Tool-life cost allocation

Purpose and cost boundary

Specify the insert or solid tool, usable index positions, cutting life, change time and life endpoint. Sandvik Coromant’s April 25, 2024 Productivity Analyzer turning tutorial records these separately. Sandvik turning-test tutorial

In the example, five inserts with four positions each give four complete sets of active edges because the inserts are indexed together. At 30 cutting minutes per set and 0.5 minute per part, $60 of inserts covers 240 processed parts. Add $12 for indexing and divide by 228 accepted parts to get about $0.316 per accepted part. If the cycle-time charge already covers indexing, omit the separate time charge.

Define whether the reported result includes consumables only or also labor and machine time. Keep an estimated quotation allowance separate from observed consumption. Record the tool/insert designation, workpiece material and condition, operation, cutting data, coolant strategy, life endpoint, and output quality requirement so the estimate has a reproducible basis.

Life must have a unit and endpoint

Tool life may be recorded as cutting minutes, completed features, parts, or another explicitly defined measure. NIKKEN's tool-life calculator asks separately for anticipated tool life in minutes, tool time in cut per cycle/feature, and the number of similar cycles/features. This distinguishes exposure that consumes the edge from total elapsed shift or cycle time. Loading, probing, traversing, and waiting still consume production capacity, but should not automatically be treated as minutes of cutting life. NIKKEN tool-life calculator inputs

For a constant operation with no quality losses:

Parts per edge = usable cutting life per edge / cutting time per part
Edge cost = insert price / usable indexed edges per insert
Consumable cost per part = edge cost / parts per edge

All times must use the same units. If a part has several identical features, include all their cutting time. Round operational replacement quantities to feasible complete parts or features where an edge cannot safely finish the next one; retain unrounded values only as a clearly labeled long-run estimate.

The endpoint also matters. Sandvik's tutorial records a tool-change criterion, not merely a time. Do not present a catalog starting condition or the longest observed run as a guaranteed production life. Sandvik test setup and change criterion

Count usable edges and insert positions correctly

Separate the number of inserts operating in a cutter from the number of indexable positions on each insert. Four positions on each of five inserts are four complete cutter sets, not twenty times the life of a fully loaded cutter. Sandvik's tutorial separately enters the insert quantity and number of edges, illustrating why both are needed. Sandvik insert inputs

Original illustrative example, not manufacturer pricing or life data: a five-insert cutter uses inserts costing $12 each. Each insert yields four usable index positions; all five are indexed together. A set of active edges lasts 30 minutes in cut, and each part requires 0.5 cutting minute.

This assumes equal edge life, no broken inserts, and full use of all four sets. Actual replacement of individual inserts requires an appropriate consumption record rather than an assumed synchronized set.

Changeovers and good-output reconciliation

Continue the original example: assign four two-minute indexing/replacement events over the complete 240-part life cycle. At an illustrative combined machine-and-labor charge of $90/hour, eight minutes cost $12. This convention charges one event per set consumed over repeated production; a finite job must instead use its actual event boundary, including any separately charged initial setup.

Insert consumption                         $60
Allocated indexing/replacement time         $12
Total defined tool-related cost             $72
Processed parts                             240
Accepted parts                              228
Cost per accepted part = $72 / 228      $0.315789...

At 100% acceptance the same pool would be $0.30/part. Dividing by 240 while labeling the result “per good part” would conceal the 12 rejected parts. This pool excludes their material and other processing costs; report those elsewhere rather than pretending the tooling allocation covers the complete scrap loss.

Do not add the eight minutes again if the machine cycle-time charge already includes these same events. Likewise, do not add a second operator rate when the $90/hour combined rate already includes it. Automatic tool changes within a normal part cycle and manual edge indexing after wear are different events; identify which your time model includes.

Reconditioning and total productive life

Seco's current service page limits reconditioning to eligible Seco solid-carbide tools, including selected drills, end mills, and reamers. It describes inspection, regrinding, recoating, and quality control, and warns that excessive wear or damage can prevent restoration. Reconditioning is therefore a conditional additional life, not an automatic multiplier applied to every tool. Seco reconditioning service

Separate original illustration: a solid tool costs $120 new; two accepted reconditioning services cost $40 each. Suppose observed cutting lives are 100, 90, and 80 minutes. Total defined tool expenditure is $200 and total cutting life is 270 minutes, giving $200 / 270 = $0.740740… per cutting minute. At 0.5 cutting minute per part and full acceptance, that is $0.370370… per part, excluding handling, freight, changes, and inspections. Charging $120 anew for each restored life would overstate the defined purchase expenditure.

Seco's December 2022 service announcement discusses typical repeat reconditioning and indicative savings. Those historical program claims are not the inputs to the example above or a guarantee for a specific tool. Confirm eligibility, restored dimensions, price, lead time, and the life actually achieved in the application. Seco December 2022 announcement

Compare complete process results

Life changes with the application. Sandvik's milling guidance explains that cyclic heating and cooling can produce thermal cracking and premature edge failure; its dry-versus-fluid discussion is process-specific, not permission to change coolant solely to improve a cost spreadsheet. Re-establish the qualified cutting conditions when comparing trials. Sandvik dry milling or cutting fluid

Compare tool consumption, changes, elapsed time and rejects against accepted output. Retain the sample size, distinguish planned indexing from breakage, and account separately for reusable tooling that spans jobs.

Related reference

Cost structure and cost bases