In manufacturing, a quote is only as reliable as its bill of materials: thousands of part numbers nested in assemblies, made or bought, bought in lots, shared across products. This is how I went from that problem to an interface to create, assemble, view and approve a BOM, with its costs always in sight.
Every quote for a manufactured product rests on its bill of materials. Before this project, BOMs and their costs lived in a very complex Excel workbook, managed through many versions, each with a huge number of columns.
With several copies in circulation it was hard to know which one was current, and a flat sheet made a tree-shaped structure hard to read. The goal was to simplify: one structure, one place, costs always in sight.
And the structure itself is unforgiving. When a single price, quantity or part changes, the cost moves through branches that look unrelated.
The work didn’t start from screens. It started from the client’s process as it really ran in their spreadsheets. We analysed it in depth: what worked and had to be kept, where it broke, and how its elements depended on each other. Only then did we give each aspect of configuring a BOM its own place in the interface.
A bill of materials is the recipe of a product: every assembly and part needed to build it, each with a part number, a quantity and a cost. The cost of the product is the sum of its parts, rolled up level by level.
A real BOM isn’t three levels and six parts. These are the forces that make it hard to read and harder to price.
Every item has its own PN. There are thousands of them, and a wrong or duplicated code breaks everything downstream.
Each item is either produced in-house, with a cost built from its own structure, or bought, with a cost set by suppliers.
Unit costs change with the lot: supplier price breaks on one side, setup costs spread over the batch on the other.
Assemblies inside assemblies, and every level multiplies the quantities below it.
The same PN appears in many assemblies, so one change lands in many places.
A BOM drives prices and production. It has to be checked and approved before anyone relies on it.
Every item in a BOM carries one decision that changes everything about it: is it made or bought? A make item is produced in-house, so it has its own structure and its cost is built from it. A buy item is purchased, so the structure ends there and its cost comes from a supplier.
The interface has to make this difference visible at a glance, because the same question, “why does this cost what it costs?”, has two completely different answers.
In the interface, make or buy isn’t a tag typed on each line. It can be configured by type and by characteristics, and each side loads its costs from its own source: cost centres for what is made, quotes, orders and offers for what is bought.
The decision also depends on quantity. The cheaper option can flip as the lot grows.
| Lot size | Buy · unit price | Make · unit cost | Cheaper |
|---|---|---|---|
| 100 | €0.12 | €0.46 | Buy |
| 1,000 | €0.09 | €0.10 | Buy |
| 5,000 | €0.09 | €0.068 | Make |
The most difficult point in the analysis was cost centres. Costing a make item means knowing what each hour of in-house work costs, and the client needed to follow every single cost over seven years: averages, and a projection for each year ahead.
In Excel this was done by hand. We gave cost centres a dedicated tool of their own, then connected it to BOM costing. Two people, two tools, one source of truth: cost control manages centres, averages and the 7-year projection; whoever costs a BOM selects a make part number, picks its cost centre, and the right value arrives on its own, based on the costing date.
Instead of one screen that tries to do everything, I organised the interface around the life of a BOM: from the first part number to the approved structure that prices and production rely on. Each stage gets the view it needs.
Each decision answers a weak point found in the analysis.
A built-in approval step, with clear states
A BOM is checked before it drives a price.
Total cost per part number, rolled up at every level
The full cost of any PN, and what makes it up, is always visible.
A structure view: where each PN lives, how it’s organised, what depends on it
The impact of a change is visible before it’s made.
Make or buy configurable by type and by characteristics
Rules replace line-by-line decisions, and stay consistent.
Connected databases: cost centres for make; quotes, orders and offers for buy
Costs come from their source, not from a copy.
A dedicated cost-centre tool with averages and 7-year projections, recalled by BOM costing
Each role works in its own tool, and the right rate arrives automatically for the costing date.