HSK Tool holders and BT Tool holders are some of the best tool holders available. CNC’ers searching for high precision tools to enable them to craft their projects with high degree of precision and accuracy can utilise these tooling items to their benefits.
Although Tool holders and cutting tools play vital roles in any high-speed machining operations. Tool holders are of different types and brands. And there is certain difference observed in the various brands of tool holders.
Being developed in Germany, HSK tool holders are symmetrical tools designed to help manufacturers and end users boreholes, cut through a material piece, and perform other forms of high-speed machining operations with top-notch quality.
On the other hand, BT tool holders are also symmetrical with greater stability and balance during high-speed operations. These tooling systems are similar in various aspects, but there are slight changes that make the big difference.
Whether HSK tool holders or BT tool holders, tool holders are generally built with the same basic anatomy. And a better understanding of the key difference between HSK and BT holders can be seen in the anatomy of the tooling systems.
Anatomy of Tool holders
1. Retention Knobs:
The tool holder is kept in the spindle by a retention knob. When the wrong retention knob is used, the tool holder may fly out of the spindle during machining operations. This situation may be unsafe and dangerous to the machine operator. In some cases, retention knobs are designed in a hollow-like pattern, allowing coolants to flow through the tool holder. During operations, the clamping set (located in the spindle) holds the retention knob, pulling the tool holder up into the mouth of the spindle.
This is the part of the tool holder that is conically shaped. Normally, the taper has a tolerance level of 0.0002″ for both the outer diameter tolerance and the taper tolerance. Usually, the taper’s of the HSK tool holders are relatively shorter than that of the BT holders.
3. V-Flange: This is the part of a tool holder that gets locked into the automatic tool changer during machining operations – especially when the tool is moved in a to and fro pattern from the tool changer to the spindle.
4. Collet Pocket: This is the part of the tool holder where the collet is inserted and secured by collet nuts.
HSK and BT Tool Holders – The Major Differences
HSK Tool Holders are widely used across the United States. Despite its popularity and high market acceptance, this tool holder is widely misunderstood. And users fail to grasp the full potential and application of the HSK Tool holder.
Unlike the HSK tool holders where its full functionality is not fully understood, the BT Tool holders have high market acceptance, and they’re symmetrical about the spindle axis. This implies that BT tool holders have great balance and stability during high-speed machining operations.
Some of the basic difference between HSK and BT Tool Holders are:
1. Taper: One of the basic difference between HSK and BT Tool holders are the taper ratio. The HSK is designed with a 1:10 taper while the BT Tool holders use a 7:24 taper.
2. Dual Contact Point:
The dual contact nature of the HSK holder is really striking. In the HSK tool holder, the spindle contact with the taper and flange while BT holders are designed with the spindle in contact with the taper alone.
3. The positioning of the Drawbar: The drawbar fingers in an HSK Tool holder is located inside the shank while the drawbar fingers of the BT tool holders are wrapped about the exterior surface of the retention knob as it holds the tool holder inside the spindle.
Manifestation of the Major Differences Between HSK and BT Holders During High-Speed Machining HSK Tooling System is primarily designed to offer repeatability, accuracy, and fast tool changing. Although the BT holders are of great value, they show some limitations at a high spindle speed of 8,000 rpm.
The heavyweight of BT 40 or BT 50 tool holders offers some sense of security while an HSK adapter of the same dimension is relatively lighter. Notwithstanding, the lightness of the HSK tool holder is of great benefit during high rotational motion, making it outperform the BT holders during high-speed machining operations. During high-speed machining, radial and axial heat growth are experienced at the spindle shaft and taper.
In the BT holder, radial growth is experienced, making the tool holder to be pulled deeper into the taper. This leads to the loss of accuracy in the Z-axis. Due to the hefty mass of the BT tool holder, slow heat growth is also observed, causing a loss of the solid fit and radial stiffness of the taper. The gradual loss of the solid fit gives way to the development of chatter (or resonance).
When the hsk system is subjected to thermal effect, the hsk adapter cannot be pulled from its place by the retention system. This is due to the axial location of the hsk adapter and the flange-to-flange connection with the spindle nose. And also, the hsk taper shank and the spindle taper tends to heat and grow evenly.
Unlike the BT holders, the high-speed rotation has a positive impact on hsk holders as their grip is increased by an increase in rotational speed which leads to a corresponding increase of the centrifugal force.
Ultimately, better radial and axial stiffness are observed in the hsk tool holder, leading to high accuracy, repeatability, and top-notch surface finishing.
With hsk holder types A, B, C, D, E, and F, users also have an opportunity to choose their preferred hsk tool holder for a specific project.
Conclusion – HSK or BT Tool holders?
BT tool holders have served so well in the past. And they’ve been used for several low-speed cutting.
On the other hand, hsk holders are high-speed machining tools designed for the future as they’re of immense value for both low speed/high torque applications and high speed/low torque applications.
Although each tool holder is uniquely designed and has its up and downsides, the hsk tool holders is a better choice for manufacturers and end users looking for tool holders with greater precision and accuracy.