Guide
How to Estimate Machining Time
Estimate quote-stage job time from setup, measured cycle time, good-part quantity, scrap allowance, inspection, and shop-specific efficiency before moving the case into the calculator.
Direct answer: total job time = setup time + (cycle time x good quantity) + scrap allowance + inspection and queue allowances.
Page role: quote-stage total job time estimation using setup time, cycle time, good quantity, scrap allowance, and measured efficiency. Use this page before quoting, then use the calculator to repeat the model consistently.
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Total Job Time = Setup Time + (Cycle Time x Good Parts) + Allowances
Estimating a job isn't just about how long the tool is in the cut. It's about the entire door-open-to-door-open process.
1. Setup Time (Fixed)
- Cleaning machine / Vise alignment
- Tool setting / Touch off
- First Article Inspection (FAI)
- Program proofing
2. Cycle Time (Variable)
- Cut Time: Tool actually removing metal
- Non-Cut Time: Rapid moves, Tool changes
- Load/Unload: Operator interaction
The 3-Step Estimation Process
Calculate "Time in Cut"
Determine the length of the tool path and divide by the feed rate.
Add Non-Cutting Time
The "Hidden" costs. Machines aren't cutting 100% of the time.
- Tool Changes: Allow 5-10 seconds per tool.
- Rapid Moves: Add 10-20% to your cut time for air cutting.
- Spindle Ramping: 3-5 seconds to reach RPM.
Apply Measured Efficiency
Estimate with the efficiency actually measured on the relevant machine, fixture family, and operator workflow.
Measured efficiency rule:
Use measured efficiency by machine family; do not treat 80% as a universal constant.
Real World Example: Aluminum Plate
Job: Face mill a 10" x 6" Aluminum plate.
Tool: 3" Face Mill, 5 Flutes.
| Parameter | Value |
|---|---|
| Cut Speed (IPM) | 150 IPM |
| Total Travel Length | 14 inches |
| Base Cut Time | 0.09 min |
| Non-Cut Time (Load/Unload/Rapids) | + 1.50 min |
| Total Estimated time | ~1.6 min |
Related Guides
Audit the base formula in how to calculate CNC machining time before converting the estimate into quote-stage job time, then use machining time reduction after the baseline is measured.