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Why I Wrote The Sheet Mechanic (And Why Calculations Aren’t Enough)

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...
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NX Motion Simulation: Integrating Excel Timing Diagrams - Part 1

During the process of timing diagram design, I normally start with detailed calculations in an Excel spreadsheet to minimize acceleration while satisfying the required process cycle time.

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Once I can visualize the preferred displacement, velocity, and acceleration profiles of the mechanisms in Excel, the question becomes: What's next? Shall I start manufacturing immediately?

The answer is NO. In modern engineering, we use Digital Twin Technology to verify the design first.

From Excel to 3D Simulation

Currently, I use Unigraphics (UG) NX4 (now Siemens NX) to design the mechanical parts. When the assembly modeling is done, I use the assembly model to simulate the movement of mechanisms with the Motion Simulation Module.

This step is critical for Virtual Commissioning. It helps confirm the timing diagram before releasing the design for manufacturing. It is especially useful when movements are combined in 3D space, allowing me to detect interference (collisions) with other mechanisms and solve them proactively.

The Challenge: ADAMS Functions vs. Excel Data

When I first started using the UG NX4 Motion Simulation Module, I found it easy to set the links and define joints. However, I found it difficult to define the driver functions using ADAMS-General built-in functions.

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These functions are powerful for "Dynamics" environments, but often I prefer "Kinematics" because it's fast and focuses purely on displacement.

Can you imagine how difficult it is to manually write fifth-degree (3-4-5) polynomial cam functions for 3-4 different sectors inside this function editor? It is prone to syntax errors and is tedious to debug.

The Solution: "Spreadsheet Run"

I'm still familiar with using Excel spreadsheets to calculate things. It's easier if I can use the motion table that I've already generated during the design phase.

I finally found out that besides "Animation" and "Articulation", UG NX4 has command features called "Graphing" and "Spreadsheet Run".

These 2 commands allow me to import the Excel data directly to drive the simulation without entering complex functions manually.

The Workflow:
  • Calculate profiles in Excel (Cycloid, Polynomial, Linear).
  • Copy & Paste the values into the NX Spreadsheet Run tool.
  • Visualize the 3D motion instantly.

If the timing diagram is wrong, I just modify it in Excel and re-paste. This rapid iteration is the core of Computer-Aided Engineering (CAE).

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