The low flexural rigidity of auger conveyors often results in the critical speed for transverse vibrations occurring well within the working speed range of the conveyor. Operation at or near the critical speed should be avoided, not only for the safeguard of the conveying machinery itself, but also because of the increased damage which is inflicted upon the material being conveyed. It is shown that the computation of critical auger speeds can be carried out, with sufficient accuracy for practical purposes, by neglecting the stiffening effect of the helical auger blade. An approximate theoretical analysis of the blade stiffness is presented which serves to explain why the stiffness is negligible in certain cases. An experimental study was performed to correlate the theory and to obtain critical speed measurements of a 6 in auger for comparison with values computed from a theoretical equation. © 1965.