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Deep-hole drilling isn't just a toolpath — and part of it isn't a G-code problem at all

CNC deep-hole drilling machines like those from IMSA and CHETO do something most machines don’t: drill cooling channels (“waterlines”) tens of times deeper than their diameter through the solid blocks of injection and die-casting molds — often on combined machines that switch automatically between a gundrilling spindle and a milling spindle, feed gun drills from a changer, and tilt the workpiece to drill angled channels. Programming them is genuinely different: you’re not just defining a toolpath, you’re controlling depth, chip evacuation, tool-breakage detection, special cycles, guide-bushing support, and process monitoring on a hole that can be metres long.

It’s worth being honest up front about a split that matters here. Some of that is process physics that no G-code verifier resolves — whether the chips actually evacuate, whether the coolant pressure is right, whether the hole drifts off straight over its depth, whether a worn bushing introduces vibration. Those stay in the domain of process engineering, tooling, and setup. But a large part of the risk is in the program and the machine’s motion — the cycles, the parameters as programmed, the drilling↔milling switchover, the angled-hole orientation, the changer sequence, the coaxial start geometry, and the collisions — and that part is exactly what you can prove before the machine runs.

The common programming pains

Depth and feed vs hole diameter. The depth-to-diameter ratio is critical; a setting too aggressive for the diameter breaks the tool or drills out of tolerance. The values are in the program — and their cutting load can be modelled.
Chip evacuation (peck, pressure, exit). If the cycle doesn’t manage peck, coolant pressure, and chip exit, the hole packs and quality collapses. The cycle structure is programmable; the actual evacuation is process physics.
Tool-breakage / process control functions. Machines like IMSA expose specific parameter- and tool-breakage-control functions; a program that doesn’t use them correctly raises the scrap risk.
Drilling↔milling synergy. On combined machines, the automatic switchover between the gundrilling and milling spindles/units creates sequence and offset errors if the program doesn’t handle the changeover correctly.
Workpiece orientation and clamping. For axial and off-axis (angled) holes, the block must be oriented and clamped precisely — and a small misalignment becomes a large error over the depth.
Post-processor and machine-specific cycles. These machines use dedicated cycles (often on Heidenhain or Siemens, with builder-specific functions), so a standard CAM program may not be enough.
Long holes in one cycle. At high depth the program must stay stable and account for the process controls the machine provides.

And, decisively: the guide bushing

Guide-bushing (and steady-rest) management is often decisive in deep-hole drilling — it governs centring, tool stability, and initial chip evacuation. In programming terms, the pains are: bushing–workpiece coaxiality (if the bushing isn’t on-axis, the hole starts crooked and the error grows with depth), bushing diameter choice (too tight or too loose changes tool support and hole quality), bushing wear/replacement (a worn bushing degrades guiding and introduces deviation), and compatibility with the part geometry (non-flat surfaces, diameter steps, repeated positions). The program has to assume a correctly sized, correctly positioned bushing coaxial with the tool — and if it doesn’t, the result is an off-centre start, ineffective peck, or an early tool break.

What's process physics vs what verification can check

Being clear about the boundary makes the tool useful rather than over-sold:

Process physics (not G-code verification): actual chip evacuation, coolant-pressure effectiveness, hole straightness/drift over depth, vibration, and bushing wear. These are tooling, coolant, and setup disciplines. Where verification touches them is cutting load — an accurate model of the program’s forces, torque, power, chip thickness, and material-removal rate flags a depth/feed too aggressive for the diameter (the tool-break risk) and helps keep the settings sane.
Program and motion (verifiable before the machine runs): the machine-specific drilling cycles and their parameters as programmed; the drilling↔milling switchover sequence and offsets; the workpiece orientation and angled-hole positioning; the gun-drill/cassette changer sequence; the coaxial start geometry between tool, bushing, and hole as modelled; travel and overtravel on a long stroke; and collisions or near-misses between the long gundrill, the steady rests/bushings, the workpiece, and the tilting table.

Why a listing and CAM simulation miss the program side

Machine-specific cycles and functions aren’t in a generic toolpath. The Heidenhain/Siemens deep-hole cycles, the builder’s gundrilling process-control functions, the automatic drill/mill switchover, the changer, and the tilting-table kinematics are behaviours of the real machine and control — not the toolpath the CAM drew. A standard CAM program may not even contain the dedicated cycles the machine needs.

A generic simulation doesn’t know this machine. The combined gundrill/mill spindles, the changer, the rotary/tilting table for angled waterlines, the steady-rest positions — a simulation not built on that configuration can’t tell you the switchover offset is wrong, the angled orientation misses, the changer sequence collides, or the drill starts off-coaxial with the bushing. It shows a plausible toolpath because, as a path, it is — the problem is in the machine’s cycles, sequence, and geometry.

Catching the program side needs the real ISO executed the way the installed control runs it, on a twin of the actual IMSA/CHETO — cycles, switchover, changer, table and all.

Where Eureka G-Code fits

Eureka G-Code builds a digital twin of your IMSA or CHETO deep-hole drilling/milling machine — the separate gundrilling and milling spindles, the automatic switchover, the gun-drill changer, the rotary/tilting table, the steady rests and bushings — and executes the real ISO the way the installed control (Heidenhain, Siemens) runs it, including the machine-specific cycles and functions. It’s the program-side verification, done properly:

The machine-specific drilling cycles run the way the control executes them, so a missing or mis-parametered cycle, or a standard CAM program that doesn’t handle the dedicated cycle, shows up as wrong or absent behaviour.
The drilling↔milling switchover runs on the twin, so a sequence or offset error at the changeover surfaces before it’s a wrong cut.
The angled-hole orientation (rotary/tilting table) is verified, so a misorientation shows as a hole in the wrong place or angle against the model — the error that grows over depth.
The gun-drill/cassette changer sequence is verified for collision and correct state, the way a head/tool change is.
The coaxial start geometry between the tool, the bushing/steady-rest, and the hole is checked as modelled, along with collision and near-miss among the long gundrill, the steady rests, the workpiece, and the table — and overtravel on the long stroke.
Cutting load via Eureka Chronos flags a depth/feed too aggressive for the diameter, the leading indicator of tool breakage.

And because mold drilling runs long, often unattended, the same verification supports lights-out safely (with Eureka Cloud queuing the checks) — on mold blocks worth a great deal, where a crash or a wrong waterline is expensive. What it doesn’t do is the process physics — chip evacuation, pressure, drift, vibration, bushing wear — which remain tooling and setup work; Eureka’s job is to make sure the program and the machine’s motion aren’t what goes wrong.

> Take a mold-drilling program with angled waterlines and a drill/mill switchover — the one that tilts the block, changes gun drills, and starts holes through a bushing — and run the real ISO on a twin of your IMSA/CHETO in Eureka G-Code. Watching the cycles, the switchover, the changer, and the coaxial starts resolve the way the control will, before the machine touches an expensive mold block, is how the program-side mistakes get caught at a desk.

FAQ

Can a simulator verify deep-hole drilling?

It can verify the program and the machine’s motion — the machine-specific cycles and parameters as programmed, the drilling↔milling switchover, angled-hole orientation, the changer sequence, coaxial start geometry, collisions, overtravel, and (via cutting-load analysis) whether the depth/feed is too aggressive for the diameter. It cannot verify the process physics — actual chip evacuation, coolant-pressure effectiveness, hole drift, vibration, or bushing wear — which remain tooling and setup disciplines.

How does the guide bushing enter into programming?

The program has to assume a correctly sized bushing positioned coaxially with the tool. If it doesn’t — wrong diameter assumption, an off-axis start, or geometry incompatible with the part surface — the hole starts crooked, the peck is ineffective, or the drill breaks early. A twin checks the coaxial start geometry and the collisions; the physical bushing condition and support remain setup.

Why isn't a standard CAM program enough for an IMSA or CHETO?

Because these machines use dedicated deep-hole cycles and builder-specific process-control functions, often on Heidenhain or Siemens, plus an automatic drill/mill switchover and a changer. A generic CAM program may not contain or correctly handle those, so the real behaviour only appears when the actual program runs on the real control — which Eureka G-Code does on a twin.

Does it check the drilling-to-milling switchover and the changer?

Yes. It executes the switchover and the gun-drill/cassette changer on the twin the way the control does, so a sequence or offset error at the changeover, or a changer collision, shows up before the machine runs.

Does it help with tool-breakage risk?

Indirectly and usefully: Eureka Chronos models the cutting load — forces, torque, power, chip thickness, material removal — so a depth/feed too aggressive for the diameter, the leading cause of gun-drill breakage, is flagged. The breakage-detection function on the machine is separate; verification helps you not provoke it.

Next step

Eureka G-Code — request a demonstration on a digital twin of your own machine and controller.

Prove the program and the motion on a twin of your deep-hole machine — cycles, switchover, changer, angled starts and collisions — and leave the chips, pressure and drift to the process, not to chance.