BIZOMAT MAKEOS · Manufacturing
Broach Tooth Pitch
What tooth pitch should this broach have for its chip space and machine capacity?
Minimum broach tooth pitch from chip space, allowable pitch from machine capacity, the pitch to use, and the number of teeth cutting at once.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Length of cut | mm | Length of the surface being broached in the cutting direction. |
| Depth of cut per tooth | mm | Rise per tooth (one side for round broaches), from broach design data for the material. |
| Chip space factor F | Chip space factor: about 3–4 roughing and 6 finishing for brittle materials; 4–7 roughing and 8 finishing for ductile materials. | |
| Width of cut | mm | Width of the layer removed by each tooth. |
| Broaching pressure | MPa | Pressure per unit area of cut (depth × width) for the material and depth, from broaching data tables. |
| Usable machine capacity (70% of maximum) | t | Usable capacity of the machine in metric tonnes, taken as 70% of its maximum to allow for dulling. |
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: Length of cut
- What it is
- The length of the surface being broached, measured in the direction the broach travels.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 220 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A longer cut raises the minimum pitch and puts more teeth in the cut.
- Get it right
- Use the length of the actual cut, not the length of the part if only part of it is broached.
What this means: Depth of cut per tooth
- What it is
- The rise per tooth: how much deeper each tooth cuts than the one before, on one side for round broaches, from the broach design data.
- 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 0.1 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 rise raises both the minimum and the allowable pitch.
- Get it right
- For round broaches this is the rise on one side, not the increase in diameter.
What this means: Chip space factor F
- What it is
- A factor that sizes the gullet between teeth to hold the curled chip, depending on whether the material is brittle or ductile and whether the teeth rough or finish.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 20. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger factor raises the minimum pitch.
- Get it right
- Take it from broach design data for your material and tooth type; ductile materials need more chip space.
What this means: Width of cut
- What it is
- The width of the layer each tooth removes, measured across the cutting edge.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 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 wider cut raises the allowable pitch based on machine capacity.
- Get it right
- For a keyway broach this is the keyway width; for a round broach use the circumference being cut.
What this means: Broaching pressure
- What it is
- The cutting force per square millimetre of chip area (depth times width) for this material and rise per tooth, from broaching data tables.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 100000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1586 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher pressure raises the allowable pitch based on machine capacity.
- Get it right
- Make sure the table value is converted to MPa; broaching data is often published in imperial units.
What this means: Usable machine capacity (70% of maximum)
- What it is
- The pulling or pushing force of the broaching machine that you can use, in metric tonnes, after reducing the maximum to allow for tooth dulling.
- Units and format
- Enter a number in t: tonnes. The form accepts 0.000001 t to 10000 t. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 t as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More capacity lowers the allowable pitch, allowing more teeth in the cut.
- Get it right
- Enter the reduced usable capacity, not the nameplate maximum; the label shows the reduction used.
Method and formulas
- Minimum pitch = 3√(L d F).
- Allowable pitch = d L b P ÷ (9810 T).
- Use the larger of the two; teeth in contact = L ÷ pitch (at least two are needed).
- Example (the handbook case for cast iron): minimum pitch 28.142 mm, allowable 33.345 mm, so use 33.345 mm.
Limitations
- Design data for rise per tooth and pressure must match the material; this tool does not supply them.
- Pitch is usually varied slightly between teeth to reduce chatter.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Lay out a new surface or internal broach
- Check whether a broaching machine has enough capacity
- Find teeth in contact for a part length
Who it is for
- Tool designers
- Manufacturing engineers
What you get
- Minimum pitch for chip space
- Allowable pitch for machine capacity
- Pitch to use
- Teeth cutting at once
Interpreting the result
- If fewer than two teeth cut at once, reduce the pitch or broach two parts together.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 980–990. Topic reference; no source tables or recommended settings are reproduced.
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