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Showing posts from August, 2011

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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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Column Design Guide: Euler vs. J.B. Johnson Formulas (Part 3)

Figure 1: The Column Constant (C c ) marks the boundary between Inelastic Buckling (where material yielding dominates) and Elastic Buckling (pure instability). The Great Divide: Long vs. Short Columns In Part 2 , we learned how to calculate the Slenderness Ratio (Le/r) . This ratio tells us the geometry of the column. However, geometry isn't enough. We also need to account for the material properties. A steel column behaves differently than an aluminum one. To decide whether to use the Euler Formula (for elastic instability) or the J.B. Johnson Formula (for inelastic buckling), we must calculate a transition value known as the Column Constant (C c ) . Advertisement Search for Mechanics of Materials Books Calculating the Column Constant (Cc) The Column Constant represents the specific slenderness ratio where the critical stress equals half of the material's yield strength. It is the borderline between ...

Column Design: Effective Length and Slenderness Ratio (Part 2)

Figure 1: The "K" factor adjusts the actual length based on how rigid the supports are. Fixed ends (rigid) make the column effectively shorter and stronger. The Critical Factors in Buckling In Column Design (Part 1) , we established that a column will buckle around its "weakest" axis—the one with the minimum radius of gyration ( r min ). However, the geometry of the cross-section is only half the story. The way the column is held at its ends (its boundary conditions) dramatically affects its strength. This introduces the concept of Effective Length . Advertisement Search for Machine Elements Design Books 1. Effective Length (Le) The effective length is not always the actual length of the column. It is the length of an equivalent pinned-end column that would have the same buckling load. We calculate it using the formula: Le = K × L Where: L: The actual unsupported length of the colu...