Knurling wheels, also known as knurling dies, are used to create textured patterns or gripping surfaces on cylindrical blanks. They are commonly applied to materials like steel, brass, aluminum alloys, and hard plastics. Instead of cutting, the V-shaped teeth on knurling wheels deform and displace the material. The resulting embossed patterns, which are typically diagonal, diamond, or straight, often act as hand grips on handles, knobs, and rollers, though they can also be decorative. Knurling wheels are also available as sets.
Basics of Knurling Wheels
Learn common knurl types, patterns, and holders, and make sure your workpiece has the grip and finish it needs.
DIAGRAM OF A KNURL WHEEL
Knurling Wheels Basic Tips:
• Ensure the knurling tool's axis is parallel to the blank’s axis to prevent misalignment.
• Avoid overrolling—aim for about 90% pattern fill to prevent distortion.
• Use a higher feed rate on the first revolution. A deeper, wider initial impression helps the teeth track properly into the initial grooves for all subsequent revolutions.
Form and Cut Type:
Cut-type knurl wheels create textured patterns by cutting and removing material from the workpiece. This process reduces the workpiece diameter and is ideal for medium to larger-sized workpiece diameters. Form knurl wheels create patterns by displacing material, forming an impression without cutting. This increases the workpiece diameter and is ideal for small to medium-sized workpiece diameters.
Standard Knurl Wheel
Standard, also known as straight, knurl wheels have sharp corners on the leading edge. They are used where heavy loading is required.
Beveled Knurl Wheel
Beveled knurl wheels have a blunt leading edge to spread out loading. It requires higher forces on the tool and holder to displace material.
Convex Knurl Wheel
Convex knurls feature a sharp leading edge that helps distribute the load evenly during forming. They provide a smooth and precise finish.
Knurling Patterns:
Knurling Tip: Avoid traversing when using diamond knurls. For longer patterns, use a combination of left- and right-hand diagonal wheels.
Left-Hand Diagonal Knurling Wheels
Used in knurling to produce right-hand diagonal patterns. When paired with left- and right-hand wheels in a two-wheel knurling tool, they create a diamond knurling pattern. Commonly feature a 30° left-hand helix angle.
Right-Hand Diagonal Knurling Wheels
Produce left-hand diagonal patterns in knurling applications. When used with left- and right-hand diagonal wheels, they generate a diamond knurl. These wheels typically have a 30° right-hand helix angle.
Female Diamond Knurling Wheels
Designed to create a raised male diamond knurling. Female diamond wheels are only recommended if a two-wheel knurling tool is unavailable. The knurled blank should be close to the collet and large enough in diameter to prevent deflection. They commonly have a 30° helix angle.
Male Diamond Knurling Wheels
Used for forming female diamond knurling patterns. Like female wheels, they usually have a 30° helix angle.
Standard (Straight) Knurling Wheels
Create a straight knurling pattern. Also known as straight, these wheels do not have a helix angle.
Pitch Systems:
There are two pitch systems for specifying tooth spacing on a knurl wheel:
Circular Pitch measures the distance from one tooth point to the next along the wheel’s circumference, typically expressed in teeth per inch (TPI).
Diametral Pitch refers to the number of teeth per inch of the wheel’s diameter. This system is designed for accurate tracking on standard fractional-sized blanks.
Determining Blank Diameter and Number of Teeth Rolled
To calculate the appropriate blank diameter or the number of teeth that will be formed, different formulas apply depending on whether you're using circular pitch or diametral pitch knurls.
For Diametral Pitch Knurls:
Use these simpler equations:
Blank Diameter
Blank Dia. = # Teeth [part] / D.P. of Knurl
Teeth on Part
Teeth # Teeth [part] = Blank Dia. x D.P. of Knurl
Diametral pitch knurls are designed to permit accurate tracking on standard fractional-sized blanks. This makes choosing a blank diameter easier. Due to the Tracking Correction Factor (C.F.), choosing a blank diameter for circular pitch knurls is a bit more difficult and usually involves experimentation. This correction factor takes into account the fact that the tips of the knurl’s teeth will penetrate below the blank’s diameter by the end of the first revolution.
For Circular Pitch Knurls:
Use the following formulas:
Blank Diameter Blank Dia. = (# Teeth [part] / # Teeth [die]) x (Knurl Dia. + C.F.*)
TPI | *Approximate Value of C.F. (In.) |
12-19 | 0.010 |
20-29 | 0.007 |
30-39 | 0.005 |
40-49 | 0.003 |
50-80 | 0.002 |
*Note: The C.F. varies with feed rate, blank hardness, and the diameters of the knurl and blank. Circular pitch knurling often requires some trial and error to fine-tune the blank diameter due to this variable.
Standard Materials:
• Cobalt: Offers excellent hardness and superior wear resistance compared to standard high-speed steel. Cobalt knurling tools are ideal for working with high-tensile alloys and tough materials.
• High Speed Steel (HSS): Provides good wear resistance and is a reliable option for general-purpose knurling across both ferrous and nonferrous materials.
• Powdered Metal (PM): Combines toughness with cost-effectiveness. PM knurling tools are suitable for abrasive applications, such as knurling on high-silicon aluminum or other hard alloys.
Knurling Holders:
Bump Knurlers are used to hold knurl wheels that form a pattern or gripping surface on small to medium-sized workpieces. Ideal for use on steel, brass, aluminum alloys, and plastics.
Cut Knurlers hold knurl wheels to cut a pattern or gripping surface on medium- to large-sized workpieces. They are used at higher speeds than bump knurlers. Ideal for creating sharp corners on softer materials.
Scissor & Straddle Knurlers are designed to clamp opposing knurl wheels. These self-centering tools are easily adjustable via built-in pins and screws that maintain alignment. Excellent for more complex or demanding knurling operations.
Internal Knurlers enter the workpiece radially. Once the desired depth is reached, the knurling pattern is formed after several revolutions.
End-Rolling Knurlers enter a workpiece axially. The depth of the knurl wheel must be set before making contact with the workpiece.