Staff / Principal Mechanical Design Engineer

Location: Los Angeles, CA (In-Office) | Full-time About the job The opportunity LettrLabs is rebuilding itself as an AI-native company, and engineering is where that change goes deepest. We built our own engineering design harness: an AI system that works hand-in-hand with engineers to take requirements and carry a design all the way to final, producible parts, much faster than a traditional workflow. We are looking for a Staff or Principal Mechanical Design Engineer to do two things at once. You will design LettrLabs' next-generation production automation platform. And you will shape the harness itself, deciding how real engineering judgment gets encoded into a tool that makes every engineer here faster. This is a rare chance to define how hardware gets designed in the AI era, while shipping real machines to a real production floor, at a pace traditional workflows can't match. This is a hands-on, individual contributor role reporting to the CTO. It is on-site in Los Angeles, in the office five days a week. What you'll do Own the mechanical design of LettrLabs' production process machinery and next-generation automation platform as we work to fully automate our production, from open-ended problem statement through build, commissioning and deployment of production machinery on our floor. Turn ambiguous business and operational needs into clear system and subsystem requirements, then generate concepts, run trade studies and drive down-selection. Take designs through architecture to release, using our design harness as your primary toolchain. Drive material and process selection for performance, cost, manufacturability and service life. Define and run validation: analysis, prototyping, test plans and design reviews that prove the design works before it ships. Act as a principal user and co-designer of our design harness. Find where it falls short, define what good looks like, and work with our AI and software engineers to iterate and build sound engineering practice into it. What we're looking for 7 to 15+ years in a design-centric engineering role, primarily mechanical. Mechatronics/aerospace backgrounds with a strong mechanical core are welcome. Level (Staff or Principal) will be set based on experience and fit. A track record of designing complete systems end to end, through production, commissioning and deployment. You have seen your hardware run, broken it and fixed it. Deep experience with a phase-gate or stage-gate design process: requirements, concept, trade studies and down-selection, preliminary and critical/detailed design reviews (PDR, CDR/DDR), and release. Strength in turning open-ended problems into clear, testable requirements and concepts at the system and subsystem level. Deep knowledge of metals, polymers and composites, and sound judgment in material and process selection. Strong mechanical fundamentals: statics, dynamics, mechanics of materials, tolerancing, mechanisms and DFM/DFA. You make quick, pragmatic calls from first principles, then drill into analysis or test to close and validate the design. Rapid, AI-driven development depends on this judgment. Nice to have Experience at a hard tech company known for engineering rigor and speed, such as aerospace, automotive, robotics, or industrial and factory automation. Background in production automation equipment, motion systems, or high-throughput machinery. <li data-local-id="b5e16e86-c64c-4855-9e16-1aabaa89e83b" data-prosemir