How much should a last time buy cover, and when should a discontinued part be remade to print?

How do you know a custom part is heading for a last time buy?

The clear signal is a written discontinuance or last-order notice from the supplier. The earlier signals are a declined quote, a sudden price jump, a request to accept a different material or process, and tooling that needs repair more often.

Obsolescence specialists call the general problem DMSMS, diminishing manufacturing sources and material shortages: losing, or being about to lose, the makers or suppliers of an item or of the material it is made from. SAE STD0016A sets out how an OEM documents its plan for handling it. For a custom metal part the warning signs are rarely a formal notice. Watch for a supplier that no-quotes a repeat order, quotes it only with a long list of exceptions, asks to change the alloy or bar size because a mill has dropped it, asks to move the work to another plant, or tells you a die or fixture needs major repair before the next run. Each of these means the current source may not exist for the remaining life of your product.

Treat the first warning as the start of the clock, not the formal letter. Once the notice is issued you have one order left and no leverage. Before it is issued you can still ask for samples, measurement data, process records and the return of your tooling, and you can still place a trial order with a second source while the original parts remain available as the reference.

Once a notice or a strong warning arrives, work through these steps before you argue about quantity:

1. Get the dates in writing. The last date you can order, the last date the supplier will ship, and whether it will hold a final lot and release it against scheduled deliveries or ship it all at once.
2. List what belongs to you. Tooling, fixtures, special gauges and any samples you paid for. Ask separately about CNC programs, process sheets and inspection plans; these are often the supplier’s own work, so ask what it will release and on what terms.
3. Capture the last good parts. Have retained parts from the most recent accepted lots measured against every drawing callout, keep several as physical references, and collect the material certificates and inspection records for those lots. Some aerospace buyers formalize this as a last article inspection before production moves.
4. Count real demand and stock. Production, service and your own losses, as in the worksheet below, and only stock that has been inspected.
5. Start the second source in parallel. Send the RFQ for a remake while the original supplier is still running, so a bad first article does not leave you without parts.
6. Plan storage and identification. Label the last time buy stock with part number, revision and lot, protect it from corrosion, and decide who may draw from it.

How do you calculate how much a last time buy should cover?

Add remaining production demand to the chosen end date, service and spares demand, your own yield loss and a margin for forecast error, then subtract stock you already hold or have on order. The end date is either the end of product support or, for a bridge buy, the date a new source will be qualified.

Start by choosing the end date, because it drives everything else. Obsolescence researchers at the University of Maryland define a lifetime buy (also called a life-of-type buy) as one sized to meet current and expected future demand, and a bridge buy as one sized only to reach the next redesign (Feng, Singh and Sandborn, 2007). Writing about electronic systems, Sandborn noted that in hindsight programs often would have avoided more cost by bridge-buying parts to a single planned redesign date than by resolving each obsolete part to the end of the system’s field life, while cautioning that this is not the best approach for every system (DSP Journal, 2008). The same reasoning carries over to a single custom part: if you can realistically qualify a new source, buy only to that date.

Then build the quantity from separate lines rather than one guess. Production demand comes from the build plan to the end date. Service demand comes from the installed base and the observed replacement rate, which your field returns or spare-parts sales history will show better than any forecast. Add the parts your own process consumes, such as assembly scrap, test failures and parts pulled for audits. Finally add a margin for uncertainty, which grows with the length of the period you are covering.

The margin is a cost trade, not a matter of taste. The same Maryland work breaks the cost of a lifetime buy into procurement, inventory, disposal and penalty (shortage) costs. Every part you buy and never use costs its price plus years of storage and tied-up capital, and may end as scrap. Every part you are short costs whatever a line stop, an emergency redesign or a lost service contract costs. Standard inventory theory for one-time buys (the newsvendor model) sets the target probability of not running short at the shortage cost divided by the sum of the shortage cost and the excess cost, so a part whose shortage would stop a product line justifies a much larger margin than a cosmetic bracket. Two practical checks keep the result honest: confirm the supplier can actually make the quantity before the window closes, and check how the parts will survive storage. Unprotected carbon steel rusts and some coatings age, so specify packaging, preservation and periodic inspection for the stock as part of the buy.

What do you need before a discontinued part can be remade to print?

A drawing and model that fully define the part, the right to use them, the material and finish specifications, a set of good reference parts with their measurements, and either the original tooling or a plan and budget for new tooling.

Check the drawing against reality before the old supplier is gone. Drawing practice under ASME Y14.100, with dimensioning and tolerancing per ASME Y14.5, expects the drawing to define every feature completely enough that another shop could make the part from it. In practice, long-running parts drift away from their prints. The old supplier may have added a chamfer to stop a burr, adjusted a casting to fill better, used a specific plating thickness that the drawing leaves open, or worked under a deviation that never became a revision. Pull retained samples from recent good lots, measure them against every callout, and record where the parts and the drawing disagree. Ask the supplier for its process records, inspection data, material certificates and any approved deviations while it still has a reason to cooperate.

Where the drawing is missing or unusable, reverse engineering from samples can recover the geometry, and a material analysis and hardness check can recover the alloy and condition. What measurement cannot recover is the tolerance the function needs, so an engineer has to set it from the mating parts and the use, not from the spread of a few samples. Treat the result as a new drawing at a new revision.

Plan for qualification. In aerospace, AS9102 calls for a full first article inspection, or a partial one covering the affected characteristics, when the manufacturing source, location of manufacture, process, tooling or material changes in a way that can affect fit, form or function. Moving a discontinued part to a new supplier is exactly that kind of change, and the same discipline works in any industry. Ask for a ballooned first article report against the current revision, compare it with your reference samples, and test-fit the parts in the assembly before you let the last time buy stock run down. The first article inspection guide lists what that report should contain.

How is a remake-to-print of a discontinued part handled on a Saola order?

Send the drawing, the model, reference samples or their measurement data, and the quantity you need to bridge or to cover the remaining life. The quote states which plant would make each operation and the country of origin, and comes with a manufacturability note that flags callouts that are unclear or that your sample data contradicts.

Saola Manufacturing is the brand of Aximora Global Trading Co., Ltd., a Ho Chi Minh City company that places and manages metal-parts work; it is not itself a factory. Machined parts are made by CNC turning and CNC milling at our lead CNC plant, T.K Viet Nam Precision Company Limited. Die casting, sand casting, stamping and all surface finishing go to partner plants we manage, which are not named and are not necessarily in Vietnam. Each quote names the production site and the country of origin, so a remade part is never presented as Vietnamese origin unless it is made there.

For a part whose original tooling is being transferred, tell us who owns the tool and send its drawings or photos, so the receiving plant can say whether it can run the tool as it is. For a machined part remade from samples, expect questions about tolerances that the samples cannot answer. ISO 9001 certification is in progress, not held. To start, send the package through the quote form.