Impact of Drill Bit Wear on Screw Withdrawal Resistance in Pinewood

Many factors affect screw withdrawal resistance (SWR), including screw size, embedment depth, the pre-drilled hole's diameter, dimensional accuracy, and the furniture pieces' material properties being joined. While prior research has extensively examined the influence of these factors, this study aimed to explore a neglected factor: how drill bit wear impacts pilot hole quality and subsequent SWR. The experimental setup included pinewood samples with pre-drilled 5 mm diameter blind pilot holes with a depth of 45 mm. The holes were equally divided into two groups: one drilled with a sharp bit, the other with a blunt bit. Euro-type coarse furniture screws (7 mm major diameter, 4 mm minor diameter, 3 mm pitch) were screwed into all holes. Subsequently, SWR was measured using a universal testing machine. Results show a statistically significant decrease in SWR when using the blunt drill bit. This phenomenon can be explained by excessive local material degradation, increased surface roughness, and disrupted hole dimensional accuracy, collectively hindering SWR. The study's findings offer insights into how excessive drill bit wear impacts the screw withdrawal capacity of pinewood, informing best practices in furniture and construction.