---
title: "Buy the housing finished, or buy it rough and machine it in-house?"
url: https://partimation.com/for/procurement/make-vs-buy/
description: "Splitting the scope with a supplier is usually argued, not costed. Partimation builds the whole route and prices every step in-house or at your own accepted vendor's markup, with the queue days it adds — and stops short of shopping that step around your supply base, because nothing here does that."
---

# Buy the housing finished, or buy it rough and machine it in-house?

Splitting the scope with a supplier is usually argued, not costed. Partimation builds the whole route and prices every step in-house or at your own accepted vendor's markup, with the queue days it adds — and stops short of shopping that step around your supply base, because nothing here does that.

## A concrete case

A cast-and-machined pump housing, 300 a year, has been bought finished from one supplier since the program started. Your own plant now has CNC capacity it is not using, heat treatment and hard-chrome plating already go outside on other part numbers, and the plant manager wants to know whether buying the rough casting and finishing it internally is worth doing. The supplier has quoted a single delivered figure, so the finishing operations inside it have no price of their own that anyone can point at. What is on the table is a scope decision — which operations sit in the purchase order and which sit in your own plant — and the only inputs you have are a released STEP file and last year's price.

## How it plays out

1. **Build the whole route before you decide where to cut it** — One upload returns the actual manufacturing route as route cards, one per step: tooling, forming, degating and fettling, heat treatment, machining, finishing, and the handling and queue time each move between departments actually costs. Every card names the process, the department and the rule that put that step there. Before this exists you are arguing about a boundary in a process nobody has written down; after it, the boundary is a line you can point at on a route.
2. **Read the in-house or sourced mark on every step** — Each step is marked as running in-house or priced with your own accepted vendor's markup, with the markup percentage and the queue days that step adds shown against it. The plating and heat-treat steps carry their cost and their days in the same place as the machining steps, so the version where your plant does the finishing and the version where the supplier does it differ by figures rather than by whose turn it was to be confident.
3. **Check that your own plant can really hold the features** — Holes, pockets, flats, bores and bosses are detected off the model, each with a confidence, and a real voxel removal simulation against actual tooling shows exactly what stock cannot be reached. Spare capacity is not the same as capability, and a bore your machines cannot get to is the part of an in-house case that usually surfaces after the scope has already moved. Collision and fixture modelling are deliberately not part of this, so treat it as a reach check, not a machine-safety check.
4. **Rank the two scopes on one ledger** — Candidate routes come back ranked cheapest, quickest and fewest-steps, and every cost line under them traces to a named rate, a posture setting or a rule in the engine. Buying finished usually wins on steps and days; buying rough usually wins on the delivered price and loses some of it back to transfers and queue. Both versions are priced the same way, which is the only reason the comparison is worth anything.
5. **Know where the comparison stops** — Pricing a sourced step uses one accepted vendor's markup. There is no quote solicitation, no marketplace, and no market rate invented on your behalf, so which of your approved suppliers is cheapest for a plating step is not a question the suite answers. What it prices is the work itself and the days it takes, which is the number a supplier's figure then gets held against.

## Where you end up

You end up with two costed versions of the same scope rather than two opinions about it: a delivered route with the finishing inside the supplier's price, and a split route with the rough casting bought and the machining run on your own equipment, each priced line by line and each carrying the queue days its sourced steps add. The decision stops being a plant-capacity argument and becomes a comparison you can put in a sourcing paper. Treat it as decision support and check it against what your plant actually runs before you move a scope boundary that a supply agreement is written around.

## What backs this

- Full manufacturing route builder, ranked — [RouteDFM](https://partimation.com/routing/)
- In-house vs. brokered-vendor step pricing — [RouteDFM](https://partimation.com/routing/)
- Feature-level machining detection + reach simulation — [MachDFM](https://partimation.com/machining/)
- Verified CNC removal simulation — [SimDFM](https://partimation.com/simulation/)
- Itemized cost ledger traced to a named rate or rule — [CostDFM](https://partimation.com/costing/)

## Frequently asked questions

#### Should we buy this part finished, or buy it rough and finish it ourselves?

Two routes, priced the same way, is the honest form of that question. The full route gets built from the model — tooling, forming, degating and fettling, heat treatment, machining, finishing, and the handling and queue time between departments — with every step marked in-house or priced at your own accepted vendor's markup, then ranked cheapest, quickest and fewest-steps. The scope boundary becomes a line on a route rather than a position two departments hold.

#### How many days does an outsourced operation add to a part's lead time?

Queue days sit on the step itself, next to the markup, rather than in somebody's head. Handling and the transfers between departments are priced as real route steps too, and candidate routes are ranked by quickest as well as by cheapest, so the schedule cost of putting an operation outside is visible at the point the scope decision is made instead of when the promised date starts moving.

#### Where does a make-or-buy comparison stop being something software decides?

Vendor selection is the boundary. A sourced step is priced with one accepted vendor's markup, already set in your cost model — not a solicitation, not a marketplace, and not a market rate invented on your behalf. Which approved supplier is cheapest for a given operation stays a question for your own sourcing process; what gets priced here is the work and the days it takes.

#### Our plant has spare machines — how do we check it can hold the features?

Feature detection and a reach check answer that off the model. Holes, pockets, flats, bores and bosses come back each with a confidence, and a real voxel removal simulation against actual tooling shows exactly what stock is unreachable. Collision and fixture modelling are deliberately out of scope, so the result tells you what your tooling cannot get to, not whether a setup is safe to run.

## Explore further

- [For procurement — know what the part should cost before you negotiate](https://partimation.com/for/procurement/) — You buy parts you did not design, priced by suppliers whose numbers you cannot take apart. Partimation gives the buy side its own should-cost: an itemized ledger where every line names its rate or rule, a process verdict that names the constraint behind it, and the exact quantity where a cheaper method takes over.
- [In-house or send it out? Price the step instead of arguing about it](https://partimation.com/solutions/make-vs-buy/) — Whether a step runs on your own machines or goes to a vendor is usually judgment and a phone call. Partimation builds the full route — tooling, forming, heat treatment, machining, finishing and the transfers between departments — and prices each step in-house or at your accepted vendor's markup, with the queue days.

## Related pages

- [For procurement — know what the part should cost before you negotiate](https://partimation.com/for/procurement/)
- [In-house or send it out? Price the step instead of arguing about it](https://partimation.com/solutions/make-vs-buy/)
- [RouteDFM](https://partimation.com/routing/)
- [MachDFM](https://partimation.com/machining/)

## See what this looks like on your own parts

Send a model or a drawing and book a walkthrough — or start free and run one through yourself.

## Book a demo

Tell us about your shop and we'll set up a walkthrough on a real part.