Cutter Bit / Tool Holder

Generally, the term tool bit or cutting bit refers to non-rotating cutting devices used in metal lathes, shapers and other machining equipment. For single-point cutting instruments, this kind of method is often generally referred to as the name of the specified sentence. The cutting edge is ground to suit a specific machining operation, and can be reground or reshaped as needed. When cutting, the ground cutter bit is rigidly fixed by the cutter holder. The tool holder is a device that safely provides a critical interface between the cutting tool and the CNC machine tool spindle. The cutting tool is installed in the tool holder and tightened, so it will not move or vibrate during processing. Provide the stability you need to ensure accurate cutting every time with your cutter bit.

Mounting Styles of Tool Holders and Cutter Bits

When choosing the tool holder for your cutter bit, you need to specify the installation style. R8 is used by most conventional machine tools produced after 1965; however, this taper is rarely used in today's high-speed machining equipment. There are four common sizes of morse taper tool holders (MT): #1, #2, #3 and #4. Each size has a taper fit and can be replaced quickly.

The National Machine Tool Manufacturer of the United States defines the NMTB taper for all CNC milling machines. The standard is 3.5 inches per inch, and a tie rod may be required. To standardize the tools of its devices, Caterpillar developed the CAT mounting type tool holders. Names including CAT-40, CAT-50 and CAT-60 refer to NMTB tapers. BT is similar to CAT, but equilibrated and symmetrical along the rotation axis. BT uses the same symbol for calculation of the NMTB main body taper, but uses metric pull stud lines. The Hollow Tool Holder (HSK) is designed to improve cutter bit grip as the speed of the spindle increases.

It has no pull studs and is used with HSM as a norm. VDI is designed specifically for fast tool shift. Two variations of the dovetail and the straight shank are available. Tool holders are also issued that use base mounting tools (BMT) and straight shank tools.

CAT and BT tool holders

The size range of CAT tools is CAT 30, CAT 40, CAT 50, etc. This number refers to the taper of the tool or cutter bit of the Manufacturing Technology Association. The CAT tool holder was developed for Caterpillar Tractor Company and is sometimes referred to as a V flange tool.

They are sturdy in design and are mainly used in a range of applications from precision machining to heavy roughing. This type of tool holder is supported by ATC technology. With the help of the fixed knob, the tool holder body is pulled into the milling spindle and centered by the tapered contact. The spindle speed of the steep taper tool is up to 12,000 rpm. CAT and BT tool holders have the same NMTB body taper and look very similar, which is why they are often confused. However, the CAT tool holder uses inch threads as a fixed knob, while the BT tool holder uses metric threads. Visually, you will notice the difference in flanges. The flange of the CAT tool holder is thinner than the flange of the BT tool holder. 

HSK tool holders

The HSK tool holder is a relatively new design, very common on European machine tools imported into the United States. HSK is an abbreviation of ‘Hohlschaftkegel’ which is German for hollow taper shank. They do not have the fixed knob of the CAT tool holder, but have a hollow handle. The clamping mechanism in the HSK tool holder operates from the inside and contains a segmented collet that expands radially under pressure. The chamfer of the collet matches the inner wall of the shank so that it can be locked firmly when the pull rod is actuated. 

In the HSK tool, the clamping force generated on the flange is twice that of the CAT type tools and cutter bits. The resulting increased clamping force is due to the simultaneous connection of taper and flange spindle. The radial stiffness produced in this way is five times that of the tapered tool holder. The HSK tool holder is balanced for high-speed machining of the tool head. Compared with the CAT tool, the tolerance between the spindle receiver and the taper is smaller. HSK tool holder has some advantages over CAT tool holder, especially in high-speed milling machine spindle, tool collision and maintenance. 

The HSK tool post is lighter, so the machine can accelerate and decelerate faster than the CAT tool post. When the spindle speed is higher than 8,000 rpm, the expansion speed of the spindle receiver is faster than the tool holder and the cutter bit. Due to the hollow design of the HSK tool holder, its tool holder is like a fuse, which will break in the event of a collision, thereby protecting the tool holder of the machine tool.

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