If the screw is not going in straight, the bottom of the screw head will contact one side of the washer first, and possibly spread the force to the rail in a wider area...but still to the side first contacted. Dan On Aug 21, 2008, at 7:39 PM, Fred Sturm wrote: > On Aug 20, 2008, at 8:56 PM, Chris Solliday wrote: > >> even with the panheads the non uniformity of the threads can throw it >> of if >> you tighten down even alittle too much. I use the washers even with >> the >> pans. >> Chris Solliday > > > Hi Chris, > I'm not following you. As far as I can see, a washer will spread the > pressure of the head over a larger area, assuming it is larger than > the head. But it would apply pressure to the flange in exactly the > same alignment, it wouldn't change the direction in which the screw > head was bearing on the flange. The washer is flat and acts as if the > screw head was that much thicker, or at least that's how I think of > it. > In my mental picture, the only thing that will cause the flange to > tip on the rail (assuming the rail is flat and clean, and the flange > bottom is too) is a screw hole drilled off center (fore or aft) or at > an angle. I don't see how any difference in the screw threads could > affect this, or could cause a flange to tilt when over tightened. > I can see potential benefits to adding a washer. The wood won't be > crushed as much, for one (the washer protects the wood from the > twisting action of the screw, and if it is larger, spreads the > pressure over a larger area). OTOH, if there is a small discrepancy in > the angle of the hole, the screw head tends to dig in and crush the > related side of the flange, which in my mental picturing, helps to > adapt things and level the flange. I see flanges where one side of the > screw head has made a bigger indentation, and assume that is what is > happening. > Maybe the esteemed Mr. McMorrow had it all figured out as Alan > reports, and I've been missing out on the answer all these years > because I was a cheapskate and didn't buy his book. Anyway, I can't > say as I have seen a really clear analysis of what goes on and why > (hence my earlier post giving my own take on it). > > Regards, > Fred Sturm > University of New Mexico > fssturm at unm.edu > >
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