DOWEL PINS IN ASSEMBLIES Machinery's Handbook, 31st Edition
1886
Fig. 2. Four Options for Dowel Pin Installation Option A: In the lower plate the dowel is a light press fit which means that there is 0.0002 to 0.0005 inch interference between the dowel and the hole. The hole in the bottom part of the lower plate is made 0.03 inch smaller than the dowel hole to prevent the dowel from falling out while providing a knockout hole for a punch. The top plate also has a stepped hole that is 0.0002 to 0.0005 inch larger than the dowel for a slip fit, and a larger diameter for a relief. The relief is 0.03 inch larger than the dowel. It is a good practice to relieve por tions of the hole that are not used for locating. Dowels should be installed with two times their diameter as a bearing surface. In other words, a 3 ⁄ 8 -inch diameter dowel should con- tact the hole for 3 ⁄ 4 of its length in each component. A 1 ⁄ 4 -inch dowel should contact each plate for 1 ⁄ 2 inch of the dowel’s length in each component. Option B: In this example the design does not permit the dowel hole to go through the lower plate. Since pressing dowels into blind (dead end) holes is not recommended, the dowel is a slip fit in the lower plate and a press fit in the top plate. Again, the top plate is relieved allowing the dowel the proper amount of effective engagement. Option C: This example is the opposite of Option B. A knockout hole which is 0.03 inch smaller than the dowel is provided in the lower plate. The press fit is in the lower plate, the slip fit is in the top plate because it is very difficult to remove a dowel that is pressed in a blind hole. Option D: In the event that through holes are not permitted in either plate, both sides are made to a slip fit for the dowel. American National Standard Straight Pins.— The diameter of both chamfered and square end straight pins is that of the commercial wire or rod from which the pins are made. The tolerances shown in Table 4 are applicable to carbon steel and some deviations in the diameter limits may be necessary for pins made from other materials.
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online