KEVOS® MAKEOS · Manufacturing
Top Knurling on an Automatic Screw Machine (Cam Rise and Revolutions)
When I top knurl from the cross slide of an automatic screw machine, how far must the knurl travel from first contact to the centre of the work, how much rise does that need on the cam, and how many spindle revolutions and how much time does it take at my feed?
Cross-slide (top) knurling on an automatic screw machine by the handbook method: the distance the knurl travels from first contact to the centre of the work at full tooth depth, c = √((R + r)² − (R + r − d)²) from the stock radius, the knurl radius and the depth of the teeth, which is the cam rise required; the revolutions to knurl at the feed per revolution, and the time at the spindle speed. The tooth depth can be entered or found from the circular pitch and included angle of a sharp V tooth.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Stock diameter | mm | Diameter of the bar stock being knurled; the formula uses the radius R. |
| Knurl diameter | mm | Outside diameter of the knurl; the formula uses its radius r. |
| Depth of teeth | choice | Find the depth of the teeth from the knurl’s circular pitch and tooth angle, or enter it. |
| Circular pitch of the knurl | mm | Circular pitch of the knurl teeth (25.4 ÷ diametral pitch for inch knurls; 32 pitch is 0.79375 mm). |
| Included angle of the teeth | ° | Included angle of the knurl teeth, for example 90° for brass as in the handbook example. |
| Depth of teeth (when entered) | mm | Depth of the knurled teeth, used when you enter it directly. |
| Machine | ||
| Knurling feed per revolution | mm/rev | Feed of the knurl per spindle revolution for top knurling, from your screw machine feed data. |
| Spindle speed | rpm | Spindle speed while knurling. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Stock diameter
- What it is
- Diameter of the bar stock being knurled on the screw machine.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 500 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7.9375 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger stock radius increases the cam rise a little.
- Get it right
- Use the turned diameter the knurl rolls on.
What this means: Knurl diameter
- What it is
- Outside diameter of the knurl used from the cross slide.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 200 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15.875 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger knurl increases the travel from contact to centre.
- Get it right
- Measure the knurl; resharpened knurls are smaller.
What this means: Depth of teeth
- What it is
- Whether the tooth depth is found from the knurl pitch or entered directly.
- Units and format
- Choose one of 2 options from the list: From circular pitch and tooth angle (sharp V); Entered directly.
- Example
- The form opens with “From circular pitch and tooth angle (sharp V)” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Chooses where the tooth depth comes from.
- Get it right
- Use the pitch for a standard sharp V knurl; enter the depth for special or worn knurls.
What this means: Circular pitch of the knurl
- What it is
- Circular pitch of the knurl, the distance between teeth around its face.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 20 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.79375 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The tooth depth grows with the pitch.
- Get it right
- For inch knurls it is π divided by the diametral pitch, or 25.4 divided by the teeth per inch.
What this means: Included angle of the teeth
- What it is
- Included angle of the knurl teeth.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 30° to 150°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 90° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A smaller angle gives deeper teeth for the same pitch.
- Get it right
- The handbook example uses 90° for brass.
What this means: Depth of teeth (when entered)
- What it is
- Depth of the knurled teeth when you enter it directly.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.4 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The cam rise grows roughly with the square root of the depth.
- Get it right
- Measure a knurled sample or take it from the knurl maker.
Machine
What this means: Knurling feed per revolution
- What it is
- Feed of the knurl per spindle revolution for top knurling.
- Units and format
- Enter a number in mm/rev: millimetres per revolution. The form accepts 0.000001 mm/rev to 5 mm/rev. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.127 mm/rev as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The revolutions to knurl fall in proportion as the feed rises.
- Get it right
- Take it from your screw machine feed table for the material.
What this means: Spindle speed
- What it is
- Spindle speed of the screw machine while knurling.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 20000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2400 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only moves the time to knurl.
- Get it right
- Use the speed set for the knurling position.
Method and formulas
- R = stock diameter ÷ 2; r = knurl diameter ÷ 2.
- Depth of a sharp V tooth d = circular pitch ÷ (2 tan(½ included angle)); for 90° teeth this is half the circular pitch.
- c = √((R + r)² − (R + r − d)²), the distance the knurl travels from first contact to the centre of the work.
- Revolutions = c ÷ feed per revolution; time = revolutions ÷ spindle speed.
- Example: a 15.875 mm knurl on 7.9375 mm stock with 0.39688 mm deep teeth needs a cam rise of 3.0485 mm, 24.004 revolutions at 0.127 mm/rev.
Limitations
- Inch or metric units may be used in the formula; this tool works in millimetres.
- The depth found from the pitch is that of a sharp V; worn knurls and rounded crests give a little less.
- Add any dwell revolutions you want at full depth, and the quick rise off centre, when laying out the cam.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Lay out the knurling lobe of a screw machine cam
- Find the revolutions and time a knurling operation adds to the cycle
- Compare knurling feeds
Who it is for
- Screw machine setters
- Cam designers
- Production engineers
What you get
- Depth of the teeth
- Travel from contact to centre, the cam rise required
- Revolutions to knurl
- Time to knurl
Interpreting the result
- A higher permissible feed shortens the knurling time in proportion; spiral knurling from the turret runs faster than diamond knurling.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1170. Topic reference; no source tables or recommended settings are reproduced.
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Open the Top Knurling on an Automatic Screw Machine (Cam Rise and Revolutions) calculator