Hello! Welcome back to your course on mechanical design.
In our last lesson, we started bringing assemblies to life with Revolute and Slider joints. You got a first taste of the As-Built Joint command as a convenient way to connect parts that you had already modeled in their final positions.
Today, we're going to formalize that concept. This lesson is dedicated entirely to the As-Built Joint, exploring the strategy of when and why it's the right tool for the job. Mastering this workflow is crucial for efficient assembly design, especially for the kinds of projects you're aiming for. Whether you're designing parts in context—like a custom bracket for your desk—or importing standard hardware like screws or bearings, the As-Built Joint is your go-to command.
By the end of this lesson, you will be able to confidently use the As-Built Joint to apply motion constraints to components that are already designed in their final assembled positions.
1. The Core Idea: "Joint" vs. "As-Built Joint"
The most important concept to grasp is the difference in workflow between the standard Joint command and the As-Built Joint command.
-
Standard
Joint: You use this when your components are modeled separately and are floating in space. TheJointcommand does two things simultaneously: it moves one component to align with another, and it defines the motion relationship between them. This is often associated with a "bottom-up" assembly approach. -
As-Built
Joint: You use this when your components are already in their correct positions relative to each other. The command does not move the components; it only defines the motion relationship. This is the primary tool for "top-down" design (where parts are designed in the context of the assembly) and for assemblies using imported parts (e.g., from a supplier website like McMaster-Carr or a file format like STEP).
Since your parts are already in place, the As-Built Joint dialog is simpler. It asks for the components and the type of motion, then a "snap" point to define the center or axis of that motion.
To see this difference in action, the following video provides a perfect comparison.
Fusion 360 - What is the difference between Joints and As-Built Joints?
This video from Mechanical Advantage clearly explains the difference between the two joint types and demonstrates when to use As-Built Joints. It also provides excellent examples of applying different motion types.
Please watch the following segments: Concept Explanation (03:17 - 03:55): Pay attention to the initial state of the model—all parts are in place but have no relationships. Applying As-Built Joints (03:55 - 07:35): Observe how Rigid and Revolute (with limits) joints are applied without moving any components from their starting positions. Final Recap (16:34 - 17:21): This is a concise summary of the core difference. Listen for the key takeaway: if the part is already where it needs to be, use an As-Built Joint.
2. A Powerful Companion: The Rigid Group Command
When working with imported assemblies, you'll often encounter a collection of parts that are meant to be fixed together, like a bolt with its nut and washers, or a pre-assembled caster wheel. Applying individual joints to all of these would be tedious.
This is where the Rigid Group command comes in. It lets you select multiple components and "weld" them together into a single, rigid unit. After creating a rigid group, you can then apply a single As-Built Joint to the entire group.
Let's watch a demonstration of the Rigid Group command. This video from Brad Tallis uses an imported toggle clamp to show how to quickly group parts before defining motion.
Watch from 01:08 to 06:05. Focus on two key moments: At 03:20, he creates a 'Rigid Group' to fix the handle grip to the handle arm. At 05:00, he groups the entire plunger sub-assembly together before applying a slider joint to it. Notice how this simplifies the process by reducing the number of joints needed.
This strategy of creating Rigid Groups first, then applying motion with As-Built Joints, is fundamental to efficiently adding intelligence to complex assemblies.
3. Hands-On Practice: Assembling a Tripod
Now it's time to put this all into practice. We'll use one of Fusion 360's built-in demo files, which is a perfect example of a multi-part assembly with all components designed in place. Your task will be to take this "dumb" model and make it fully functional using only As-Built Joints and Grounding.
This exercise will walk you through applying Rigid, Slider, and Revolute joints.
Day 23 of Learn Fusion 360 in 30 Days for Complete Beginners!
We will follow the excellent tutorial from Product Design Online. Please open the article and follow the steps below to work on the tripod file.
I will guide you through the relevant sections of this text. Follow these steps in Fusion 360. Open the File: Follow the instructions in the article under the heading 'Demo File – Tripod'. This will show you how to find the 06_tripod file in your Data Panel and save your own copy. Ground the Base: Before adding joints, you need a fixed anchor. Read the section titled 'Ground a Fusion 360 Component' (starts with 'When starting a new assembly...') and ground the red Stand component as instructed. Create Slider Joints: Follow the instructions under 'Slider “As-Built Joint”' (starts with 'The lower tripod legs should slide...'). Apply a Slider joint to one of the legs and define its motion limits. Note how this joint is automatically applied to the other two legs because they are copies. Create Rigid Joints: Follow the instructions under 'Rigid “As-Built Joint”' (starts with 'Let’s proceed by adding a ‘Rigid’ As-built Joint...'). Apply rigid joints to fix the rubber feet and the black connectors to the legs. Create Revolute Joints: Follow the instructions under 'Revolute “As-Built Joint”' (starts with 'For our final Joint on the lower assembly...'). Apply a Revolute joint to connect the leg assembly to the main stand. Set the joint limits as described. You will need to repeat this for the other two legs. Create a Ball Joint: To finish, follow the instructions under the heading 'Ball “As-Built Joint”' (starts with 'Lastly, we need to apply an “As-built Joint” to the top camera mount...'). This will create the final motion for the camera mount. Once complete, try moving the tripod legs and the camera mount. You should have a fully functional assembly!
Conclusion
Great work today. You've now formally learned one of the most important assembly workflows in Fusion 360. By understanding the distinction between a standard Joint and an As-Built Joint, you can build and define motion in your assemblies much more efficiently.
Key Takeaways:
- As-Built Joints are used when components are already modeled in their final assembled positions. They define motion without moving parts.
- This workflow is ideal for top-down design and for adding intelligence to imported assemblies (e.g., STEP files or vendor parts).
- The
Rigid Groupcommand is an essential partner to As-Built Joints, allowing you to bundle static parts into a single unit before defining motion. - The process for any As-Built Joint is: select components, choose motion type, and define the snap point (axis/center of motion).
In the next lesson, we will explore another crucial assembly tool: Section Analysis. Now that you can build assemblies with moving parts, the next logical step is learning how to look inside them to check for internal fit, clearance, and potential interference between components.