Why We Avoid Tiny Slots in CNC Machining – A Manufacturer's Honest Explanation

Why We Avoid Tiny Slots in CNC Machining – A Manufacturer's Honest Explanation

In the world of CNC machining, it's common to receive part drawings with various detailed structures. Among them, one particular feature often triggers resistance from machine shops: tiny slots.

To many clients, a small slot may seem like a simple cut, but for machinists, it often represents high risk, low efficiency, and questionable feasibility. Today, we'll explain why we often avoid machining tiny slots—and what better alternatives we recommend.

What Are Tiny Slots?

A “tiny slot” typically refers to narrow, deep, hard-to-access grooves in a part. For example, a groove that's only 1mm wide but 10mm deep, or a blind slot tucked away in a sharp internal corner. While these may appear minor on a drawing, they are notoriously difficult to machine.

Why We Recommend Against Tiny Slots

1. Tooling Limitations

CNC tools—such as end mills and drills—have limitations in diameter and length. Ultra-thin tools under 1mm exist, but they are fragile, have short lifespans, and are expensive. If a slot has a depth-to-width ratio over 10:1, it approaches the physical limit of the tool, making breakage likely.

2. Poor Machining Stability

Tiny tools are prone to vibration or deflection, especially when cutting hard materials like stainless steel or titanium. The result is often rough walls and dimensional inaccuracy.

3. Chip Evacuation Issues

In narrow, deep slots, it's hard to flush chips out, and coolant can't reach the bottom. This often leads to tool jamming or burning.

4. High Cost, Low Efficiency

Tiny slots demand slower speeds, special tooling, and frequent cleanup, all of which drastically reduce efficiency. If machining fails, rework is costly—and the shop bears the risk.

What Are the Solutions?

Fortunately, there are better alternatives:

• Reconsider the Design: Can the same function be achieved using wider, shallower grooves or segmenting the slot?

• Use EDM Instead: For inaccessible slots, consider EDM (electrical discharge machining). It's slower and costlier but more reliable.

• Talk to Your Supplier Early: Engage your machining vendor during the design phase to align expectations and capabilities early on.

Conclusion

When we say “no” to tiny slots, it's not about being uncooperative. It's about managing risk and ensuring reliable production. We'd much rather help you optimize your design early, saving time and cost down the line.

In CNC machining, design for manufacturability is critical. Next time you're adding a slot to a drawing, ask yourself: Is this slot really necessary—and is it manufacturable?