Tuesday, November 2, 2010

Fender Washers

Fender washers are just flat washers with an oversize outside diameter. I imagine that the name comes from early days in the automobile industry, when cars' fenders weren't integrated with their bodies as they are on modern cars. Fenders were separate curvaceous sheet metal items that were bolted onto the corners of the body. Large diameter washers would spread out the clamping force of the bolts, and make for a more robust, fatigue-resistant attachment.

Applications for such washers crop up now and then. I've gotten the larger sizes (1/4" and up) at The Home Depot. If you save the knock-outs from electrical boxes, you'll have the makings for 7/8" diameter washers on hand. The knock-outs are suitable for screw sizes 6, 8 and 10, though they border on being a bit too large and ungainly-looking for No. 6 screws. Here's a photo, with one knock-out done as a No. 8 washer:

For rough work, you can just eyeball a centre punch position and drill the thing. For a good appearance, use a centre-finder to spot the true centre, drill a 3/32" pilot hole followed by the requisite size of drill for the screw. Deburr the hole and file off the burr that's at the edge from breaking out the knock-out.

Hole sizes are as follows:

No.6 -- 9/64"

N0. 8 -- 11/64"

N0. 10 -- 13/64"

A drill press vise makes drilling the things easy. Here's how it looks in action:

I wouldn't care to have to make 100 of the things this way, but for my usual requirement for one or a few, it's not at all impractical to do. And the price can't be beat; saves me money to spend on essential bad habits.

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