One Supplier or Five? The Hidden Cost of Splitting a Drawing
One Supplier or Five? The Hidden Cost of Splitting a Drawing
A housing needs milling, turning, heat treatment, and black anodizing. The straightforward way to buy it: find a milling shop, a turning shop, a heat treater, and an anodizer, and manage four purchase orders. Each supplier is a specialist, each quote is individually competitive, and the total looks good on a spreadsheet.
Then the parts arrive, the assembly does not fit, and four companies explain why it is not their problem. This article is about the costs that never appear on those four quotes.
The Visible Math vs the Real Math
Split sourcing wins the visible math: each specialist quotes aggressively for its own process, and nobody carries a coordination margin. What the spreadsheet misses:
– Coordination hours. Every PO is created, acknowledged, expedited, and received separately. Every drawing question is asked four times, answered in four formats, and reconciled by hand. – Freight fragmentation. Four suppliers shipping separately means four sets of freight, customs entries, and packaging — often more than the savings the split was meant to capture. – Queue stacking. The part’s lead time is not the sum of process times; it is the sum of each shop’s queue, plus transit between them, plus the days your own team spends chasing status between steps.
For a part with three or more outsourced processes, these invisible lines routinely exceed the unit-price advantage of the cheapest specialist.
The Technical Cost: Nobody Owns the Interfaces
Split production has a deeper problem than administration: the datum chain breaks at every handoff.
The milling shop machines datum faces. The turning shop — working from a different fixture, in a different shop, weeks later — must hold features to those same datums without knowing what the milling shop actually achieved. Each transfer adds its own small deviation, and no one measures the accumulated result because no one sees the whole part.
When the assembly fails at your incoming inspection, each supplier is individually correct: their process, their report, their tolerance, all in order. The failure lives in the seams between them, and the seams belong to you.
The Accountability Question Worth Asking
Before splitting a drawing across shops, answer this: if the part fails at assembly, who reworks it, and how fast?
Under split sourcing, the honest answer is: whichever supplier can be argued into it, on whatever timeline their queue allows — while your team does the forensics. Under single-point production, one party measured the finished part against one drawing revision and put their name on the report. The rework conversation is one phone call, not a summit.
When Splitting Actually Makes Sense
To be fair, there are cases where splitting is the right call:
– The part needs one process only — no chain, no handoffs, no seams. – You have genuine volume, where in-house-equivalent pricing from a specialist outweighs all coordination cost. – The processes are genuinely independent: no shared datums, no fit relationships, commodity-grade tolerances.
If none of these apply, the split is buying you risk, not savings.
A Middle Path: Coordinated Production
There is a third option between “one factory does everything” and “you manage five vendors”: a supplier that owns the drawing revision, schedules and releases production across vetted specialist shops, and inspects the finished part against the original datums before shipment.
The test for whether a supplier can genuinely do this is simple: ask who inspects the completed part against the full drawing, and who is accountable if the assembly does not fit. A coordinated producer answers with a name and a report. A broker answers with reassurance.
One drawing revision, one schedule, one inspection standard, one party accountable — that is the actual product. The machining is procurement.