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Posted by David Sherman on Thursday, April 23, 2009 at 23:47:56 :
In Reply to: Re: Square washers posted by Nick on Thursday, April 23, 2009 at 23:01:16 :
The square washers were primarily designed to hold sheet metal against a solid base. The inside teeth lock into the head like a normal inside-tooth lock washer, and the large outside area spreads the load around on the sheet metal. You can still get inside/outside toothed lock washers, but that's not really the right idea and the outside teeth are ugly. I haven't even found any large-diameter round inside-tooth lock washers.
For practical purposes, a belleville washer would probably do the job, both spreading the load and keeping the bolt from vibrating loose. Engineers used to think that the teeth on a lock washer dug into the metal to keep the nut or bolt from unscrewing, but it turns out that the way they really work is to maintain a pre-load on the threads to that there's always some frictional contact to keep the parts from unscrewing. That's why split lockwashers works as well or better than star lockwashers. Even though a belleville washer doesn't have any teeth, it would probably work fine just by maintaining a pre-load.
Of course that's only a practical solution, not an authentic one. An M-series truck just wouldn't look right without the square lock washers. My M43 ambulance must have 10 times as many as a plain M37, which is why I set out to find the actual washers. I bought a box of one size from one of the surplus dealers. Some guy on this forum once claimed to have buckets of some other size. It doesn't help that the hardened teeth of the washer bend in under the bolt head making it impossible to remove and re-use the washer when replacing a rusted or stripped bolt.
Perhaps one of the major dealers with more money, customers, and ambition than I have could figure out exactly what sizes are 100% correct (WCL's catalog lists various thicknesses in each diameter) for the M-series trucks, and pay whatever it takes to get WCL to do production runs and re-make the tooling while they at least still have the drawings and people who know how to do it. Or, maybe they could create new drawings from the old parts and get some Chinese outfit to make the washers. I'm sure the patents have long-since expired. Either way, the washers wouldn't be cheap, but since the surplus sources seem to be drying up, that might be the only way to get "correct" ones in the future.