During lumber rolling, a fixation device is typically installed just behind the work roll to set up the delivery thickness and to fix the thickness reduction. However, the accompanying resistance force into the fixation device can cause slippage between the roll and material, indicating a bound for the rolling conditions. Slippage can be avoided by decreasing the resistance force or by adding a pushing force on the lumber from the entry side of the rolling mill. This paper experimentally investigated the effects of these horizontal forces on the rolling force and roll torque. From these results, the roll torque was found to be directly affected by the horizontal forces, but the rolling force was not affected. Secondly, a new parameter μeq was introduced and a condition of non-slippage, in which μeq must be less than the coefficient of static friction to avoid slippage, was proposed. This condition was then used to predict and to protect against slippage by identifying when this condition was violated and then applying a horizontal force to decrease μeq.