Knurling wheels, also known as a knurling die, are used to create a pattern or gripping surface on a cylindrical blank. They are used on steel, brass, aluminum alloys and hard plastics. Knurls have V-shaped teeth that deform, displace or push the material rather than cut it. The embossed patterns can be decorative, but more often act as hand grips and are commonly seen on handles, knobs or rollers. Diagonal, diamond and straight are the three most common patterns generated by knurling wheels. Knurling Wheel Sets are also available.
Diagram of a Knurl Wheel
Basic Tips:
- Ensure knurl's axis is parallel to the blank’s axis
- Never over roll. Try to limit the pattern to only about 90% full
- Increase the feed rate in the 1st revolution. Forming a deeper, wider impression the first time around helps to assure that the teeth will track into the initial grooves for all subsequent revolutions
Form and Cut Type:
- Cut type knurl wheels produce textured patterns by cutting into and removing material from the workpiece. They reduce the diameter of the workpiece as the pattern is applied. Cutting knurls are ideal for medium to larger sized workpiece diameters.
- Form knurl wheels produce textured patterns by forming an impression. This process displaces the material and increases the diameter of the workpiece. Form knurling is ideal for smaller to medium sized workpiece diameters.
Standard, also known as straight, knurl wheels have sharp corners on the leading edge. They are used where heavy loading is required.
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 knurls have a sharp leading edge to spread out the loading. They provide a smooth and precise finish.
Left-hand diagonal knurl wheels are designed to produce right-hand diagonal patterns. On a two-wheel knurling tool, left- and right-diagonal wheels are used together to create a diamond design. They commonly have a 30° left hand helix angle.
Right-hand diagonal knurl wheels are used to produce left-hand diagonal patterns. On a two-wheel knurling tool, left- and right-hand diagonal wheels are used together to create a diamond design. They commonly have a 30° right hand helix angle.
Female diamond knurl wheels are used to create a male diamond knurl pattern. They are used to create a raised diamond design. 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 knurl wheels are used to create a female diamond knurl pattern. They commonly have a 30° helix angle.
Standard, also known as straight, knurl wheels are used to create a straight knurl pattern. They do not have a helix angle.
Diamond Pattern Tip:
Traversing is not recommended when using diamond knurls. If a longer knurl pattern is required, left- and right-hand diagonal knurls should be used.
Pitch Systems:
There are two pitch systems for specifying tooth spacing on a knurl.
- Circular pitch is based on the distance between the teeth per inch (TPI). It is measured along the wheel from one tooth point to the next.
- Diametral pitch is based on the number of teeth per inch of the wheel’s diameter. They are designed to permit accurate tracking on standard fractional sized blanks.
Determining Blank Diameter and the Number of Teeth that will be Rolled
For Circular pitch knurls:
Blank Dia. = (# Teeth [part] / # Teeth [die]) x (Knurl Dia. + C.F.*)
Or
# Teeth [part] = (Blank Dia. x # Teeth [die]) / (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 |
For Diametral pitch knurls:
Blank Dia. = # Teeth [part] / D.P. of Knurl
Or
# 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.
Cobalt is harder than high speed steel and provides better wear resistance. It is commonly used on high tensile alloys.
High Speed Steel (HSS) provides good wear resistance and can be used in general-purpose applications for both ferrous and nonferrous materials.
Powdered Metal (PM) is tougher and more cost effective than solid carbide. It is commonly used on highly abrasive materials including high silicon aluminums.
Knurling Holders:
Bump Knurlers are used for holding knurl wheels to form a pattern or gripping surface on small- to medium-sized workpieces. Ideal for used on steel, brass, aluminum alloys and plastics.
Cut Knurlers are used for holding 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/hold a pair of opposing knurls. They are self-centering can be easily adjusted due to having a set of pins and screws to help keep the knurls on the holder. Ideal for more difficult operations.
Internal Knurlers are used for entering a workpiece radially. Once the knurl wheel has reached the depth, it will take several revolutions to complete the knurling operation.
End-Rolling Knurlers are used for entering a workpiece axially. The depth of the knurl wheel must be set before the wheel reaches contact with the workpiece.
