A knurling tool on a CNC lathe pushes a hard patterned wheel into a spinning part. The goal is a grip surface with a straight line, a diagonal cut, or a diamond layout. You get good results when a few details are nailed down. They are the right tool for the work, a pitch that matches the part size, the wheel set at the correct centre height, the wheel kept square to the surface, enough starting depth, and a low spindle speed with a steady feed. When knurls turn out badly, it is usually from setup issues, not the machine. The next sections explain how to get each item correct.
What a Knurling Tool Does on a CNC Lathe
Knurling puts a texture onto a round surface. That texture helps with grip and also with turning or pressing parts together. Common uses are knobs, handles, tool grips, and the shaft ends that get pressed into a mating piece.
On a CNC lathe, the toolpath can look easy. The cycle goes to the start point, runs along the knurl length, then pulls back. But that simple motion hides a big fact. The CNC repeats the same moves every time. So if the wheel is a little off-centre, or the wheel is worn, the same problem shows up on every part. Because of that, focus on the tool, the pitch, and the setup more than the code.
Form Knurling vs Cut Knurling: Which Should You Use?
Form knurling, also called roll knurling, presses the pattern into the surface and displaces metal. Cut knurling uses wheels that shear the pattern and remove some material as chips. Both are used on CNC lathes.
|
Form (roll) knurling |
Cut knurling |
|
|
How it works |
Wheels press and displace material |
Wheels cut the pattern and produce chips |
|
Radial force on the part |
Higher |
Generally lower |
|
Effect on diameter |
Finished outside diameter ends up larger than the turned blank |
Diameter changes less, because material is removed |
|
Best for |
General production on rigid setups |
Thin-wall, slender or less rigid parts |
|
Watch for |
Deflection of long parts |
Chips caught in the pattern, so flush well |
If the knurled diameter has a tolerance, for example, for a press fit, run a trial piece and measure over the ridges with a micrometer before you start production.
Types of Knurling Tools for CNC Lathes
The tool type decides how the cutting force is carried, so it matters as much as the wheel.
|
Tool type |
How it works |
Where it fits |
|
Bump (push) type |
One or two wheels pressed radially against the work; a pivot head lets the wheels self-align |
General lathe work where the part and machine are rigid |
|
Scissor type |
Two opposed wheels clamp the part, so the radial forces largely cancel |
Longer or slender parts and lighter machines |
|
Clamp or V-clamp type |
Compact two-wheel head with an adjustment knob |
Small diameters, for example the 3 to 20 mm range |
|
Fixed-head CNC holders |
Rigid holders for single, double, face, internal or cut knurling |
Repeat production on CNC turrets |
|
Rotating or multi-head holders |
Several wheel pairs on one head |
Changing pitch without swapping the whole tool |
On the Jaibros knurling tools range, you will find bump-type pivot head tools, a scissor-type holder with 1/16 to 2-1/4 inch capacity, V-clamp tools for 5 to 20 mm work, and face, internal and cut-knurling holders for CNC turning. For a deeper look at holder designs, see our guide to knurling tool types in CNC turning. Check the shank size against your turret or turning sleeve before ordering.
How to Choose the Knurl Pattern and Pitch
The pattern follows the job:
|
Pattern |
Look |
Typical use |
|
Straight (axial) |
Parallel lines along the axis |
Press-fit shaft ends, knobs turned by fingertips |
|
Diamond (cross) |
Crossed diagonal pattern from a left-hand and right-hand wheel pair |
Handles, tool grips, general grip surfaces |
|
Right or left diagonal |
Angled lines in one direction |
Grip and decorative surfaces |
Pitch is the distance between neighbouring ridges. Sets commonly come in fine, medium and coarse pitches, for example 0.5, 1.0 and 1.5 mm. As a general rule, use finer pitches on small diameters and thin walls, medium for everyday handles and knobs, and coarser pitches on larger diameters where you want a more aggressive grip. Spare wheels are sold in pairs, such as these diamond medium pitch knurls and straight-pattern knurls. Always replace a pair together.
Match the diameter to the pitch. Double tracking happens when the wheel's teeth do not track into the same grooves on subsequent revolutions. While calculated blank diameter plays a role, double tracking on a CNC lathe is most effectively prevented by engaging the knurling wheel to full penetration depth quickly on the very first turn so the teeth firmly register into the metal. Always confirm your setup on a test piece, as metal displacement during form knurling naturally expands the outer diameter.
How to Choose a Knurling Tool for a CNC Lathe by Material
|
Material |
What to expect |
Practical advice |
|
Mild steel (for example EN8) |
Forms well and holds a crisp pattern |
Form knurling with moderate pressure is the usual choice |
|
Stainless steel |
Work-hardens and needs high force |
Use a rigid tool, well-lubricated, with sharp wheels in good condition; consider cut knurling if the setup is not stiff |
|
Aluminium |
Forms easily but deforms or flakes under excess pressure |
Use light depth and support thin walls |
|
Brass and copper |
Clean pattern at relatively low force |
Keep wheels clean so chips do not get pressed in |
Part shape matters as much as material. A slender part can flex under the radial load, so support it with a tailstock revolving centre or steady rest, or switch to a scissor-type tool.
How to Knurl on a CNC Lathe: Step-by-Step
- Prepare the blank. Turn to the planned diameter, allowing for growth in form knurling, and add a lead-in chamfer so the wheel starts cleanly.
- Mount the holder rigidly. Keep overhang short, seat the shank fully, and tighten it properly.
- Set centre height. The wheel axis should sit on the spindle centreline and be square to the work. Scissor tools centre themselves, but still check them.
- Support the part. Use a revolving centre for any part that could flex.
- Set a low, fixed spindle speed. A fixed rpm (G97) is simpler and more predictable here than constant surface speed. Follow the toolmaker's guidance and start low. The formula is rpm = 1,000 × surface speed ÷ (π × diameter).
- Engage to full depth rapidly on the first revolution. Plunge the wheel radially to full depth within the first turn so the teeth seat cleanly into the workpiece and lock the pattern pitch before starting the axial feed. This prevents double-tracking overlap.
- Feed along the length. Use a steady feed and flush with cutting oil or coolant so chips do not get pressed into the pattern.
- Check the first part. Compare with a master or sample, measure the diameter over the ridges, then store the working depth in a dedicated tool offset so it does not depend on the operator.
Why Does My Knurl Double Track? Common Problems and Fixes
|
Symptom |
Likely cause |
What to try |
|
Double tracking (overlapping patterns) |
Diameter does not match the pitch; not enough depth at the start; loose wheel |
Adjust blank diameter or pitch, engage to full depth first, check wheel play on its pin |
|
Shallow or incomplete pattern |
Too little depth, worn wheels, pitch too coarse for the diameter |
Increase depth, replace the wheel pair, use a finer pitch |
|
Flaking or torn ridges |
Chips or debris pressed in, too much depth, poor lubrication |
Flush well, clean the wheels, reduce depth |
|
Pattern fades along the length |
Part deflection, tool not square |
Add support, re-check alignment and centre height |
|
Chatter or ripple marks |
Spindle speed too high, long overhang, loose holder |
Lower rpm, shorten overhang, tighten the holder |
|
Diameter out of tolerance after knurling |
Growth in form knurling |
Allow for it and verify with a trial piece |
Inspecting and Maintaining Tools
Inspect the wheels for chipped or rounded teeth and check that they spin freely without side play on their pins. Clean the teeth with a brush after use, because packed chips cause flaking on the next part. Keep wheel pairs matched in pitch and hand, and replace worn wheels before the pattern starts to degrade. For inspection, use a micrometer from the measuring instruments range to check the diameter over the ridges, and compare the pattern against a master sample under good light.
Frequently Asked Questions
What is the difference between form knurling and cut knurling?
Form knurling presses the pattern in and displaces material, so the finished diameter grows slightly. Cut knurling shears the pattern and removes material, which usually needs less radial force and suits thin or slender parts.
Which knurling is best for a CNC lathe?
It depends on the part. Rigid fixed-head holders suit repeat production on a CNC turret. Scissor-type tools suit longer or slender parts because the forces are balanced. Clamp-type tools suit small diameters. Match the holder shank to your turret and the capacity to your part diameter.
How do I stop double tracking?
Ensure rapid radial penetration to full depth on the very first part revolution so the wheel's teeth immediately track into the metal. Also verify that the tool holder is completely rigid, the wheel spins freely on its pin without excessive side play, and the blank diameter is roughly suited for the chosen pitch.
What knurl pitch should I use?
Use finer pitches on small diameters and thin walls, medium pitch for general handles and knobs, and coarse pitches on larger diameters where grip matters most. Common pitches in sets are 0.5, 1.0, and 1.5 mm.
What spindle speed and feed should I use for knurling?
There is no single value. Use a low, fixed spindle speed and a steady feed, following the knurl maker's recommendation for your material, and adjust from a trial piece. If the pattern chatters, lower the speed before changing anything else.
Conclusion
Getting a good knurling tool for a CNC lathe is only half the job. The other half is matching the tool type and pitch to the part, setting the wheel square on centre height, engaging to full depth, and checking the first piece before running a batch. Do that and the program will simply repeat a good result. To build your setup, browse the Jaibros knurling tools collection.