The blade on my Craftsman circular saw will not tighten down and consequently slips on the spindle. I've tried packing the bolt with a washer and it didn't help. Can't find anything online so this may not be a typical problem. Could it be as simple as replacing the spring washer? Any feedback would be appreciated.
Make a shim out of thin cardboard and place it between the inner blade washer and the blade. The blades they're making these days are thinner than the older blades and some of the older saws have to be shimmed in order to prevent blade slippage.
A very thin kerf blade might spin, if the inner and outer nuts connect before clamping the blade.
Some (most 7 1/4 inch) blades have a diamond knockout that allows it to be used with a larger shaft. If this were not in place, it would make it hard to align and tighten (would be dangerous).
I just recently had the same issue. As simple as it sounds, try using a tap on the bolt/nut. I had the slightest bit of debris or thread preventing the bolt from making it tighten all the way, which caused resistance and caused the spindle to run while trying to tighten.
Based on your description, I guarantee this is your issue.
Sorry if this is too simplistic, are all the pieces there?
There is an inner drive washer with flats to engage the shaft and usually has a serrate waved surface.
Next comes the blade.
Then an outer drive washer
And a bolt with a spring-plate permanently attached lock washer.
There is a spindle lock button you use to hold the shaft when you tighten the bolt.
Under normal operation, the blade should be gripped with enough force to drive it except when you dog the blade down hard into material and jam it from turning. Works kind of like the shearable key on a lawnmower, give to prevent sudden stoppage.
Something I did not see here: My SKIL 7-1/4" circular saw from about 1978 (still working) came with instructions to NOT overtighten the blade. Rather, brace the blade from turning; hand-tighten the bolt and washer; then wrench-tighten the bolt ONLY 1/8 turn further. This allows the blade to slip, deliberately, if it binds in the material. It's a safety feature. (Oddly, the Craftsman saw I bought this year only says to OIL the washers where they grip the blade, but does not explain about binding and allowance for blade slippage.)
Easy fix for your slipping blade make sure saw is unpluged take the bolt and tension washer off and leave blade and top washer on .I used my cutoff tool to remove the proud part of the shaft . The amount I removed might have been 1/64 to 1/32 . Saw works great now. The saw is old so I didn’t mind experimenting on it .
Why again do you want to tighten down a circular saw blade??
Perhaps I am missing this as I only skimmed across the question, stealing time at work to research power tools.
One thing I learned when training to become a journeyman carpenter was that you do not want to tighten more than 1/4 turn as this is the safety. Better to have the blade spin to a stop than to tighten hard a blade and hit a knot and have the blade kick back off your work and hit yourself in the thigh.
maybe way to old but inner washer might be upside down