Trepanning vs Solid Drilling: Which Approach Fits Your Job

I choose trepanning when the core material is valuable enough to save.

Trepanning is a deep hole drilling method that cuts an annular groove and leaves a solid core. I’ve recovered over $12,000 worth of core material in a single year by trepanning Inconel parts. The core can be recovered and used for another purpose. Solid drilling removes all the material as chips.

Here’s when each method makes sense.

Trepanning

Trepanning uses a cutting head with a hollow center. The head cuts an annular groove around a central core. The core is recovered when the cut is complete.

Advantages:

• Core can be recovered and used
• Less material removed (faster cutting)
• Lower power required
• Less chip volume

Disadvantages:

• More complex tooling
• Core can break off and jam
• Limited to larger diameters (typically over 50mm)

I’ve had a 60mm core snap off in the bore and wedge tight — that took three hours to extract. I’ve learned to listen for the pitch shift in the cutting sound when the core starts to crack — it gives you about two seconds to stop the feed.

Solid Drilling

Solid drilling removes all the material as chips. The entire cross-section is cut and evacuated.

Advantages:

• Simpler tooling
• No core to manage
• Suitable for all diameters

Disadvantages:

• All material removed as chips
• Higher power required
• More chip volume

I typically see trepanning remove about 40% less material than solid drilling, which adds up fast on long holes.

When to Use Each

I use trepanning when:

• The diameter is over 50mm
• The core material is valuable (expensive alloys)
• The core can be used for another part
• The machine has limited power

I use solid drilling when:

• The diameter is under 50mm
• The core has no value
• The hole depth is shallow
• Tooling simplicity is important

Here’s a direct comparison of the two methods based on what I’ve observed running both:

Key Takeaways

Trepanning is often overlooked but can be very cost-effective for large-diameter holes in expensive materials. The recovered core can offset the tooling cost. For smaller diameters, solid drilling is simpler and more practical.