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...
Figure 1: Fundamental deviations for shafts and holes relative to the Zero Line. (Click image to search for the Standard Reference ) In the world of Precision Metrology and CNC machining, adhering to the ISO 286 standard for limits and fits is non-negotiable. Whether you are designing a bearing press fit or a sliding shaft, understanding these metric standards is the difference between a smooth assembly and expensive scrap. Essential Reference: Most professional engineers rely on the Machinery's Handbook for the complete tables of tolerances and allowances. It is the industry standard for verifying these calculations. Advertisement 1. The Big Picture: Hole Basis vs. Shaft Basis Before calculating numbers, you must choose a system. Hole Basis System (Most Common): We keep the hole size constant (e.g., exactly 20.00 mm with a tolerance of H7) and machine the shaft to fit. This is preferred because drills and reame...