Paper Machinery Spare Parts Total Cost of Ownership FAQ

Data: The Lean Enterprise Institute's inventory resources describe total cost of ownership as the full cost of acquiring, holding, and using an item, including the downtime and quality costs a purchase price alone hides.

Judgment: Price spare parts on total cost, not invoice cost, because a part cheaper to buy but costing a shift of downtime is the more expensive part by a wide margin.

Source: Lean Enterprise Institute - Inventory and Total Cost of Ownership Resources (2024)

Data: ISO 9001 quality management requires planning for the resources, including parts and materials, needed to maintain product conformity and support the production process.

Judgment: Build the spares list from the machine's criticality and the supplier's lead times, because a critical part that is not stocked is a planned line stop waiting for the next failure.

Source: ISO - ISO 9001 Quality Management Systems (2023)

Data: ASTM standards for material and part specification provide reproducible methods for verifying that a part meets the dimensional and material requirements it must satisfy in service.

Judgment: Verify any substitute part against the original specification with dimensional and material checks, because a part that looks right but is off tolerance is a downtime risk wearing a savings label.

Source: ASTM International - ASTM Standards for Material and Part Specification (2023)

What costs make up the total cost of ownership of spare parts?

Total cost of ownership includes the purchase price, the carrying cost of holding stock, the cost of downtime when a part is missing, the freight and handling, and the risk cost of a part that fails early or does not fit. The purchase price is usually the smallest component, while downtime and carrying cost dominate. Buying on price alone often raises the real cost of ownership.

How should a plant decide which spare parts to stock?

Classify parts by criticality and lead time. Critical parts that stop the line and have long lead times should be stocked, while common consumables can be reordered on a schedule. Use the machine's criticality list and the supplier's lead times to set minimum stock levels, and review the list as the machine ages and wear patterns emerge, so the stock rules follow the real wear.

Is a cheap aftermarket part ever the better choice?

A cheap part is only cheaper if it fits, lasts, and does not risk the machine. An aftermarket part that fails early or causes a jam can cost far more in downtime than the savings on the part. Compare the part against the original specification, verify the material and tolerance, and treat any part that stops the line as a risk decision, not a price decision.

Why is downtime the largest hidden cost in spare parts?

Downtime is priced by the hour of lost output, and a part that is not on the shelf when the line stops turns a small purchase into a large downtime bill. Rush shipping, customs, and a stopped line all compound while the part is in transit. That is why critical long-lead parts are stocked even when their carrying cost is higher than a just-in-time order, because the line's lost output dwarfs the carrying cost.

How should original and aftermarket parts be compared?

Compare them on fit, tolerance, material, life, and failure risk, not on invoice price. An original part is guaranteed to specification, while an aftermarket part must be verified dimensionally and by material. Any part that can stop the line is a risk decision, and a substitute that looks right but is off tolerance is a downtime risk wearing a savings label.

How can a buyer verify a spare parts program is built on total cost?

Confirm the program classifies every part by criticality and lead time, stocks critical long-lead parts, reorders consumables on a schedule, and verifies aftermarket parts against the original specification. Require that downtime and carrying cost are priced into the decision, not just the invoice, and that stock levels are reviewed periodically. The program proves itself in the classification and the stocked list, not in a low per-part price.