Bent crankshaft, or the blade is not installed properly
How do you change the blade on a Toro 21" self-propelled mower
blade might be out of balance
The handle, the bow and the blade.
The blade of a gravity knife is contained within the handle of the knife. It requires a spinning motion or gravity for the blade to come out of the handle.
Unscrew the handle to relive the tension on the saw. Remove the old blade, hook the new blade over the pins on the saw and tighten the handle back up.
A handle with a blade in it.
under the mower above the blade should be a allenhead plug
handle, blade and iron frameANS 2 - There are some really nice ones now. My current favorite is a German one that has a tubular steel frame, really light weight and keeps the blade very tight due to it's shape. -See the current Lee Valley catalogue.
A stone age axe blade.
the tang
A tool that has a curved blade and a small handle.
The handle unscrews which releases the tension on the blade. There is a pin through each end of the blade that slips into a notch in each end of the handle.