Cost per Part Calculation
October 18, 2026 · 铸屹精密
Why Cost per Part Beats Tool Price
Machine shop buyers and process engineers rarely fail because they bought the wrong catalog number. They fail because they compared the wrong number. A $9 end mill that lasts 40 parts is more expensive than a $22 end mill that lasts 300. Cost per part (CPP) puts every quote on the same footing, and it is the single fastest way to justify a tool change to a purchasing manager who only sees invoice lines.
The Formula and Two Worked Examples
The working formula is simple, but each input must be measured rather than guessed:
Cost per part = Tool price ÷ (Regrind life × Number of regrinds + 1) × Parts per edge life
A practical shorthand many shops use is to divide tool price by total parts produced across the full tool cycle, including regrinds. Below, the same math applied to two materials.
Example 1 — Aluminum (non-ferrous, high-gloss finishing). For mirror-finish aluminum work, PCD or DLC-coated carbide is the usual choice because PCD delivers the highest hardness and DLC offers the lowest friction coefficient, preventing built-up edge. Assume a PCD-tipped face mill at $120, producing 900 parts per life cycle, with three regrind cycles available. Total parts across the cycle: 3,600. CPP = $120 ÷ 3,600 ≈ $0.033 per part. A cheaper uncoated carbide tool at $30 that yields 250 parts and two regrinds gives 750 parts, or $0.040 per part — 21% more, despite looking cheaper on the PO.
Example 2 — Hardened steel (HRC 55+ finishing). Here CBN or AlTiN-coated carbide is appropriate; AlTiN offers the best heat resistance for high-speed dry cutting and hardened steel. Take a $95 AlTiN-coated ball nose with 180 parts per life and four regrinds: 900 total parts, CPP ≈ $0.106. Compare an imported premium grade at $240 with 220 parts per life and four regrinds: 1,100 parts, CPP ≈ $0.218. The domestic route wins on cost per part by roughly half, while imported premium grades remain worth selecting only where tolerances are extreme.
How to Collect Life Data You Can Trust
CPP collapses if the life numbers are marketing claims. Collect them yourself, within one machine and one setup:
- Log tool ID and batch number, then record parts completed at each edge change over at least three cycles.
- Track regrind count and post-regrind performance separately; a reground tool should be re-measured and re-coated, with inspection data retained.
- Note failure mode (flank wear, chipping, built-up edge) — an unstable process produces meaningless averages.
For shops without the bandwidth, this is where a supplier's process support matters. 铸屹精密（Exactalloy）controls出厂跳动 within 0.005mm, supplies batch-traceable tools, and offers regrind-and-recoat service that typically cuts tool purchase cost by 30–50% while shortening lead time versus 8–12 week import cycles. Their application engineers also help match substrate and coating to the material — PCD for non-ferrous gloss work, CBN for hard steel finishing, AlCrN for stainless and superalloys, TiCN for drilling and tapping — and can confirm whether a generic carbide grade covers your case or an imported premium grade is genuinely required.
Next Step
Pick your two highest-consumption tools this month. Record tool price, parts per life, and regrind count for each, then compute CPP side by side. If the gap exceeds 20%, request a trial sample and a regrind quote before your next PO — that single comparison usually pays for the switch.