Engineering Resource

The main cost drivers

• Material: cost, availability and how difficult it is to cut.
• Machine time: driven by material removal volume, tool life and cutting parameters.
• Set-ups: each one adds time, fixturing and stack-up error.
• Tolerance and finish: tighter values demand extra passes, temperature control and measurement.
• Inspection and documentation: CMM time, reports and certificates are real work.
• Batch size: set-up and programming cost is amortised across the quantity.

Why tolerance and finish step up, not slope

Cost does not rise smoothly as a tolerance tightens; it steps. Crossing from a general tolerance to a tight one may add a semi-finish pass, in-process measurement and a slower cycle. Crossing again to a temperature-critical tolerance may add a controlled environment and a different class of machine time. Each step is discrete.

How batch size changes the picture

Programming, fixturing and first article inspection are largely fixed costs. Over ten parts they dominate; over thousands they almost vanish. This is why the same part can look expensive as a one-off and economical in series — and why it pays to think about the eventual volume before quoting a prototype.

Reducing cost without losing function

• Loosen tolerances that carry no function, and keep the tight ones where they do.
• Design internal radii the tool can reach in one pass.
• Keep wall thickness uniform and pockets shallow where possible.
• Avoid specifying a fine finish across every face.
• Choose the least difficult material that meets the requirement.