7 years ago

FALL 2014

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Distributor's Link Magazine Fall Issue 2014


56 THE DISTRIBUTOR’S LINK Spirol International Corporation 30 Rock Avenue, Danielson, CT 06239 Tel: 1-860-774-8571 Fax:. 1-860-774-2048 Email: HOW TO PROPERLY PIN A SHAFT & HUB ASSEMBLY by Caroline Mallory, SPIROL Application Engineer One of the primary benefits of using a Coiled Spring Pin to affix a hub or gear to a shaft is the Coiled Pin’s ability to prevent hole damage. Another benefit is that the Coiled Pin absorbs wider hole tolerances than any other press-fit pin. This translates to lower total manufacturing costs of the assembly. There are a few design guidelines that must be adhered to in order to achieve the maximum strength of the pinned system and prevent damage to the assembly: The design guidelines can be divided into two groups: 1) the shaft and hub, and 2) the pin. Shaft and Hub Considerations The hole in a shaft should not exceed 1/3 of the shaft diameter. For mild steel and nonferrous shafts, standard duty pins are recommended. The extra strength of a heavy duty pin is only beneficial if the hole is less than 1/4 the diameter of the shaft or if the shaft is hardened (Figure 1). It is recommended that the hub be designed with a minimum wall thickness of 1.5 times the diameter of the pin. Otherwise, the strength of the hub will not match the shear strength of the pin (Figure 1). As the wall thickness of the hub increases, so does the area of material around the pin. The diameter of the holes through both the shaft and hub should be precision matched to eliminate any movement of the pin within the holes. It is recommended that the difference between the hole diameters in the hub and shaft not exceed 0.05mm (.002”) to prevent movement of the parts relative to each other. Otherwise, the pin will be subject FIGURE 1 to dynamic loading such that a very small change in velocity could equate to a significant change in force impacting the assembly. The hole should be centered in both the shaft and hub to prevent stress concentration and ensure there is enough material around the pin to withstand the applied forces. If the holes cannot be precision matched, dividing the tolerance between the shaft and hub is recommended. The larger half of the tolerance should be applied to the component with the longest engagement length, and the smaller half should be applied to the other component. Countersinks on the holes are not recommended. In addition, the outer diameter of the shaft (OD) and the inner diameter of the collar (ID) should be designed such that the distance between the shear planes (OD-ID) does not exceed 0.13mm (.005”). In both cases, an unsupported length of pin in an area where torque may be applied is created. This could cause a bending moment, which shortens the lifespan of the pin (Figure 2). FIGURE 2 A countersink increases the distance between the shear planes. This can put the pin in bending and thus reduce the strength of the pin. please turn to page 216


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