BIZOMAT MAKEOS · Manufacturing
Circular Interpolation Feed
What tool-centre feed gives the specified feed around a circular wall?
Convert peripheral feed to tool-centre feed for a constant-height internal or external circular pass.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Machined feature | choice | Inside a bore or outside a boss. |
| Finished bore or boss diameter | mm | Finished wall diameter at the contact plane. |
| Cutter diameter | mm | Effective cylindrical cutter diameter; smaller than the bore for internal milling. |
| Specified peripheral feed | mm/min | Desired feed around the workpiece circumference after selecting suitable cutting data. |
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: Machined feature
- What it is
- Whether the cutter runs inside a round hole (bore) or around the outside of a round boss. It decides whether the tool centre path is smaller or larger than the finished wall.
- Units and format
- Choose one of 2 options from the list: Inside a circular bore; Around a circular boss.
- Example
- The form opens with “Inside a circular bore” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Inside a bore the centre feed is lower than the wall feed; around a boss it is higher.
- Get it right
- For a bore the centre path is the bore minus the cutter; for a boss it is the boss plus the cutter.
What this means: Finished bore or boss diameter
- What it is
- The finished diameter of the bore or boss wall that the cutter edge touches.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.001 mm to 1000000 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.
- Effect on the result
- Larger work diameters bring the centre feed closer to the peripheral feed.
- Get it right
- Use the finished size at the cutting plane, not a pre-drilled or rough size.
What this means: Cutter diameter
- What it is
- The effective cutting diameter of the end mill making the circular pass.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.001 mm to 1000000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 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 cutter lowers the centre feed inside a bore and raises it around a boss.
- Get it right
- For internal milling the cutter must be smaller than the bore; use the measured or offset diameter if it is worn.
What this means: Specified peripheral feed
- What it is
- The feed you want at the cutting edge where it meets the wall, worked out from your chosen feed per tooth, teeth and spindle speed.
- Units and format
- Enter a number in mm/min: millimetres per minute. The form accepts 0.001 mm/min to 1000000 mm/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1000 mm/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Tool-centre feed is directly proportional to the peripheral feed.
- Get it right
- Many controllers program the tool centre, so do not apply this correction twice if CAM or the control already does.
Method and formulas
- Centre-path diameter = work diameter − cutter diameter internally, or work diameter + cutter diameter externally.
- Centre feed = peripheral feed × centre-path diameter/work diameter. Full-circle time = π × centre-path diameter/centre feed.
- Example: a 10 mm cutter inside a 50 mm bore at 1000 mm/min peripheral feed needs 800 mm/min centre feed. One 40 mm centre-path circle takes 0.157080 min.
Limitations
- Constant-height 2D motion at constant speed only; helical motion, acceleration and entry are excluded.
- CAM/controller compensation conventions vary. Applying the correction twice gives the wrong feed.
- This tool does not select radial engagement or an acceptable cutting load.
- Default values are worked examples, not recommended settings or material properties.
Typical uses
- circular milling
- internal interpolation
- tool centre feed
Who it is for
- CNC programmers
- Machinists
What you get
- Centre-path diameter
- Tool-centre feed
- Full-circle travel and time
Interpreting the result
- Confirm whether the controller expects centre or compensated contour feed.
- Review the path using the established setup procedure.
References
- Sandvik Coromant: Milling formulas and definitions — https://www.sandvik.coromant.com/en-gb/knowledge/machining-formulas-definitions/milling-formulas-definitions
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