In micromachining, the uncut chip thickness is comparable to the tool edge radius, and chip won’t be generated if the uncut chip thickness is less than a critical value, besides that, the minimum uncut chip thickness affect many factors such as the cutting force, the chip’s modality, the cutting surface quality, etc. In this paper, a geometric model is developed to predict the minimum uncut chip thickness values. The model accounts for the theory that the critical condition of producing chip is when the friction of the surface deformation asperities is zero. Two situations when the minimum value is larger or smaller than the tool edge radius respectively to predict the minimum value are discussed. The influences of tool edge radius and material’s property on the minimum uncut chip thickness are taken into account.