Guide to knurling on the lathe
Knurling is a metalworking process used to create a patterned texture on cylindrical surfaces, often for grip or aesthetic purposes. It’s done on a lathe using a knurling tool, which displaces material rather than cutting it. Here’s a structured guide to knurling tools and their use on the lathe.
1. Knurling Basics
Knurling produces a regular crosshatch, straight, or diagonal pattern by pressing hardened rollers into the rotating workpiece. It’s typically used on handles, knobs, and tool grips.
Knurl patterns include:
Straight: lines parallel to the axis
Diagonal (left/right-hand): lines at ~30° to axis
Diamond: intersecting diagonals
2. Types of Knurling Tools
A. Bump-Type (Conventional)
Holds one or more knurl wheels on a rigid arm.
Presses the wheel into the workpiece from one side.
Suitable for small-diameter workpieces.
Can induce deflection or chatter on unsupported or flexible parts.
B. Scissor-Type (Clamp-Type)
Holds knurl wheels on opposing arms, clamping the part.
Distributes force evenly, reducing deflection.
Better for larger diameters or thin-walled tubing.
More stable and easier to control pattern quality.
C. Cut-Type
Wheels are angled and sharp, cutting rather than deforming.
Requires precise setup and often used on CNC lathes.
Leaves cleaner knurl patterns with less material displacement.
Not widely used in manual operations.
3. Knurl Wheels
Knurl wheels are replaceable and vary by:
Pitch: Coarse, medium, fine (e.g. 16, 21, 33 TPI)
Pattern: Straight, diagonal, diamond
Width and Diameter: Must match tool spec
Material: Typically HSS or carbide
Proper pitch selection is critical to avoid double-tracking (a misaligned, fuzzy pattern). Use pitch charts or calculate based on diameter and feedrate to avoid mismatch.
4. Setup and Operation
A. Lathe Preparation
Secure the workpiece rigidly, with tailstock support if needed.
Choose a suitable speed: typically 50–200 RPM.
Apply cutting fluid generously to reduce friction and improve finish.
B. Tool Positioning
Align knurl wheel axis perpendicular to workpiece axis.
For scissor-type, ensure even pressure from both wheels.
For bump-type, apply force progressively to avoid excessive strain.
C. Engaging the Knurl
Feed tool into the workpiece until pattern fully develops.
Maintain constant depth and pressure once started.
Knurling occurs rapidly—don’t dwell after the pattern is complete.
D. Feedrate
Slow, steady longitudinal feed is key (manual or power).
Avoid stopping during the pass to prevent pattern irregularities.
5. Tips and Troubleshooting
| Problem | Cause | Solution |
|---|---|---|
| Double tracking | Workpiece diameter not matched to pitch | Use knurl pitch charts or adjust diameter |
| Poor definition | Low pressure, worn wheel | Increase force, replace wheel |
| Chatter/vibration | Tool deflection, high speed | Use scissor-type, reduce RPM |
| Incomplete pattern | Too fast feed or shallow engagement | Reduce feedrate or increase pressure |
6. Example Workflow (Diamond Knurl on 1" Mild Steel Rod)
Mount a scissor-type tool with medium-pitch diamond wheels.
Set spindle speed to 100 RPM.
Apply cutting oil.
Center the tool on the rod; clamp with moderate pressure.
Feed in manually until a full pattern appears.
Engage power feed at ~0.005–0.01 in/rev.
Once the full length is knurled, retract and inspect.