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Effects of Countersink Hole on Driving Torques of Screw in Joints Constructed of Medium Density Fiberboard

Aim of study: The aim of this study was to investigate the effect of countersink along with some other factors affecting screw driving torques in joints made of medium density fiberboard (MDF). There is limited research has been done in the field of screw driving torques in wood based composites. In all of these studies, the specimen consisted of a single wood-based composite material and metal plate which was used for the consistency of the screw driving data. However, in this study, the screw driving torques were obtained by the specimens consisted of two MDF testing blocks jointed by a screw. Material and Method: In general, there were two main screw driving torques; seating torque (SET) and stripping torque (STT). The MDF testing blocks had dimension of 150 mm long × 75 mm wide and two different thicknesses were used. For upper testing block, 8-mm-thick MDF and for lower testing block, 18-mm-thick MDF were used. Torques measurements were obtained by an adjustable torque screwdriver. Factors were embedded screw orientation (face-to-face and face-to-side), pilot-hole diameter (2.5 and 3.0 mm), pilot-hole depth (12 and 16 mm) and countersink type (with and without countersink). Main results: The results of statistical analysis indicated that the four-way interaction among the embedded screw orientation, screw length, countersink type and pilot-hole diameter was significant on the mean SET and STT in the MDF joints. Highlights: This study will help MDF manufacturers to understand the screw performance of their products in terms of screw driving torques.