BIZOMAT MAKEOS · Threads
Threading Roll Pitch Diameter
What pitch diameter should a single- or multiple-start threading roll have for this screw thread?
Pitch diameter of a threading roll for a screw machine from the pitch diameter of the thread to be rolled, the single depth of thread and the number of starts on the roll, by the handbook formula, with the roll lead.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Pitch diameter of the screw thread | mm | Pitch diameter of the thread to be rolled. |
| Single depth of thread | mm | Single depth of the thread form. |
| Starts on the roll | Number of single threads (starts) on the roll, chosen to give a convenient roll diameter. | |
| Thread pitch | mm | Pitch of the screw thread. |
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: Pitch diameter of the screw thread
- What it is
- The pitch diameter of the screw thread to be rolled on the work, the diameter at which the thread and the groove between threads are equally wide.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 11.43 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The roll pitch diameter rises by the number of starts for each millimetre added here.
What this means: Single depth of thread
- What it is
- The single depth of the thread form: the radial height from crest to root on one side of the thread.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 50 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.2675 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Starts on the roll
- What it is
- The number of starts (single threads) on the threading roll, chosen to give a roll diameter that suits the screw machine.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 20. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The roll lead rises in proportion and the roll pitch diameter nearly so.
What this means: Thread pitch
- What it is
- The pitch of the screw thread being rolled, the distance between adjacent threads along the axis; it is used only for the roll lead.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 50 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.954 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- For inch threads, pitch = 25.4 ÷ threads per inch.
Method and formulas
- D = N (d − T ÷ 2) − T, as in the handbook (a double roll for a ½-in. thread with d = 0.4500 in and T = 0.0499 in gives about 0.800 in).
- Roll lead = N × thread pitch, so the helix angles of roll and work nearly match.
- Example: a 2-start roll for a 11.43 mm pitch diameter needs a 20.325 mm pitch diameter.
Limitations
- One screw machine maker’s recommendation; follow the roll supplier where it differs.
- Single-start roll for external threads on screw machines.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Specify a threading roll for an automatic screw machine
- Choose the number of starts for a practical roll diameter
- Check a supplied roll against the thread
Who it is for
- Screw machine setters
- Tooling engineers
- Machinists
What you get
- Roll pitch diameter
- Roll lead
- Roll diameter ratio
Interpreting the result
- Add starts to obtain a larger, stronger roll that still matches the work’s helix angle.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2050–2051. Topic reference; no source tables or recommended settings are reproduced.
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