Knurling Diameter Calculator: Blank Size Before Knurling
Cold-formed knurling pushes metal up as well as cutting grooves, so the diameter after knurling is larger than the blank. This calculator estimates the blank to turn and finds a diameter that gives a whole number of teeth, which helps the knurl follow its own pattern.
Your numbers
Pitch is the distance between adjacent teeth on the knurl wheel.
Share of the tooth depth that shows as diameter growth. A rule of thumb, tune on scrap.
Your results
Knurling is a forming process and results depend on material, tool, feed and force. Use the output as a starting point and confirm on scrap before running parts.
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How to use it
Enter the outside diameter you want after knurling, choose the pitch of the knurl wheels in your holder and select a fill factor. Typical medium knurls have a pitch near one millimetre. The result gives the estimated diameter growth, a first blank, and a final blank adjusted to a whole tooth count. Turn the blank to the recommended diameter, knurl a sample and measure. Adjust the fill factor to match your material and tool so future jobs hit the target the first time.
- Pitch is printed on the wheel or holder
- Start with fill 0.6 and trim on scrap
- Measure the knurled diameter over the crests
Why a whole tooth count matters
On a freshly turned blank, the knurl wheel pushes its first impression and then follows the pattern as the work rotates. If the circumference is not an exact multiple of the pitch, the wheel meets the first mark out of step and creates a second set of teeth between the first, known as double tracking. Choosing a diameter with circumference equal to a whole number of pitches reduces that risk. The relation is simple: teeth equal pi times diameter divided by pitch.
Reading the results
The tooth depth is calculated from a 90 degree tooth, which is half of the pitch. The growth is a fraction of that depth because only part of the displaced metal rises above the original surface. The recommended blank is typically a few tenths of a millimetre below the target diameter, and the difference line shows how close the rounded tooth count lands to your goal. A large difference suggests choosing another pitch.
Common mistakes
A frequent error is machining the blank to the drawing diameter and then finding the knurled part oversize. Another is using the same blank for hard and soft materials, which behave differently. Also remember that cut knurling, which removes metal, does not grow the diameter the same way as forming.
- Do not use the finished diameter as the blank
- Check material hardness
- Allow for knurl tolerance on the drawing
Frequently Asked Questions
How much does knurling increase the diameter?
It depends on pitch, material and tool, but typically a few tenths of a millimetre for a medium pitch. Formed knurling raises the crests above the original surface, so the knurled outside diameter exceeds the blank.
What is double tracking in knurling?
Double tracking happens when the knurl wheel does not follow the first impression and creates a second, offset set of teeth, giving a rough pattern. A whole number of teeth around the circumference helps prevent it.
What pitch should I choose?
Fine pitches near 0.5 mm suit small, decorative or tactile parts, medium near 1.0 mm is common for hand grips, and coarse 1.6 mm suits large diameters. Choose by diameter and the feel required.
Does this apply to cut knurling?
Not fully. Cut knurling removes material and gives less growth, so the blank is closer to the final size. Use the fill factor of 0.5 or lower and verify on scrap.
If special process notes like knurl pitch and blank size are kept in routings, we can help bring them into your ERP so every shift sees the same instruction.
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