Help understanding forces on a jigsaw blade?

[TheRB4891]

I am struggling to understand whether a jigsaw blade which should be operated perpendicularly to the cutting surface needs to resist shear force?

Anything obvious i have missed would be appreciated!

Thanks

 

[coolbackyard]

Typically, if the blade is kept from being bent in any way during operation, the only shear forces acting on the blade will be on the teeth themselves (undergoing shear and bending moment). This is the case if you are cutting perpendicular to a sheet of plywood or such. Further consideration must be made if you are cutting through multiple surfaces, such as bonded plywood sheets, etc. If the boards or whatever have some lateral forces acting on them in relation to one another, shear stresses will be involved (think: cigar cutter). For thicker cutting blades, shear WILL become an issue. There are frictional forces acting along the surface of the sides of the blade, which cause shear and bending, but there are typically two simplifying assumptions to overcome this. First is that the frictional forces have almost zero moment arm length (think: the distance from the surface of the blade to the middle of the blade as almost zero). The second is that the teeth of saw blades are generally either wider than the main portion of the blade, or slightly bent outwards alternately. This means that the main body (part of the blade w/o teeth) has a small gap between its sides and the material being cut, eliminating those frictional forces altogether.