[LeifCarrotson]

I did engineering at a firm that built all its own machines for PC-based industrial testing equipment, about 50 per year.

It was totally not worth it for us, it was penny-wise and pound-foolish. We switched to buying some Advantech machines, and while the BOM cost was one $1200 line item compared to a long DIY BOM off pcpartpicker.com that ran closer to $600, all the engineering time we wasted on component selection and ordering and progress bars and BIOS configs and Windows update and cable ties and debugging reliability issues was much harder to quantify and probably significantly more than $600.

I think there's a few inflection points on the quantity/process value curve - Building 4 machines? That's a little one-day project for somebody. Building 400? Hire a technician, set up an assembly station, and develop some work instructions. Building 40? That's going to have one or two that need warranty work, and you're not going to recoup the investment required to develop a good process - just buy them from someone who has. Building 4000? Your process is now multiple technicians, an engineer, a purchasing agent, and some management, and support needs after-hours on-call people, and you need an inventory of spare parts...developing that capability is again more expensive than just buying it. Building 40,000? At that level, you're building a PC-construction business and you can sell your spare capacity to the 40-unit guys.