How to Choose the Right Drill Type

Carbide drills used for deep-hole drilling, flat-bottom holes, and micro-diameter holes must offer high functionality and reliability. Each application, however, presents its own technical challenges. This article outlines those challenges and the carbide drill technologies used to address them.

Drills for
Deep-Hole Machining

Challenges in
Deep-Hole Drilling

Chip Evacuation Issues

Deep-hole drilling makes chip evacuation difficult.
When chips accumulate, they may be recut, leading to jamming, abnormal wear, sudden tool breakage, and poor hole straightness. Solutions include high-pressure internal coolant systems and edge geometries that break chips into smaller pieces for easier evacuation.

Heat Buildup and Tool Wear

In materials like stainless steel and titanium alloys, high cutting resistance and low thermal conductivity cause heat buildup at the cutting edge.
This leads to rapid wear, thermal expansion of the tool or workpiece, and loss of dimensional accuracy.
Efficient heat dissipation using high-pressure coolant directly at the cutting edge, as well as thermal-resistant coatings, can help maintain performance.

Maintaining Straightness

Maintaining hole straightness is difficult in deep-hole applications.
Variations in material density or chip blockage can cause tool deflection, causing the tool to deviate from its intended path.

When Deep-Hole Drilling
Is Required

Holes with depth-to-diameter ratios over 10×D typically require deep-hole drilling techniques.
Such holes are common in parts requiring internal flow paths or long shafts—e.g., fuel system bores in aircraft parts, engine cooling holes, hydraulic manifold blocks, valve spools, surgical instruments, and precision fluid control components.

Drills for
Flat-Bottom Holes

Challenges in
Flat-Bottom Drilling

Uneven Hole Bottoms

Drills rotate during cutting, and the center moves slower than the periphery.
This can result in poor chip evacuation and uneven cutting near the center, leading to a raised or rough center area (dogbone shape) as the tool wears.

Edge Chipping in Intersecting
or Corrective Holes

In intersecting hole applications or when modifying existing holes, the tool may intermittently hit the workpiece, causing impact loads.
This increases the risk of micro-chipping, especially with brittle carbide materials.

Frequent Tool Changes

Flat-bottom holes often require multiple tools for pre-drilling, finishing, and spot facing. Frequent tool changes increase machine downtime and setup errors, leading to inconsistency in precision and quality.

When Flat-Bottom Drilling
Is Required

Used for counterbores for bolt heads, smoothing intersecting hole junctions, or creating flat surfaces for mating and mounting.
A smooth, uniform surface is critical for proper part fit, sealing, and assembly alignment.

Drills for
Micro-Diameter Holes

Challenges in
Micro-Hole Drilling

High Breakage Risk
Due to Tool Fragility

As drill diameters shrink, rigidity decreases.
Even minor resistance changes or chip clogging can exceed the tool’s strength and cause instant breakage.
Solutions include using high-rigidity carbide materials and through-coolant designs for stable chip evacuation.

Difficult Chip Removal

Due to the small hole diameter, chip volume is relatively large. Chips tend to accumulate, placing excessive stress on fragile tools and increasing breakage risk.

Machine Accuracy
and Runout Sensitivity

Even slight machine runout or vibration can drastically affect results.
Spindle or toolholder vibrations can cause the drill tip to deviate from center, leading to oversized holes or poor roundness.
Dynamic runout must be minimized and controlled prior to machining.

When Micro-Hole Drilling
Is Required

This technology is essential in fields where hole precision directly impacts performance.
Examples include via holes in high-density PCBs, precision clock parts, microcatheters, medical fluid components, and injector or inkjet nozzles—where tolerances are measured in microns.