This is a closely controlled assembly. Very little dimensional change of the stack is accommodated. The small thickness of the dust cover is huge in proportion.
I do not have any feel for the thickness of the dust cover as compared to the cup of the Belleville ( spring, cup) washers. But I trust the factory design accounts for that. And that the other critical surface, where the anti spin washer would bottom out on the spindle, in most cases likely shows little wear on the shaft end.
I got interested in this topic because the setup seems so simple and I did not understand the purpose of the Belleville washers.
Belleville washers are not washers actually, but rather springs. As they are compressed they exert increasing force against the blade, which pushes against the dust cap. Friction between the components holds the blade stationary on the shaft.
Two washers stacked on top of each other in the same orientation doubles the amount of force pushing on the blade. If the two washers were stacked with their curves opposite the force would be halved. But the distance the springs acted over would be doubled.
The bolts that go into the spindle are torqued to about 80 lb-ft. Is this enough to cause the anti spin washer that slips over the shaft hex end to bottom out? Do not know.
Chances are pretty good that the set up is designed so if the anti spin washer is bottomed out when the 80 lb-ft of torque is applied to the spindle bolt, the Belleville washers are not totally flattened. They would then apply a given force to the blade, holding it stationary, but still allow some shock absorbing slip when something hard/solid is struck by the blade.
Like most springs, the cup washers can be reused multiple times unless damaged. But why should they be damaged? I speculate they are damaged when they slip to protect the other mechanical components in the system when something hard is struck.
I think the message here is to first be sure that if your mower calls for two spring washers, that you have two where required. Second is to torque the spindle bolts to the proper torque with a torque wrench. NOT an impact wrench.
Might be a good idea to inspect the anti spin washer to make sure the surface that pushes against the cup washers is not worn. If worn, flip it and replace it next time might be a temporary answer.
I have new blades coming, and ordered a bunch of M12 cup washers. Now looking forward to seeing what I find on my mower deck when I get home later in the week.
Bill
