Knurling; What? Why? How?
What is Knurling?
Knurling is a process that can add a rough, patterned surface to a material.
Mostly preformed on round or cylindrical parts, the pattern is created by cutting or forming the material into the specified pattern. Knurling patterns are a combination of vertical, horizontal or angled lines. The most common patterns include: straight, annular, square (a combination of straight and annular) or diamond.
Knurling can be used in many applications. It is widely used on tools and equipment that are handled under sub-optimal grip conditions such as wet or oily hands.
Straight knurling can facilitate a coupling connection with very high torque resilience while allowing components to be made with much lower tolerances compared to typical press fit precision.
A mixture of diamond and straight knurling is often used on metallic parts that are to be over-moulded with plastic or composite details to add mechanical bonding to an otherwise limited chemical bond.
Advantages and Disadvantages of Knurling
Advantages
- Provides a gripping surface on machine and instrument handles
- Provides an adhesive/traction surface when used in over-moulding polymer or composites to a metallic component
- Can be used as a lower cost/precision alternative in press fit connections
- Can hide the appearance of wear
Disadvantages
- Knurling deforms the material surface which can result in reduction of overall strength and fatigue life.
- Unsuitable for hard and brittle materials
- Variations in process, tool wear and material properties can make the outcome inconsistent
Knurling Process
There are two types of knurling process, machine knurling or hand knurling. The choice between the two depends on the desired texture, material and pattern.
Machine Knurling
Most knurling is preformed using a lather for cylindrical parts or a milling machine for flat surfaces. The workpiece is clamped and the knurling tools are pressed onto the surface. This method generate a lot of heat, therefore lubrication is essential in order to avoid galling or cold welding (sticking) between to the knurling tool.
Hand Knurling
A more traditional processes, but similar in method, hand tools are pressed into the workpiece in order to deform the material. Hand knurling is more suitable for small application such as jewellery making.
