BIZOMAT MAKEOS · Manufacturing
Rotary Axis Feed Plan (Inverse-Time Feed and Axis Rate Limits)
For this combined linear and rotary move, what inverse-time feed gives my cutter feed, do the rotary and linear axes stay within their rate limits, and what feed is actually achievable?
Feed plan for a 4th-axis or rotary-table move: arc length at the cutting radius, path length at the cutter, block time and inverse-time F value for the wanted feed (as the inverse time feed tool), the rotary rate in degrees per minute and the linear axis rate, checked against the machine’s axis rate limits, with the largest achievable cutter feed and its inverse-time value if a limit governs.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Move | choice | Kind of move. |
| Linear length of the move | mm | Linear travel of the move. |
| Rotary angle of the move | ° | Rotation of the move. |
| Cutting radius on the rotary axis | mm | Radius on the part where the cutter works. |
| Wanted feed at the cutter | mm/min | Feed you want at the cutter. |
| Machine limits | ||
| Largest rotary axis rate | °/min | Highest rate the rotary axis can move at in feed moves. |
| Largest linear axis feed | mm/min | Highest feed the linear axis allows. |
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: Move
- What it is
- The kind of move being programmed: a combined linear and rotary move, a rotary move with the cutter at a radius, or a plain linear move.
- Units and format
- Choose one of 3 options from the list: Combined linear and rotary; Rotary move at a radius; Linear move.
- Example
- The form opens with “Combined linear and rotary” selected as a worked example. Choose the option that matches your case.
- Get it right
- In rotary mode the linear length is ignored; in linear mode the angle and radius are ignored.
What this means: Linear length of the move
- What it is
- The straight-line travel of the linear axis or axes during the move, from the CNC program.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10000000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Ignored in rotary mode. Enter the linear travel only, not the path at the cutter.
What this means: Rotary angle of the move
- What it is
- The rotation of the rotary axis during the move, from the CNC program.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0° to 1000000°. 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 larger angle lengthens the arc and the block time; in a combined move it also raises the rotary axis rate.
- Get it right
- Ignored in linear mode. Enter the incremental rotation of this block, not the absolute end position.
What this means: Cutting radius on the rotary axis
- What it is
- The radius from the rotary axis centre to the point where the cutter works on the part, which turns the rotation into an arc length.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 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 radius lengthens the arc, giving a longer block time and a lower rotary rate for the same feed.
- Get it right
- Use the radius at the cutting point, not the stock or table radius. Ignored in linear mode.
What this means: Wanted feed at the cutter
- What it is
- The feed you want at the cutter along its path through the part, from your cutting data.
- Units and format
- Enter a number in mm/min: millimetres per minute. The form accepts 0.000001 mm/min to 1000000 mm/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 300 mm/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The inverse-time F value and both axis rates rise in direct proportion to the wanted feed.
- Get it right
- This is the feed at the cutter, not the rotary axis rate in degrees per minute.
Machine limits
What this means: Largest rotary axis rate
- What it is
- The highest rate the rotary axis can move at in feed moves, from the machine or rotary table specification.
- Units and format
- Enter a number in °/min: °/min. The form accepts 0.000001 °/min to 10000000 °/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2000 °/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the feed-move limit, not the rapid traverse rate.
What this means: Largest linear axis feed
- What it is
- The highest feed the linear axes allow in cutting moves, from the machine specification.
- Units and format
- Enter a number in mm/min: millimetres per minute. The form accepts 0.000001 mm/min to 10000000 mm/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10000 mm/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the maximum cutting feed, not the rapid traverse rate.
Method and formulas
- Arc = π r × angle ÷ 180; path = linear, arc or √(linear² + arc²); block time = path ÷ feed; F = 1 ÷ time (as the inverse time feed tool).
- Rotary rate = angle ÷ time; linear rate = distance ÷ time.
- Achievable feed = wanted feed × the smallest of 1, rotary limit ÷ rotary rate and linear limit ÷ linear rate.
- Example: program F3.7361 (inverse time); the rotary axis turns at 336.25 °/min, within its 2000 °/min limit.
Limitations
- Constant feed through the block; acceleration at block ends is not included.
- Cutting radius taken as constant over the move.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Program a wrapped or helical rotary move
- Check a rotary feed against the axis limit
- Find why a rotary move runs slower than programmed
Who it is for
- CNC programmers
- Machinists
- Manufacturing engineers
What you get
- Path length, block time and inverse-time F
- Rotary and linear axis rates
- Achievable feed
Interpreting the result
- Near the centre of rotation the rotary rate limit rarely matters; far out it often sets the feed.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1288–1289. Topic reference; no source tables or recommended settings are reproduced.
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Open the Rotary Axis Feed Plan (Inverse-Time Feed and Axis Rate Limits) calculator