The Machine Parts Factory is the 4th 'Production' building you unlock.
Usefulness[]
This building produces machine parts from stone. Normally, it requires 3 stone to make 1 machine part, but Scrap Metal Recycling can reduce the number of stone used to 2. Building Modes also affect how much Resources you make and lose and also affect the resource production work speed .
Also, when it is next to a mechanical house, the quality of the house goes from 30 to 80.
When functioning, it appears to drop lava/molten something onto incoming rocks and then crush them with pistons.
Building Modes[]
Building Modes can increase the work speed or increase production of a certain resource. Certain building modes have upsides and consequences (Turbo Boost building mode), such as Increasing the resource production work speed, but using up more resources and reducing the production of other resources. The Building modes include Enable Factory (work normally), Turbo Boost (the factory works faster but costs 2 more stone for every machine part), and Disable Factory (factory does not produce machine parts).
Turbo Mode is useless with Scrap Metal Recycling. Say it uses one stone every second. Then Enable Factory would make one machine part every 2 seconds, and use one stone every second. A however, on turbo mode it will still make one machine part every 2 seconds, but it will consume more stone.