Cross-hole drilling is difficult because the drill can lose support as it enters or exits the intersecting hole. This guide is for process engineers planning offset or intersecting holes and deciding whether a standard drill, flat-bottom drill, or staged process is safer. When one cutting edge is supported and the other is suddenly unsupported, the drill can deflect, chip, leave a burr, or break.
The intersection position changes the tool choice
If the cross hole only touches part of the drill path, a standard drill may still have enough guidance. If the intersection is centered and the drill point remains engaged, the process may also be manageable. The worst case is an offset intersection where the drill point loses guidance while one side of the tool is still cutting.
In that third case, any drill that depends heavily on a point for guidance can walk or bend. A flat-bottom drill or similar geometry may be reviewed because it can enter difficult surfaces without relying on a long center point in the same way.
Do not ignore entry and exit conditions
Cross holes are not only a tool problem. Workholding, bushing support, pilot condition, feed reduction near the intersection, and chip evacuation all matter. If the part wall is thin or curved, the drill may need a milled flat, a guide hole, or a staged process.
- Map where the intersecting hole meets the new hole path.
- Check whether the drill point remains supported at entry and breakthrough.
- Reduce feed where the tool loses support.
- Use a short, rigid setup and control runout.
- Expect burr control to become harder at the exit edge.
When a flat-bottom drill helps
A flat-bottom drill can be useful for angled, curved, or interrupted surfaces because it is less dependent on a conventional drill point. It is not a free pass to run aggressively. The process still needs stable entry, correct feed, and enough rigidity to keep the hole on position.
For related entry problems, see HEYI’s article on drilling angled surfaces with flat-bottom drills. For carbide drilling review, start from carbide tools and send the cross-hole drawing, intersection position, material, hole diameter, depth, tolerance, and current drill failure photos through the RFQ form.