How to Fix Poor Chip Evacuation During Deep Hole Drilling

If you’ve ever battled tool breakage, oversized holes, or sudden chatter during deep hole drilling, chances are the real culprit isn’t your cutting edge—it’s poor chip evacuation. In CNC machining and production drilling, chip control is often the make-or-break factor for hole quality, tool life, and overall productivity.

In this article, we’ll explore:

• Why poor chip evacuation happens in deep holes,

• What problems it causes,

• And most importantly, how to fix it using practical solutions, tool design adjustments, and cutting strategies that actually work on the shop floor.

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Why Chip Evacuation Becomes a Problem in Deep Hole Drilling

Chip evacuation becomes increasingly difficult when the depth-to-diameter (D/D) ratio exceeds 3:1, and especially problematic beyond 5:1. In such situations, chips are trapped inside the flutes or bore, leading to:

• Built-up heat

• Tool jamming

• Poor surface finish

• Drill deviation or breakage

The longer the hole, the further chips need to travel, which increases friction and backpressure—especially in low-ductility materials like stainless steel, titanium, or certain hardened steels.

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Common Symptoms of Poor Chip Evacuation

• Burn marks around the hole edge

• Irregular hole diameter or taper

• Broken drill tips

• Excessive spindle load or alarms

• Chips being “pushed” instead of curled and cleared

• Shortened tool life and frequent downtime

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Solutions to Fix Poor Chip Evacuation

1. Use Coolant-Through Drill Bits

Coolant-through carbide drills are one of the most effective solutions for deep holes. They deliver high-pressure coolant (usually 10–70 bar or higher) directly to the cutting zone, which:

• Flushes chips out of the flutes

• Reduces heat buildup

• Increases feed rates while maintaining accuracy

Note: For holes deeper than 5xD, high-pressure coolant is a must.

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2. Apply Peck Drilling (Z-axis Intermittent Cutting)

In peck drilling, the drill bit retracts slightly after every small plunge to allow chip clearing. This is especially useful on machines without coolant-through capabilities.

Suggested Pecking Strategies:

Hole Depth	Peck Style
≤ 3xD	Full depth possible, no pecking needed
3–5xD	Moderate pecking (e.g., every 1–1.5xD)
≥ 5xD	Use small incremental pecks (e.g., 0.5xD)

Be cautious not to retract too quickly or too often, as this can increase cycle time and wear.

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3. Switch to Chipbreaker or Parabolic Flute Geometry

Tool geometry makes a huge difference. For deep drilling:

• Parabolic flutes are optimized for chip flow.

• Chipbreaker geometry helps split long, stringy chips into smaller, more manageable segments.

These drills also offer larger flute volumes, allowing chips to evacuate faster.

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4. Adjust Feed and Speed

Overfeeding or underfeeding can both create chip evacuation issues.

• Too fast = large chips that clog

• Too slow = chips rub and pack into the flutes

Use the manufacturer's recommended feed per revolution (f/rev) and surface speed, especially for deep drilling.

Example: For a 10mm solid carbide drill in steel at 5xD:

• SFM: 200

• Feed: 0.1 mm/rev

• Coolant: ≥20 bar recommended

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5. Use a Pilot Hole or Step Drilling Method

For extremely deep holes, starting with a shorter pilot drill or performing the operation in two or more steps can stabilize chip flow. This prevents chips from jamming at the entry point and gives coolant a better access path.

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6. Ensure Proper Chip Flushing with External Coolant

If you're working with a drill that doesn’t support internal coolant, make sure:

• Coolant nozzles are properly aligned with the drill flutes

• Flood coolant is consistent and hits the hole center

• Chip conveyors or air blasts are available to keep the work area clean

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7. Use Coated Carbide Drills Designed for Chip Evacuation

Choose drills with high-performance coatings like:

• AlTiN or TiAlN: For heat resistance

• DLC (Diamond-Like Carbon): For non-ferrous materials

• ZrN or TiCN: For sticky materials like aluminum or brass

These reduce friction and help chips slide out of the flutes smoothly.

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Final Thoughts

Poor chip evacuation isn’t just a nuisance—it’s a real risk to hole quality, tool life, and even machine safety. Fortunately, with the right drill design, coolant setup, and machining strategy, deep hole drilling can be efficient, accurate, and reliable.

If you’re producing holes 5xD or deeper regularly, upgrading to coolant-through solid carbide drills with chipbreaker geometry is one of the smartest moves you can make. Want help choosing the right drill for your material and depth? We offer custom solutions tailored for high-efficiency, deep-hole CNC drilling.