The decision to buy a polishing line is usually framed as a cost question, and it is really four questions: cost, lead time, quality control and risk. Suppliers of machines tend to answer only the first one, and they tend to answer it optimistically. This page tries to answer all four, including the cases where outsourcing is the better answer.
When outsourcing genuinely wins
- Volume is low or irregular. A line has a fixed cost that does not care whether it runs. If your finishing requirement is 3,000 square metres one month and 800 the next, the cost per square metre in-house will swing wildly while the outsourced rate stays flat.
- The finish mix changes constantly. Every finish change costs setup time and consumables. A subcontractor who runs that mix all day absorbs the changeover; you would absorb it on every order.
- You have no finishing expertise yet. A polishing line is not self-operating. The first months involve learning pressure, speed, abrasive sequence and inspection — and that learning curve produces scrap. Paying someone else to have already learned it is a legitimate strategy.
- Capital is constrained. A line ties up capital and floor space for a decade. If the same capital can earn more elsewhere in the business, outsourcing is the better allocation.
When in-house wins
- Volume is high and stable. The fixed cost of the line gets spread over enough square metres that the variable cost dominates, and the variable cost in-house is usually well below an external rate.
- Lead time is a competitive weapon. External finishing typically adds days or weeks. In-house can turn a finishing step into hours, which changes what you can promise customers.
- Quality tolerance is tight and cosmetic. You cannot adjust a subcontractor's head pressure. If a batch is marginal, in-house lets you re-run it; outsourced means a negotiation.
- You are developing new surfaces. Product development needs iteration speed that a subcontractor's schedule rarely allows.
- Supply risk matters. One external supplier is one point of failure, and your orders are not its priority when its capacity is tight.
The costs outsourcing hides
The external rate per square metre is visible, which makes it feel like the full cost. It is not. Add freight both ways, packaging for transit, incoming inspection, the labour to handle receipts, scrap caused by damage in transit, and the working capital tied up in material that is off-site for two weeks. On cosmetic stainless, transit damage alone can be a meaningful percentage.
There is also the cost of the constraint itself: if the subcontractor is busy, your lead time extends and you may lose orders you never see in the accounts.
The costs in-house hides
The machine price is the visible part. Less visible: floor space, foundation and power connection, extraction ducting, the operator you have to hire or reassign, the supervisor who has to learn a new process, spare parts inventory, abrasive inventory, and the scrap generated while the process is being dialled in.
Then there is the cost of under-utilisation. A line running at 40 percent of capacity still consumes depreciation, space and maintenance at 100 percent. That is the single most common reason an in-house decision that looked good on paper underperforms in practice.
Quality control is the argument people underrate
Cost comparisons tend to assume both options deliver the same quality. They usually do not, in both directions. A good subcontractor with a dedicated line and years of experience will outperform a new in-house line for the first year. An in-house line with a committed operator will eventually outperform a subcontractor who is juggling five customers.
What matters is whether you can specify, measure and enforce the finish. If you cannot measure it, you cannot manage it in either direction, and the cheapest option will win by default.
A decision checklist
- Annual volume, and the month-to-month variation
- Number of finish changes per week
- External rate per square metre, including freight and damage
- In-house variable cost per square metre, with consumable data from the supplier
- Installed capital cost, not machine price
- Realistic utilisation based on committed orders
- Lead time advantage, and its value to your customers
- Whether you can measure the finish you are specifying
- Whether you have, or can hire, someone to own the process
If more than two of those answers are unknown, the decision is being made on price alone — and price alone is the weakest basis for a ten-year capital decision.
A middle path that is often overlooked
Many shops start with a single-finish line for the highest-volume product and continue to outsource the rest. That captures most of the variable cost saving without taking on the full complexity of a universal line, and it keeps the learning curve contained. It also leaves the outsourcing relationship intact as a backup for peak demand, which is worth more than it costs.