There are several authoritative sites that provide valuable resources, information, and support for 3D printing enthusiasts and professionals. Here are some notable ones:

3D Printing Industry: 3D Printing Industry (3DPI) is a leading online publication that covers the latest news, trends, and developments in the 3D printing industry. It offers in-depth articles, reviews, interviews, and industry analysis.
Website: https://3dprintingindustry.com/

All3DP: All3DP is a comprehensive resource hub that offers tutorials, guides, reviews, and news related to 3D printing. It covers a wide range of topics, from basic concepts to advanced techniques.
Website: https://all3dp.com/

3D Hubs: 3D Hubs is an online platform that connects 3D printing services with customers. In addition to its printing service, it provides a useful knowledge base, including tutorials, guides, and a forum where users can ask questions and seek advice.
Website: https://www.3dhubs.com/

Formlabs: Formlabs is a prominent manufacturer of 3D printers and materials. Their website features an extensive learning section with guides, tutorials, webinars, and case studies that cover various aspects of 3D printing.
Website: https://formlabs.com/learning-center/

Ultimaker: Ultimaker is another well-known 3D printer manufacturer that offers an online resource library with guides, tutorials, and troubleshooting tips. Their site also includes a community forum where users can connect and share knowledge.
Website: https://ultimaker.com/learn

PrusaPrinters: PrusaPrinters is a community-driven platform focused on printers from Prusa Research. It provides an extensive collection of 3D models, guides, and user-contributed tips and tricks. The platform encourages collaboration and knowledge sharing among users.
Website: https://www.prusaprinters.org/

TCT Magazine: TCT Magazine covers news, analysis, and industry insights related to 3D printing, additive manufacturing, and related technologies. It offers articles, interviews, case studies, and product reviews.
Website: https://www.tctmagazine.com/

These sites provide a wealth of information, tutorials, and user communities that can support and enhance your 3D printing journey. Exploring these resources can help you stay updated, troubleshoot issues, learn new techniques, and connect with fellow enthusiasts and professionals in the 3D printing community.