Lathe Tool Bits by Material and Area of Use

The types of lathe tool bits are as follows:

Types of Lathe Tool Bits by Material

Tool Steel Bits

These are bits containing 0.5-2% carbon. Their quality and cutting endurance are low. They can withstand temperatures up to 250°C. The normal hardness of tool steel bits is around 50-60 Rc. The hardness decreases in direct proportion to the increase in operating and friction temperature. Tool steel bits are generally preferred as solid (unbrazed insert) bits.

High-Speed Steel (HSS) Bits

These are bits made from alloyed premium steel containing metals such as 2.20% C, 14% W, 1% Mo, 2% V, 5% Co (H 14-1-2-5)… They’re called HSS (High Speed Steel). Speed steel bits have high durability. High-speed steel bits maintain a hardness of 60 Rc unaffected up to 600°C.

HSS bits are selected according to standard square cross-section sizes (8, 10, 12 mm).

Carbide-Tipped Bits

These bits are more suitable for mass production work. They have the ability to machine very hard materials and operate at high temperature. Because of this, they can operate at high cutting speeds. The tips are used either brazed onto the bit body or mounted with screws. The life of a tip increases in proportion to the number of cutting edges it has. Because the carbide tip is brittle, it doesn’t withstand impact. As can be seen from the relevant diagram, carbide-tipped bits maintain a hardness of 80-90 Rc up to 800-900°C.

When carbide tips are made, certain metal carbides in powder form are mixed with the binding agent cobalt and pressed into molds. They’re then hardened by firing at 1400-1600°C in special furnaces. An example composition ratio for a carbide tip’s material could be as follows:

Tungsten carbide (WC): 29-92%
Tantalum carbide (TaC): 2-65%
Cobalt (Co): 4-18%

Carbide tips are identified by markings according to their usage group: P (blue), M (yellow), K (red).

Many machine manufacturers on the market call this type of tip a “diamond tip.” However, as you’ll see in the section below, diamond tips are cutters with a quite different appearance and machining capacity.

Ceramic-Tipped Bits

These are hard, non-magnetic bits made of ceramic. Made in a way similar to carbide tips, ceramic tool tips are made of aluminum oxide (Al2O3) and TiC (titanium carbide), and are harder than carbide.

Ceramic bits have a hardness of 85-95 Rc and can operate at temperatures above 1500°C. When a ceramic tip goes dull, it cannot be resharpened — that means its life is over.

Diamond-Tipped Bits

These are the hardest bits, used for taking thin chips at very high cutting speeds, and used to machine very hard materials (special alloy steels, hard stones…). The hardness of diamond bits is 100 Rc.

Diamond tips are made either synthetically (monocrystalline, MCD) or by sintering diamond powder (polycrystalline, PCD). The sintering process happens by baking, in a special furnace, a 0.5-1.5 mm thick layer of diamond powder coated onto a carbide tip.

Lathe Tool Bits by Area of Use

• Roughing bits: Used for rough stock removal and similar turning operations.
• Finishing bits: Used for light chip removal and finishing operations. The tip of the bit can be ground flat (wide) and used for taking very thin chips (as a burnishing/finishing bit).
• Facing bits: Used for facing and shoulder turning (in some cases used like a roughing bit).
• Grooving bits: Used for grooving and similar turning operations.
• Parting-off bits: Used for cutting-off and part-splitting operations.
• Form (profile) bits: Used to machine surfaces to a specific profile (shape).
• Boring bits: Used for boring holes.
• Thread-cutting bits: Used for cutting screw threads.
• Special bits: Used to perform certain special turning tasks.

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