For engineers who already know the math—but still lose projects. For the last few years, I’ve been sharing technical guides here on Mechanical Design Handbook —how to size a motor, how to calculate fits, and (as you recently read) how to choose between timing belts and ball screws. But after 25 years in industrial automation, I realized something uncomfortable: Projects rarely fail because the math was wrong. They fail because: The client changed the scope three times in one week. A critical vendor lied about a shipping date (and no one verified it). The installation technician couldn’t fit a wrench into the gap we designed. University taught us the physics. It didn’t teach us the reality. That gap is why I wrote my new book, The Sheet Mechanic . This is not a textbook. It is a field manual for the messy, political, and chaotic space between the CAD model and the factory floor. It captures the systems I’ve used to survive industrial projec...
Let's continue from the previous post. Now it's time to visualize our previous calculation for the timing diagram of the indexing mill and punch die using 3D Motion Simulation in Unigraphics (UG) NX4.
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While we successfully created a 2D motion simulation in Excel, modern engineering demands a full Digital Twin. The UG NX4 Assembly model is prepared as shown below.
The mating conditions of the assembly model follow the sketch shown in [Timing Diagram (Part 1 - No Overlap Movement)].
Step 1: Entering the Simulation Environment
New to UG NX4 Motion Simulation? No problem. Follow this step-by-step guideline.
In the motion simulation environment, all commands are initially disabled. You must right-click on the assembly file and select New Simulation.
This command creates the necessary files and organizes them automatically.
Step 2: Defining the Kinematic Environment
Click the environment command (calculator icon) and select "Kinematics".
Why? Because we are going to use "Spreadsheet Run" to control the motion based on our Excel calculations, rather than relying on the internal dynamic solver.
Step 3: Creating Links and Joints
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Defining Links:
1. Click the Link command.
2. Select the object (the indexing mill).
3. Enter the name "Mill".
4. Click Ok.
Repeat this for the punch die. Now we have 2 links, but they are floating in space. We need to define joints to constrain their Degrees of Freedom (DOF) to zero.
Defining the Revolute Joint:
1. Select the Joint command.
2. Choose "Revolute joint" (allows rotation in Z-axis only) and select the "Mill" link.
Setting Orientation and Origin:
3. Select "Orientation of joint on the first link".
4. Select "Vector" and click the top face of the indexing mill (defines Z-axis).
5. Select "Point" and click the center of the mill.
6. Rename the joint to "J_Mill".
Step 4: Setting the Initial Motion Driver
The joint is defined geometrically, but it needs a Driver to move.
For now, we set a placeholder constant velocity:
1. Select "Constant"
2. Enter "100" in the Velocity box (100 deg/s).
Note: You are correct that the real motion should be cycloidal. We use this placeholder just to verify the mechanism is assembled correctly before we inject our complex Excel data.
Let's take a break. In the next post, we will replace this constant driver with our Spreadsheet Run data.
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