This makes sense for rocket engines, which are mostly rigid objects with a lot of internal plumbing.  3D printing is good at objects with complex internal voids. The rigid parts can be made up as one piece, rather than welding or bolting a large number of parts together. The surface finish of the plumbing usually isn&#x27;t critical, so there&#x27;s no need for finish machining.  It&#x27;s the right tool for the job.<p>Here&#x27;s Space-X&#x27;s 3D printed engine.[1]  Watch the video of the test firing. The engine is being throttled up and down, at higher and higher rates.  Those guys like aggressive control strategies, as seen with the Falcon booster landing, and an engine which can keep up helps.<p>[1] <a href="http:&#x2F;&#x2F;www.spaceflightinsider.com&#x2F;organizations&#x2F;space-exploration-technologies&#x2F;spacexs-superdraco-engine&#x2F;" rel="nofollow">http:&#x2F;&#x2F;www.spaceflightinsider.com&#x2F;organizations&#x2F;space-explor...</a>