nThe most important feature of the cam design is the choice of the lock angle between horizontal and the contact point shown below.n
If you Probe the reaction force, the 1250 N upward force on the granite creates a 5200 N side force. If the Coefficient of Friction is greater than 0.24 then the cam will not slip. If the lock angle was reduced from 13 degrees to 6 degrees, then the coefficient of friction needed to prevent slipping would be reduced to 0.1nThe cam has been designed to maintain that lock angle for a range of crack widths.n
If the lock angle gets too close to zero, there is a failure mode where the contact point rotates past horizontal and there is suddenly no support. The contact point could do that if the cam body is too flexible and elastically compresses enough to allow that to happen, or if the cam body is not strong enough, the stress goes past yield and plastic deformation allows that to happen. Or if the crack faces open up.nIn the lightweight design with holes in the part, the flexibility and strength of the cam varies as a function of crack width as different parts of the cam make contact and there is more or less material between that point and the pivot hole. The load to pull the contact point past horizontal is much lower with the lightweight design than the solid design.n
To determine the failure load that pulls the contact point past horizontal, the pin must be included in the analysis, since that can deform and is not represented in this idealized analysis. nIf the lock angle was designed to be very large, like 45 degrees, then the cam does not generate enough side force to support the load without a very high coefficient of friction, which is 1.0 for a 45 degree lock angle. At lower coefficients of friction, there is no support from the beginning, the cam just slips and does not grip.n
If you Probe the reaction force, the 1250 N upward force on the granite creates a 5200 N side force. If the Coefficient of Friction is greater than 0.24 then the cam will not slip. If the lock angle was reduced from 13 degrees to 6 degrees, then the coefficient of friction needed to prevent slipping would be reduced to 0.1nThe cam has been designed to maintain that lock angle for a range of crack widths.nIf the lock angle gets too close to zero, there is a failure mode where the contact point rotates past horizontal and there is suddenly no support. The contact point could do that if the cam body is too flexible and elastically compresses enough to allow that to happen, or if the cam body is not strong enough, the stress goes past yield and plastic deformation allows that to happen. Or if the crack faces open up.nIn the lightweight design with holes in the part, the flexibility and strength of the cam varies as a function of crack width as different parts of the cam make contact and there is more or less material between that point and the pivot hole. The load to pull the contact point past horizontal is much lower with the lightweight design than the solid design.nTo determine the failure load that pulls the contact point past horizontal, the pin must be included in the analysis, since that can deform and is not represented in this idealized analysis. nIf the lock angle was designed to be very large, like 45 degrees, then the cam does not generate enough side force to support the load without a very high coefficient of friction, which is 1.0 for a 45 degree lock angle. At lower coefficients of friction, there is no support from the beginning, the cam just slips and does not grip.n
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