Interference fit, transition fit, and clearance fit are the three basic fit relationships in mechanical design. Many people only consider tighter fit for interference fit, looser fit for clearance fit, and neither tight nor loose fit for transition fit when designing products, but is that enough? Of course not. There are still many issues that need to be considered behind these fit relationships, especially interference fit, which is the most prone to problems. Today, I will give you examples of precautions for using interference fit relationships.
Matters to be noted for interference fit: 1. When the shaft hole has an interference fit, it must have a guiding function, that is, it needs to have a chamfer (the hole and shaft must have a certain chamfer, that is, the entrances of the two matching parts should be chamfered, or a conical surface that plays a guiding role). 2. There must be a clear positioning mechanism between the interference fit parts (shaft shoulders, bosses, etc. must be designed to ensure the depth of the product interference fit). 3. Avoid pressing two interference surfaces at the same time (if two interference fit surfaces are pressed in at the same time or almost at the same time, assembly is very difficult, and the other matching surfaces should be designed to be pressed in one by one). 4. When the conical surfaces are matched, there must be no positioning structure (if the end faces are positioned, there may be a gap between the two conical surfaces and the matching relationship will be lost). 5. When installing interference fit in blind holes, air should be exhausted. If a closed space is formed inside the hole, installation will be difficult. When pulling out, a vacuum will be formed inside, making it even more difficult to pull out. In order to avoid the formation of a closed space, small holes or inner grooves for ventilation must be set (this will also facilitate mold demolding). 6. Deep interference fits on shafts of the same size are difficult to embed and unload. The length with interference should be limited to the necessary minimum size, and other parts should have a slight gap to facilitate embedding; (In addition, if the machined shaft is long, only the precision of the matching relationship part should be designed to meet the requirements, and other parts should be made larger or smaller with lower precision according to the structure. This makes processing convenient and costs easy to control).
