What is knurling?

Short Answer:

Knurling is a machining process used to create a rough, patterned surface on a cylindrical workpiece. It is usually done on a lathe machine by pressing a hardened roller with a specific pattern against the rotating workpiece. The main purpose of knurling is to provide a better grip on tools or machine parts.

This process is commonly used on handles, knobs, and shafts where a non-slippery surface is required. Knurling not only improves appearance but also helps in fitting parts together by slightly increasing the diameter of the workpiece.

Detailed Explanation:

Knurling

Knurling is an important operation performed on a lathe machine to produce a decorative or functional pattern on the surface of a cylindrical workpiece. It is not a cutting process but a forming process, where a patterned hardened steel roller is pressed against the rotating surface of the workpiece. This roller displaces the surface material plastically, forming raised ridges or patterns. The resulting textured surface improves grip, enhances appearance, and may also help in creating interference fits between components.

Knurling is widely used in mechanical workshops and manufacturing industries for producing surfaces that need to be handled by hand, such as tool handles, instrument knobs, machine levers, and bolts. It is also used when a tight press fit between two components is required.

Purpose of Knurling

The main purposes of knurling are as follows:

  1. Improved Grip:
    The rough surface created by knurling helps prevent slipping when holding or operating a component, especially in tools and handles.
  2. Aesthetic Appearance:
    Knurling gives a professional and finished look to the component by adding a patterned surface design.
  3. Interference Fit:
    When a shaft is slightly undersized, knurling can increase its diameter slightly, allowing a tight press fit with another component.
  4. Identification:
    Knurling patterns can also be used to distinguish between different types of tools or machine controls.

Working Principle of Knurling

Knurling is performed on a lathe machine using a knurling tool that consists of one or more hardened steel rollers with specific tooth patterns. The workpiece is mounted on the lathe and rotated at a slow speed. The knurling tool is then pressed firmly against the rotating surface. Due to pressure, the pattern from the roller is imprinted on the surface of the workpiece.

Unlike cutting operations, knurling does not remove material. Instead, it displaces the metal to form a series of ridges and grooves corresponding to the pattern on the rollers. The operation requires steady feed and pressure to ensure uniform depth and clean pattern formation.

Types of Knurling Patterns

The pattern formed on the workpiece depends on the type of knurling wheels used. Common knurling patterns include:

  1. Straight Knurling:
    In this type, the lines are cut parallel to the axis of the workpiece. It is used when axial grip or decorative finish is needed.
  2. Diagonal Knurling:
    The lines are cut diagonally to the axis of the workpiece, forming a slanting pattern. It is mainly used for aesthetic purposes.
  3. Diamond Knurling:
    It is the most common type, where two sets of diagonal lines intersect to form a diamond-shaped pattern. This type offers the best grip and is widely used in tool handles and machine levers.

Knurling Tool and Setup

A typical knurling tool consists of one, two, or three knurling rollers. These rollers are mounted on a tool holder and have hardened patterned surfaces. The tool is fixed on the lathe tool post and positioned against the workpiece.

During operation, proper lubrication is necessary to prevent damage to the rollers and to ensure a clean finish. The speed of the lathe is kept low to allow the knurling rollers to properly form the pattern without slipping or tearing the surface.

The knurling tool should be aligned properly with the center of the workpiece to avoid uneven patterns or double tracking (where two overlapping patterns are formed).

Steps in Knurling Operation

  1. Mount the workpiece firmly in the chuck of the lathe.
  2. Select the appropriate knurling tool and install it on the tool post.
  3. Adjust the lathe to a low speed setting.
  4. Bring the knurling tool in contact with the rotating workpiece.
  5. Apply steady pressure until the pattern is clearly formed.
  6. Move the tool along the surface to cover the desired length.
  7. Use cutting fluid for better surface finish and longer tool life.

Applications of Knurling

Knurling is widely used in various fields such as:

  • Manufacturing of tool handles, wrenches, and grips.
  • Producing control knobs and instrument dials.
  • Enhancing grip in machine levers and fasteners.
  • Creating interference fits between mechanical components.
  • Improving surface appearance of decorative machine parts.

Advantages of Knurling

  • Provides better grip and handling comfort.
  • Enhances appearance of the product.
  • Can slightly increase diameter for tight fits.
  • Simple and quick to perform on a lathe.
  • Improves usability of hand tools and control parts.

Limitations of Knurling

  • Improper setup may cause double tracking or rough finish.
  • Excessive pressure may damage the workpiece or tool.
  • Not suitable for thin or delicate materials.
  • Requires low speed and proper lubrication for best results.
Conclusion:

Knurling is a useful lathe operation that forms a rough, patterned surface on cylindrical workpieces. It is mainly used to improve grip, appearance, and fit between parts. The process uses hardened rollers that press against the rotating workpiece to form raised ridges in various patterns such as straight, diagonal, or diamond. Knurling is simple but requires careful alignment and steady pressure for an accurate pattern. It plays an important role in toolmaking, machine parts manufacturing, and general workshop operations.