BIZOMAT MAKEOS · Threads
Thread Rolling Set-up (Blank Diameter, Roll Size, Starts)
For rolling this metric thread with cylindrical dies, what blank diameter do I turn, how many starts must the rolls have to fit my machine, and what roll pitch diameter results?
Set-up for cylindrical-die thread rolling of an ISO metric thread: pitch diameter, thread height and stress area of the thread (as the metric thread tool), the blank diameter taken at about the pitch diameter, the roll pitch diameter and lead for the number of starts on the rolls (as the threading roll size tool), and the range of starts that gives a roll inside the machine’s roll diameter range.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Nominal diameter | mm | Nominal diameter of the metric thread. |
| Pitch | mm | Pitch of the thread. |
| Starts on the roll | Number of starts on each roll. | |
| Smallest roll pitch diameter for the machine | mm | Smallest roll pitch diameter the machine spindles accept. |
| Largest roll pitch diameter for the machine | mm | Largest roll pitch diameter the machine accepts. |
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: Nominal diameter
- What it is
- The nominal (major) diameter of the ISO metric external thread to be rolled, as in 12 for an M12 thread.
- 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 12 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 nominal diameter raises the pitch diameter and the roll pitch diameter for the same starts.
- Get it right
- Enter the thread’s nominal size, not the blank diameter; the tool works out the blank.
What this means: Pitch
- What it is
- The pitch of the thread: the axial distance from one thread crest to the next.
- 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 1.75 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A coarser pitch lowers the pitch diameter and increases the roll lead.
- Get it right
- Enter the pitch in millimetres, not threads per inch; fine-pitch threads have a smaller pitch than coarse ones.
What this means: Starts on the roll
- What it is
- The number of thread starts ground on each roll; a multi-start roll lets a roll much larger than the part roll a single-start thread.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 60. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 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 and roll lead rise almost in direct proportion to the number of starts.
- Get it right
- Choose a number in the range the tool reports as fitting the machine.
What this means: Smallest roll pitch diameter for the machine
- What it is
- The smallest roll pitch diameter that the thread-rolling machine’s spindles and slides can accept, from the machine manual.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the pitch-diameter limit for the rolls, not the bore of the roll.
What this means: Largest roll pitch diameter for the machine
- What it is
- The largest roll pitch diameter the thread-rolling machine can accept, from the machine manual.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 180 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- It must be larger than the smallest roll diameter.
Method and formulas
- Pitch diameter d₂ = d − 0.6495P; external thread height h₃ = 0.6134P; stress area from d₂ and d₃ (as the metric thread tool).
- Blank diameter ≈ pitch diameter, adjusted on trial for full form.
- Roll pitch diameter = N_s (d₂ − h₃ ÷ 2) − h₃; roll lead = N_s × P (as the threading roll size tool).
- Example: turn the blank to about 10.863 mm; 10-start rolls have a 102.19 mm pitch diameter; 8 to 17 starts fit the machine.
Limitations
- Blank diameter is a starting value; material flow and the class of fit set the final size.
- Cylindrical dies; flat dies and planetary heads use other relations.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set up a thread rolling machine
- Order thread rolls for a new thread
- Turn blanks for rolled threads
Who it is for
- Setters
- Manufacturing engineers
- Tool buyers
What you get
- Thread pitch diameter, height and stress area
- Blank diameter
- Roll pitch diameter, lead and suitable starts
Interpreting the result
- Rolls with more starts are larger and last longer, but must fit between the spindles.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2050–2051, 1867–1890. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Rolling threads: forming instead of cutting
In Yield and Plastic Flow by the Numbers
What it covers: How thread rolling forms a thread by plastic flow, why the blank is sized near the pitch diameter, how rolls and starts are chosen, and what rolling does for the thread's strength.
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Open the Thread Rolling Set-up (Blank Diameter, Roll Size, Starts) calculator