Relationship Between Driving Torque and Screwholding Strength in Particleboard and Plywood

Studies were made of the effect produced on withdrawal strength by overdriving screws. The results confirmed the difficulty of power-driving screws into particleboard and softwood plywood. The governing characteristic is the small difference between the torque required to set the screw flush and the torque that will overdrive the screw and damage the withdrawal strength. The reputation that particleboard has acquired for low screwholding capability may in some measure result from screws being overdriven to the point at which the potential screwholding strength of the board is only partially realized. The torque measurement provides a means of determining the extent of such overdriving. The torque wrench can be used to turn a previously inserted screw a quarter to a half turn in order to measure the torque resistance. If the torque is low and does not tend to increase, the screw has been badly overdriven and the withdrawal strength will be low.

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