Solid Carbide Drills for Cross-Hole Intersections: How to Control Interrupted Cutting

Drilling into a cross hole can change a stable cycle into an interrupted-cutting event within a fraction of a second. As the drill reaches the intersecting passage, one part of the point may lose support while another continues cutting. Chips can change shape, coolant flow can be redirected, and the drill may leave a witness mark, burr or size variation at the intersection. The problem is not solved by selecting a drill from diameter alone.

Solid carbide drills for cross-hole intersections need to be planned around the complete feature, material and machine conditions. The entry surface, primary-hole depth, cross-hole size and location, drill geometry, projection, coolant route and inspection requirement all affect the result. A reliable process comes from identifying the interruption before the first part and proving the operation with a controlled sequence.

Read the intersecting feature before selecting the drill

Review the drawing for both holes, not only the hole currently being programmed. Confirm the diameter, depth, angle and positional relationship of the primary and cross holes. Note whether the drill will enter an existing passage, break into it near the bottom, exit through it or cross it at an oblique angle. Each configuration changes how much of the cutting edge is supported and where chips can move during the cycle.

Material condition also matters. Steel, stainless steel, cast iron, aluminum and other materials form chips differently, while stainless steel can work harden if the drill rubs or loses its cutting action. Include the actual material grade, heat-treatment condition and any surface treatment in the process review. A test in a short solid block does not necessarily predict what happens when the point meets an open cross passage in production.

Why an intersection increases edge load

The point does not see a continuous cut

In solid material, the point and margins have a relatively consistent support condition. At a cross-hole intersection, the drill may encounter a sudden void, then re-enter material. That transition can momentarily alter cutting force and chip formation. If the tool is already running with excessive projection, runout or an unstable holder, the interruption can become the point where one cutting edge chips or the drill begins to deflect.

For this reason, avoid treating the intersection as an ordinary depth coordinate. The drill must be matched to the material and intended depth range, and the cycle should begin with verified application data for the selected tool. The machine, holder, fixture and coolant system should be capable of maintaining stable conditions throughout the approach, intersection and exit.

Chip control changes when the passage opens

A cross hole can provide a new escape route, but it can also trap or redirect chips. The result depends on hole orientation, chip form and coolant delivery. Chips that collect at the far side of the intersection may be drawn back into the primary hole and recut. Inspect the chips during first-off approval and look for scoring, packed fragments, unusual noise or a sudden change in thrust load. These are useful early signs that the process needs adjustment.

Build rigidity into the drilling assembly

Use the shortest practical gauge length and a holder that clamps the shank securely. Clean the shank, collet or hydraulic bore and all contacting surfaces before assembly. Where hole tolerance or drill diameter warrants it, check runout close to the cutting end. Excess runout can load one margin more heavily and make an already difficult interrupted cut less predictable.

Workholding is equally important. Support the workpiece near the feature and confirm that clamping does not allow movement as the drill reaches the intersection. If the part has thin walls or a cavity around the intersecting holes, consider how the local section reacts to drilling force. Improving support or reducing projection is often a more durable correction than immediately changing cutting data.

Choose coolant delivery and cycle strategy deliberately

Internal coolant can be helpful when it reaches the point and carries chips from the hole, especially as depth increases. External coolant may be suitable for accessible, shallower conditions, but it must still reach the active cutting zone. Match the drill’s coolant design to the actual machine capability; coolant channels cannot compensate for contaminated fluid, inadequate pressure or a delivery route that never reaches the intersection.

Program the cycle with the intersection in mind. Avoid an unnecessary dwell or a sudden feed change that leaves the drill rubbing at the transition. Any feed adjustment, pecking method or programmed pause should follow the selected drill’s application guidance and be proven on representative material. Overuse of pecking can add repeated entries and exits, while no chip-management plan can create a packing problem in a deeper feature. Use a controlled trial to establish the appropriate method rather than copying a generic cycle.

Inspect the intersection, not just the finished diameter

A hole can measure on size at the entrance while still having a burr, interrupted surface or damaged edge at the cross-hole interface. Inspect the primary-hole diameter, depth, straightness as required, and the condition of both passages at the intersection. If the part function involves fluid flow, sealing, fasteners or a later machining step, include the relevant internal finish and burr criteria in the first-off review.

When an issue appears, trace it in sequence. Check the drawing relationship and operation order, then fixture support, projection, runout, tool condition, coolant path and chip evidence. Change one variable at a time and document the result. This approach prevents a program offset from masking a drill or setup problem that will recur at the next batch.

Practical checklist for cross-hole drilling

• Map the primary and cross holes, their relationship, material condition and required internal quality.
• Identify exactly where the drill enters, crosses or exits the existing passage.
• Select a solid-carbide drill by material, depth range and verified coolant arrangement.
• Use a clean, low-runout holder and the shortest practical projection.
• Support the part near the feature and prove the cycle on representative material.
• Inspect chips, burrs and the internal intersection condition as well as diameter and depth.

SDF drilling options and application support

SDF offers solid carbide drilling tools including reinforced 5×D internal-coolant drills, internal-coolant drills for stainless steel and internal-coolant drills for cast iron. For related process principles, see our guide to drilling on inclined surfaces.

If a standard drill cannot meet the required access, step geometry, depth, coolant route or intersection condition, SDF can review the drawing and machining details through the custom carbide tooling page or contact page.

FAQ

Why does a drill chip at a cross-hole intersection?

The cutting edge can lose and regain material support at the intersection. Runout, excess projection, poor chip evacuation, weak workholding or unsuitable cutting conditions can make that transition more severe.

Is internal coolant always required for a cross hole?

Not always. The suitable method depends on material, depth, accessibility, chip form and machine capability. The important point is that coolant reaches the cutting zone and supports chip removal.

Should the program slow down at the intersection?

Use a cycle strategy supported by the selected drill’s application guidance and prove it on representative material. An arbitrary slow-down can cause rubbing or chip problems.

What information helps select a drill for intersecting holes?

Provide the drawing, material, hole diameters and depths, intersection location, machine, holder, coolant method and the current quality or tool-life issue.