BIZOMAT MAKEOS · Manufacturing
Milling Time and Cost per Part with Tool Life
How long does this milling operation take and what does it cost per part, including tool wear and set-up?
Cost of a milling operation per part: cutting time from the volume to remove and the removal rate (from width, depth and table feed), tool edges used from the tool life at those conditions, tool change time and edge cost, non-cutting time, set-up spread over the batch, and the machine rate, with the cost breakdown.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Volume to remove | cm³ | Volume of metal removed per part. |
| Radial width of cut | mm | Radial width of cut. |
| Axial depth of cut | mm | Axial depth of cut. |
| Table feed | mm/min | Table feed (from a milling cut plan). |
| Tool life at these conditions | min | Tool life in cutting minutes at these speeds and feeds (from tests or the tool maker). |
| Inserts (edges) per change | Number of inserts replaced at each tool change. | |
| Cost per edge | $ | Cost of one cutting edge. |
| Time to change all edges | min | Time to index or change all the edges. |
| Non-cutting time per part | min | Rapids, approach, probing and tool changes per part. |
| Machine and labour rate | $/h | Machine plus operator rate. |
| Set-up time per batch | min | Set-up time for the batch. |
| Batch quantity | Parts per batch. |
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: Volume to remove
- What it is
- The volume of metal machined away from one part in this operation: the difference between the blank and the finished shape.
- Units and format
- Enter a number in cm³: cubic centimetres. The form accepts 0.000001 cm³ to 10000000 cm³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 120 cm³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Cutting time and tool use rise in direct proportion.
- Get it right
- CAD can give it as blank volume minus part volume; check it is cm³, not mm³.
What this means: Radial width of cut
- What it is
- How much of the cutter’s width is engaged in the material, measured sideways across the feed direction.
- 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 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Removal rate is proportional to it, so cutting time falls as it rises.
- Get it right
- Use the average engagement along the tool path; for a full slot it equals the cutter diameter.
What this means: Axial depth of cut
- What it is
- How deep the cutter cuts along its own axis in each pass.
- 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 8 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Removal rate is proportional to it, so cutting time falls as it rises.
- Get it right
- Use the depth per pass, not the total depth of the feature if it takes several passes.
What this means: Table feed
- What it is
- The speed at which the table or cutter travels along the tool path while cutting.
- Units and format
- Enter a number in mm/min: millimetres per minute. The form accepts 0.000001 mm/min to 100000 mm/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 573 mm/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Removal rate is proportional to it, so cutting time falls as it rises.
- Get it right
- This is the table feed per minute, not feed per tooth or per revolution; multiply those by teeth and spindle speed first.
What this means: Tool life at these conditions
- What it is
- How many minutes of actual cutting one set of edges lasts at these speeds and feeds before it must be indexed or changed.
- Units and format
- Enter a number in min: minutes. The form accepts 0.000001 min to 100000 min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 45 min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Shorter tool life means more changes per part, raising tool change and insert costs.
- Get it right
- Count time in the cut only, not clock time on the machine, and use a value that matches these cutting conditions.
What this means: Inserts (edges) per change
- What it is
- How many cutting edges are replaced each time the tool is changed or indexed, normally one per insert pocket on the cutter.
- 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 4 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Insert cost per part is directly proportional to it.
- Get it right
- Count edges indexed at each change, not the number of edges each insert has.
What this means: Cost per edge
- What it is
- The cost of one usable cutting edge: the insert price divided by the number of edges it offers.
- Units and format
- Enter a number in $: an amount of money; use one currency for every money input. The form accepts $0 to $10000. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $3 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Insert cost per part is directly proportional to it.
- Get it right
- Divide the insert price by its usable edges; entering the full insert price overstates tooling cost.
What this means: Time to change all edges
- What it is
- The machine time lost each time all the edges on the cutter are indexed or replaced.
- Units and format
- Enter a number in min: minutes. The form accepts 0 min to 600 min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Tool change time cost rises in proportion.
- Get it right
- Enter minutes, not seconds.
What this means: Non-cutting time per part
- What it is
- Time each part spends on the machine without cutting: rapids, approach moves, probing and tool changes.
- Units and format
- Enter a number in min: minutes. The form accepts 0 min to 600 min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.5 min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Adds machine time cost per part at the machine rate.
- Get it right
- Enter minutes per part, and include part loading only if the machine waits during it.
What this means: Machine and labour rate
- What it is
- The cost of one hour of the machine together with its operator, including overheads, from your costing.
- Units and format
- Enter a number in $/h: money per hour. The form accepts $0/h to $10000/h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $110/h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- All time-based costs rise in proportion.
- Get it right
- Use the combined machine and labour rate, not the operator’s wage alone.
What this means: Set-up time per batch
- What it is
- The time to set up the machine for the batch: fixturing, loading programs, touching off tools and first-off checks.
- Units and format
- Enter a number in min: minutes. The form accepts 0 min to 100000 min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The set-up share per part is this time at the machine rate divided by the batch.
- Get it right
- Enter the time for the whole batch in minutes, not per part.
What this means: Batch quantity
- What it is
- How many parts are made from one set-up, over which the set-up cost is shared.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 100000000. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The set-up share per part falls in inverse proportion to batch size.
- Get it right
- Use the quantity actually run per set-up, not the yearly volume.
Method and formulas
- Removal rate Q = a_e a_p v_f; cutting time = volume ÷ Q.
- Tool changes per part = cutting time ÷ tool life.
- Cost = rate × (cutting + non-cutting + changes × change time + set-up ÷ batch) + changes × edges × edge cost.
- Example: removing 120 cm³ takes 2.6178 min of cutting; the part costs about 10.767.
Limitations
- Single operation at constant conditions; finishing passes need their own line.
- Tool life must match the speeds and feeds used.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Quote a milled part
- Compare a faster cut that wears tools quicker
- See what share of cost is tooling, cutting and set-up
Who it is for
- Estimators
- Manufacturing engineers
- Production managers
What you get
- Removal rate and cutting time
- Tool changes per part
- Cost per part breakdown
Interpreting the result
- When set-up dominates, bigger batches pay; when tooling dominates, slower speeds may be cheaper.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1084–1101, 1146–1152. Topic reference; no source tables or recommended settings are reproduced.
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