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Showing posts from October, 2007

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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...
NEW RELEASE: Stop trying to be a Hero. Start being a Mechanic. Get "The Sheet Mechanic" on Amazon »
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Column Design Guide: Euler vs. Johnson Buckling Equations

Figure 1: Buckling is a geometric instability failure, not just a material strength failure. In a mechanical design situation, the expected load on a column and its length are usually known. The designer's job is to specify the structural parameters to prevent failure. Advertisement The 5 Key Design Parameters End Fixity: How is the column attached? (Pinned-Pinned, Fixed-Free, etc.) This determines the effective length factor (K). Cross Section: The shape (I-beam, Tube, Solid Round). This determines the Radius of Gyration (r). Material: Determines Stiffness (Modulus E) and Strength (Yield Sy). Design Factor (N): The safety margin. Final Dimensions: The actual width/thickness required. Because the cross-section (Item 2) determines the slenderness ratio, but you can't pick the cross-section until you know the allowable stress, column design is inherently iterative . The Iterative Design Loop: 1. Assume a di...

Master Beam Theory: Stress & Deflection

Reactions are the forces and/or couples acting at the supports and holding the beam in place. In some cases, the user should enter a distributed load to account for the weight of the beam. The shear V effective on a section is the algebraic sum of all forces acting parallel to and on one side of the section: V = Σ F Advertisement The bending moment is the algebraic sum of the moments due to applied loads and other applied moments to one side of the section of interest. Using the value V , the bending moment can be calculated: M = ∫ (V · dx) + M 0 Where: • x = position on the beam measured along its length • M 0 = constant of integration evaluated from the boundary conditions. A bending moment that bends a beam convex downward (tensile stress on bottom fiber) is considered positive, while convex upward (compressive on bottom fiber) is negative. Figure 1: Coordinate system of a beam. Moment and shear diagram...

Engineering Guide: Bolt Selection, Clamping Force & Torque Calculation

Figure 1: A bolted joint works like a stiff spring. Tightening the nut stretches the bolt (tension) and compresses the parts (clamping force). 1. Bolt Selection for Required Clamping Force The primary goal of a bolted joint is to provide a required clamping force (F) between mechanical components to prevent separation or sliding. If a set of n bolts is used, and the total load is distributed equally, the required clamping load per bolt is: P = F / n Advertisement Defining Material Limits (Proof Strength) Bolts are selected from standard grades (e.g., SAE J429 Grade 5 or 8, ASTM A325). Instead of designing to the yield strength, bolt design uses Proof Strength (σ) . Engineering Insight: Proof vs. Yield Proof strength is slightly lower than yield strength. It is the maximum tensile stress a bolt can withstand without experiencing any permanent set. Designing to proof strength ensures the bolt remains entirely elas...