Technical Guide
5 min read
Knurling Types for CNC Turned Components: A Specification Guide
A practical guide to knurling patterns used on precision turned components. Covers straight, diamond, helical, and custom knurl types, material compatibility, and how to specify knurling on drawings.
Knurling is a surface texturing operation performed during CNC or conventional turning that creates a regular raised pattern on the component's outer diameter. It serves two primary functions: improved grip for manual handling or tightening, and mechanical retention when the knurled surface is pressed into a mating bore (as in moulding inserts or press-fit bushes).
Knurling Pattern Types
| Type | Pattern | Best Use |
|---|---|---|
| Straight (Parallel) | Longitudinal lines parallel to the axis | Grip for hand-tightened components; axial retention in press-fits |
| Diamond | Crosshatch at 30° or 45° angles — most common type | General grip; press-fit retention (resists both axial and rotational pull-out) |
| Helical | Spiral lines at an angle to the axis (left or right hand) | Components needing directional grip; decorative knurling |
| Checkered | Alternating raised squares at 90° | Decorative applications; grip handles and knobs |
| Raised (Form knurl) | Raised profile pressed into the material | Standard for moulding inserts; creates displaced material peaks |
| Cut Knurl | Material cut away to form the pattern — not displaced | Hard materials (SS, carbon steel) where form knurling causes work-hardening issues |
| Coarse / Medium / Fine | Pitch designation: coarse (0.8–1.6 mm), medium (0.5–0.8 mm), fine (<0.5 mm) | Coarse for grip; fine for small components or decorative finish |
| Concave / Convex | Pattern on curved or profiled diameter sections | Speciality components, surgical instruments, custom grips |
| Micro Knurl | Very fine pitch — typically under 0.3 mm | Precision instruments, medical devices, small electrical contacts |
| Custom Pattern | Multi-start, left-hand, or proprietary designs | Aerospace, medical, proprietary retention applications |
Knurling Standards
- DIN 82 — Knurling (German standard; widely referenced internationally)
- ISO 13444 — Knurling of straight, diagonal, and crossed diamond patterns
- ASME B94.6 — Knurls and Knurling (US standard)
- On drawings, specify: type (e.g., diamond), pitch (e.g., 0.8 mm), depth, and standard reference
Material vs Knurling Compatibility
| Material | Preferred Knurling Types | Notes |
|---|---|---|
| Brass | Diamond, Fine, Straight | Soft and ductile — form knurling works well; excellent definition |
| Stainless Steel | Cut Knurl, Fine Diamond | Work-hardens under pressure; cut knurling preferred over form knurling |
| Mild Steel | Coarse Diamond, Straight | Good for form knurling; coarser pitch gives better grip |
| Aluminium | Fine Diamond, Straight | Soft material — fine pitch avoids tearing; sharp tooling required |
| Copper | Fine, Straight | Very soft; fine pitch and light pressure prevent material smearing |
How to Specify Knurling on a Drawing
- Pattern: e.g., 'Diamond knurl' or 'Straight knurl'
- Pitch: e.g., '0.8 mm pitch' (distance between adjacent ridges)
- Depth: e.g., '0.4 mm depth' (or specify 'to standard')
- Length and position: define the knurled zone with dimensions — do not leave it undefined
- Standard reference: e.g., 'Knurl per DIN 82' or 'per ISO 13444'
Note that form knurling increases the effective outer diameter of the component — the raised material creates a larger OD than the pre-knurl diameter. Account for this in mating bore specifications, especially for press-fit applications.
Knurling for Moulding Inserts
Brass moulding inserts use knurling as the primary retention mechanism in plastic. Diamond knurling is the most common choice because it resists both axial pull-out and rotational torque-out forces. The knurl pitch and depth are sized relative to the insert OD and the target plastic material — finer pitches for small inserts, coarser pitches for larger ones where greater surface engagement is needed.
Frequently Asked Questions
What is the most common knurling pattern for industrial components?
Diamond knurling is the most widely used pattern. It provides resistance in both the axial and rotational directions, making it suitable for hand-grip components, moulding inserts, and press-fit parts. Straight (parallel) knurling is used where only axial retention is needed or for a cleaner visual appearance.
What is the difference between form knurling and cut knurling?
Form knurling displaces material — the knurl wheel presses into the surface and pushes metal to form peaks and valleys. Cut knurling removes material with a cutting tool. Form knurling works well on soft materials like brass, aluminium, and mild steel. Cut knurling is preferred for harder materials like stainless steel, where the pressure required for form knurling would cause work-hardening and tool damage.
Does knurling change the diameter of the component?
Yes. Form knurling raises material above the original surface, increasing the effective outer diameter. The increase depends on pitch and material. This must be accounted for when designing press-fit joints or mating bores. Cut knurling reduces the diameter slightly. Specify the final knurled diameter (or the pre-knurl diameter plus the expected increase) on the drawing.