceptance guarantee. HEULE X-BORES scope, COFA uneven-edge applications

Brush Research Manufacturing describes Flex-Hone as another cross-hole deburring approach: the compliant abrasive tool reaches into the intersection and can create a radiused transition while improving the main-bore surface. Its April 2025 guidance requires lubricant and directs users to tool-selection/application instructions. That process changes surfaces as well as removing burrs; verify that the resulting edge and bore finish satisfy the part drawing. BRM cross-hole deburring guidance

Specify measurable acceptance rather than only “deburr.” Depending on function, resolve the maximum remaining projection, allowed material removal, edge radius or chamfer, and whether the bore must remain free of loose debris. Qualification on representative intersections should include the least accessible edge, not just the visible entrance. A toolmaker's successful application does not establish that the delivered part meets a different edge specification.

Inspection, cleaning and release

Plan access for inspection and cleaning before releasing the design. Distinguish proof that passages communicate from proof of their diameter, location, complete intersection, edge condition and cleanliness. A flow check or a probe passing through an opening answers only the requirement it actually tests.

Identify the inspection method and coverage appropriate to the internal geometry, for example a qualified visual/borescope examination or another agreed method where direct access is impossible. Define how chips, burr fragments and process residues are removed and how cleanliness is accepted. Do not equate burr removal with removal of every loose particle.

Maintain the drawing revision, datums, machining sequence, deburring method and final inspection record together. Any pressure, fatigue, sealing or moving-part requirement needs its own design and qualification basis; a visually clean cross-hole is not a component rating.

Source versions and related reference

Reviewed 2026-11-01, America/Los_Angeles. BRM's cited page prints 23 April 2025. The cited HEULE and Sandvik live product pages provide no independently verified technical revision date; the DE10 video is used for its stated application explanation without assigning a technical edition. No PDF upload or search timestamp is treated as a document revision. The radial-port example is original geometry under explicit assumptions.

Part features · Blind holes