Turning Tools

Turning is a versatile machining process with multiple possibilities for shaping and forming a workpiece. The flexibility, performance, and quality of the cutting technology are assured by the machine type itself and the type of the tools. I accentuate the fact that the tool type has a significant impact on the surface quality. That is the reason why we will discuss this topic profoundly.

To understand the difference between turning tools, first, we should discuss the different types of turning operations for external and internal cutting.

Each operation from the list above is realized by a specific tool. Before we discuss more about the tools used in turning operations, let’s take a look at their design and components.

Turning Holder

The holder assures strong support for the insert minimizing the vibration during machining. For this reason, they are made from heavy, forged steel. These types of holders are dedicated to external operations. The turning holder body generally doesn’t have a sophisticated design as the insert, though there are quite a few choices. Holders can also channel the coolant efficiently to the cutting edge of the tool. They are grouped by form, angle, size, and marked with letters and numbers as the standard (ISO) requires.

Identification Code for Turning Holders:

Clamping method of insert

P C L N C 25 25 – M 12

Exists 5 different clamping methods, these vary depending on the insert type, shape of the tool and the level of rigidity during machining.

Insert Shape

P C L N C 25 25 – M 12

See on the insert nomenclature (beneath).

Holder style

P C L N C 25 25 – M 12

Clearance angle

P C L N C 25 25 – M 12

See on the insert nomenclature (beneath).

Hand of turning tool holder

P C L N C 25 25 – M 12

The orientation of the tool holder has three options: left, neutral, or right-handed. This aspect is useful in machining because it enables multiple options for cutting.

Height of Shank

P C L N C 25 25 – M 12

The 6^th part of the code, which in our example is 25, means that the height of the tool holder is equal to 25 mm.

Width of shank

P C L N C 25 25 – M 12

The 7^th part of the code, which in our example is 25, means that the height of the tool holder is equal to 25 mm.

Length of holder

P C L N C 25 25 – M 12

The length of the holder is given by a table, where each letter symbolizes a number.

Length of insert cutting edge

P C L N C 25 25 – M 12

See on the insert nomenclature (beneath).

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Inserts

Turning inserts are made in a variety of materials, composites, coating, and geometry to ensure high quality and fast material removal. Thanks to genius engineering, they are easy to be changed and some of them can be indexed to be used on other edges when one of them has deteriorated.

Insert materials are usually carbide but exist other types like ceramic, cermet, or diamond application too. A top coating protects the material for higher durability and more efficiency in cutting.

Type of Inserts Material:

• Cemented carbide: HW- uncoated, HC- coated
  • The most common material used in the industry. High resistance to abrasion.
• Cermets: HT -uncoated, HC-coated
  • Cemented material based on titanium carbide (TiC) or titanium nitrides (TiN) or both. Extremely high resistance to abrasion.
• Ceramics: CA- oxide ceramics, CM- mixed ceramics, CN- nitride ceramics, CC-nitride ceramics-coated
  • Ceramics are extremely resistant to heat and are used in high-speed applications but they are really fragile.
• Cubic Boron Nitrides: BN
  • A hard substance used in very hard machining, it has an extremely high resistance to abrasion and toughness. Involves running the tool or part fast enough to melt it before it touches the edge.
• Polycrystalline diamonds: DP- uncoated, HC-coated
  • The hardest substance. Superior resistance and unsuitable for steel machining.

Identification code for Inserts:

In the following, I will explain the meaning of each letter and number in the insert’s identification code and how you can decode it.

Insert Shape

C N M G – 12 04 08

Inserts come in a variety of shapes, sizes, and thicknesses. The impact of the insert shape in machining is the following: 

• round shape- maximizes edge strength; 
• diamond-shaped- cut fine + features;
• octagonal shape- uses separate edges when one edge after another is worn out;

What is the difference between large and small point angle insert? For example, the difference between machining with V= 35° and W=80° angle insert? Small point angle is often the preferred choice for finish machining, while large angles for rough machining for its strength. Rough machining means high feed, increased cutting forces, and vibration. The exact opposite is the surface finish machining, where the vibration and cutting forces decrease with weaker cutting edge, but more possibilities in the execution of details.

Clearance Angle

C N M G – 12 04 08

Clearance angle is essential because, during cutting, the insert’s wall rubs against the workpiece. The insert’s angle guarantees the minimum touching surface between the two elements. That is the reason why a 0° angle insert is used mostly in rough machining.   

Insert Tolerances

C N M G – 12 04 08

The insert tolerances mean tolerances in different insert sizes such as length, height, thickness, etc.

Turning Insert Types

C N M G – 12 04 08

This letter tells us about the insert hole shape and chip breaker type. The chip breaker is a feature on the insert’s surface, ensuring the chip breakage in short segments rather than long ones.

Look at the next pictures: LEFT side – insert WITHOUT chip breaker; RIGHT side – WITH chip breaker.

Turning Insert Size

C N M G – 12 04 08

This nomenclature symbolizes the cutting-edge length of the turning insert. A fact to notice is, the cut depth should never exceed ½ of the diameter of the inscribed circle of the insert.

Insert Thickness

C N M G – 12 04 08

The insert thickness is measured from the bottom of the insert to the top of the cutting edge.

Nose Radius

C N M G – 12 04 08

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Carbide Insert Seat

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Boring Bars

Drills

In CNC machining can be used a wide variety of drills like twist, insert, and others. Selecting the right drill depends on the material type being cut and its thickness and speed.

Spot Drills

Spot drills are high precision drills used before twist drilling, and their role is to cut an accurate hole for a secondary operation. The purpose of spot drilling is to make a little dimple “pre-hole” in the workpiece ensuring the right position for the following twist drilling.

Center drills

Center drills are used to create a 60 center at the end of the steel bar. They have a smaller section on both endings of the tool and are very rigid. Center drills come in different sizes, angles, materials, and coatings. The workpiece is fixed and centered through the hole on the lathe machine for following operations.       

Taps

Taps create inner threads with specific sizes and lengths defined in the standard (ISO). Tapping requires a premade hole, which has to be smaller than the thread size (see in the example below).

Single Point Thread Mill

A single point thread mill is a cutter whose shape is the thread form. The tool rotation is synchronized to the rotation of the part, describing the thread form. Passing the hole, the mill cuts deeper and deeper to form the thread.

What is the difference in machining using a single point thread mill or a tap?

A single tap is suitable for just one metric size (for ex. M6, M8, M12), while a single point thread mill applicable for multiple thread sizes on a workpiece. Using the mill saves us precious time by tool changing and machine setting.

Reamers

Its purpose is that enlarges an existing hole to precise tolerance and creates a high-quality surface. This operation requires an existing hole with accurate size and finish. It’s important to notice that the hole diameter must be close to the final diameter so that the reamer must remove just a bit of material.