Understanding Shrinkage in Heat Shrink Tool Holders: How It Works and Why It Matters

In modern CNC machining, heat shrink tool holders—also known as Shrink Fit holders—are widely used for their exceptional rigidity, balance, and precision. They are essential in high-speed and high-precision operations such as aerospace, automotive, and mold manufacturing. One common question from machinists and engineers is:
What is the shrinkage of a heat shrink tool holder?

Let’s dive into the concept and how it impacts performance in CNC machining.

Understanding Heat Shrink Tool Holders

A heat shrink tool holder (or shrink fit holder) is a high-precision CNC holder that clamps the cutting tool through thermal expansion and contraction. The holder bore is manufactured slightly smaller than the tool shank diameter. When heated, the bore expands, allowing the tool to be inserted. As the holder cools, it contracts tightly around the tool, creating a powerful and precise clamping force.

What Does “Shrinkage” Mean in Heat Shrink Tool Holders?

The term “shrinkage” in this context refers to the thermal contraction of the tool holder bore after heating. When the holder cools down, it shrinks back to its original size, tightly gripping the tool. The shrinkage amount is extremely small but crucial for:

• Runout Accuracy: Typically ≤0.003mm for Shrink Fit Tool Holders

• Holding Power: Ensuring the tool does not slip during high-speed cutting

• Balance and Stability: Essential for high-speed spindles like BT40 shrink fit holders and HSK shrink fit holders

How Much Shrinkage Occurs?

In practice, the bore expands by about 0.01mm to 0.015mm during heating, enough to insert the tool shank. Once cooled, the bore shrinks back to its nominal diameter, creating a uniform clamping force along the entire shank.

This controlled shrinkage provides several key benefits:

• High Concentricity: Improves tool life and surface finish

• Superior Balance: Ideal for high-speed CNC milling and drilling

• No Moving Parts: Unlike collet systems, shrink fit holders rely on material elasticity rather than mechanical components

Types of Heat Shrink Tool Holders

KURATA offers a complete range of shrink fit tool holders for various CNC machines:

• BT40 Shrink Fit Holders – Common in machining centers for automotive and mold industries

• HSK Shrink Fit Holders – Perfect for high-speed, high-precision spindles

• Shrink-Fit Extensions – For deep cavity milling in molds and aerospace parts

Why Choose Shrink Fit Tool Holders for CNC Machining?

• Micron-Level Accuracy: Tool body accuracy ≤0.002mm, runout ≤0.003mm

• High Clamping Force: Secure grip for heavy and high-speed cuts

• Thermal Stability: Consistent performance under varying temperatures

• Smooth Profile: Perfect for automated tool changers in modern CNC machines

The shrinkage of a heat shrink tool holder is a controlled thermal contraction that ensures exceptional tool clamping and precision. This technology makes shrink fit holders the ultimate choice for industries demanding high-speed, high-accuracy CNC machining. Whether you are using BT40 shrink fit holders, HSK Holders, or shrink-fit extensions, this method guarantees superior machining performance and extended tool life.