If you're working on game development using Source SDK, you may need to export 3D models in OBJ format to use them in your projects. Here's a step-by-step guide on how to do it:

1. Install the Source SDK: First, make sure you have Source SDK installed on your computer. You can download it from the official Steam website.

2. Prepare your 3D model: Open your Source SDK project and locate the 3D model you want to export. Make sure the model is properly textured and positioned in the game environment.

3. Launch Hammer Editor: Open the Hammer Editor tool within Source SDK. This is where you'll be able to export your 3D model in OBJ format.

4. Select the 3D model: In the Hammer Editor, select the 3D model you want to export. Make sure it's properly selected and positioned within the editor.

5. Export as OBJ: Once the model is selected, go to the File menu and find the Export option. Choose to export the model as OBJ, and save it to a location on your computer.

6. Import into 3D software: After exporting the model as OBJ, you can now import it into your 3D modeling software, such as Blender. Open Blender and import the OBJ file to start working with the 3D model.

7. Edit and optimize: Once the OBJ file is imported into Blender, you can edit and optimize the 3D model as needed. This may include adjusting textures, smoothing surfaces, or making other modifications to the model.

8. Save and use: After making any necessary edits in Blender, you can save the 3D model in a format compatible with your game development project. This may include formats such as FBX or DAE, depending on the requirements of your game engine or development environment.

By following these steps, you can successfully export 3D models in OBJ format from Source SDK and use them in your game development projects. Whether you're creating custom assets or modding existing content, this process will allow you to bring your 3D creations to life within the Source engine.