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big fred
08-28-2002 11:10:54
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Re: Nuts, bolts, and washers in reply to Paul (QC), 08-28-2002 08:25:46
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The purpose of a washer is to distribute load and protect surfaces. If the bolt goes thru fiberglass, sheetmetal, wood, etc, which doesn't have a lot of strength or is fairly soft, you need to distribute the load over a larger area, so you select a washer to do that. If you have a surface with some special finish on it, e.g. Alodine on aluminum, you might want to add a washer to keep the bolt head or lockwasher from damaging the finish and creating a place for corrosion to develop. Also, when fastening dissimilar metals, you may need to select a washer to reduce the effects of galvanic corrosion. And washers can be used (like fender washers) to help account for a lot of slop built into mating parts to allow for alignment, or conversely, on tight tolerance holes with high-tensile bolts, a countersunk washer may be used to keep the radius between the bolt head and grip from riding on the edge of the hole. Generally, though there are some exceptions, you won't hurt anything by adding a flat washer. I find that our electronics factory will sometimes add a washer even when we don't show one on our drawings, depending on the assembler. Some do, some don't, drives the inspectors nuts.
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