BIZOMAT MAKEOS · Gears
Gear Hobbing Cycle Time
How long does it take to hob this gear at the chosen hob speed and feed?
Hobbing time for a spur or helical gear from the number of teeth, hob starts, hob diameter and cutting speed, axial feed per work revolution, face width, helix angle, full-depth approach and overrun, for one gear or a stack.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Number of teeth in the gear | Teeth in the gear being cut. | |
| Hob starts | Number of threads on the hob. | |
| Hob outside diameter | mm | Outside diameter of the hob. |
| Cutting speed | m/min | Hob cutting speed for the tool and material. |
| Axial feed per work revolution | mm/rev | Axial feed of the hob per revolution of the work. |
| Face width (of the stack) | mm | Total face width of the gears cut in one pass. |
| Whole depth of tooth | mm | Whole depth of the tooth (about 2.25 × module). |
| Helix angle (0 = spur) | ° | Helix angle of the gear. |
| Overrun | mm | Run-out beyond the face. |
| Gears in the stack | Number of gears cut together. | |
| Load and unload time per stack | min | Handling time per cycle. |
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: Number of teeth in the gear
- What it is
- The number of teeth being cut on the gear blank.
- Units and format
- Enter a plain number with no unit. The form accepts 4 to 2000. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The work speed falls in proportion, so the cutting time rises in proportion.
What this means: Hob starts
- What it is
- The number of threads (starts) on the hob; each hob revolution moves the work round by this many teeth.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 10. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The cutting time is inversely proportional to the number of starts.
What this means: Hob outside diameter
- What it is
- The outside diameter of the hob, which turns the cutting speed into hob rpm and sets the approach distance needed to reach full depth.
- 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 80 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Cutting speed
- What it is
- The surface speed at the outside diameter of the hob, chosen for the hob material and the gear material.
- Units and format
- Enter a number in m/min: metres per minute. The form accepts 0.000001 m/min to 2000 m/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 m/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The cutting time is inversely proportional to it.
- Get it right
- Take it from the hob supplier’s data for your materials.
What this means: Axial feed per work revolution
- What it is
- The distance the hob moves along the gear axis for each revolution of the work.
- Units and format
- Enter a number in mm/rev: millimetres per revolution. The form accepts 0.000001 mm/rev to 50 mm/rev. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.5 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 cutting time is inversely proportional to the feed.
- Get it right
- It is per work revolution, not per hob revolution.
What this means: Face width (of the stack)
- What it is
- The total face width cut in one pass: the face of one gear, or the combined width of all gears in the stack.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 5000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- For a stack, add up the faces of all the blanks; the number in the stack only divides the time.
What this means: Whole depth of tooth
- What it is
- The whole depth of the gear tooth, from tip to root, which sets how far the hob must travel to reach full depth before the face.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5.625 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Helix angle (0 = spur)
- What it is
- The helix angle of the teeth of a helical gear; zero for a spur gear. It lengthens the hob travel across the face.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0° to 60°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Overrun
- What it is
- The extra axial travel beyond the face so that the hob completely clears the gear at the end of the cut.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 500 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Gears in the stack
- What it is
- The number of gear blanks mounted together and cut in one pass; times are reported per gear.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 100. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Set the face width to the total of the stack as well, or the time per gear will be understated.
What this means: Load and unload time per stack
- What it is
- The handling time to load and unload one stack of blanks, shared among the gears in the stack for the floor-to-floor time.
- Units and format
- Enter a number in min: minutes. The form accepts 0 min to 1000 min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Method and formulas
- Hob speed n = 1000 V_c ÷ π D_h; work speed = n × starts ÷ z.
- Approach for full depth ≈ √[h (D_h − h)].
- Travel = b ÷ cos β + approach + overrun; time = travel ÷ (feed × work speed).
- Example: 40 teeth with a 1-start 80 mm hob take 5.9709 min to cut.
Limitations
- Single climb or conventional pass; roughing and finishing passes add time.
- Feeds and speeds come from your tooling supplier and machine.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Quote gear cutting time
- Compare single- and multi-start hobs
- Balance hobbing with other operations
Who it is for
- Gear manufacturing engineers
- Estimators
- Machinists
What you get
- Hob and work speeds
- Cutting time per gear
- Floor-to-floor time per gear
Interpreting the result
- A two-start hob halves cutting time but coarsens the feed marks; check the finish needed.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3347–3349. Topic reference; no source tables or recommended settings are reproduced.
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