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### Screws Fastener in Particle Board Maximum Torque and Pullout Withdraw Resistance Force Formulae and Calc

Screws Fastener in Particle Board Maximum Torque and Pullout Withdraw Resistance Force Formulae and Calculator

Tapping screws are commonly used in particle board where withdrawal strength is important. Care must be taken when tightening screws in particle board to avoid stripping the threads.

The maximum amount of torque that can be applied to a screw before the threads in the particle board are stripped is given by:

T = 3.16 + 0.0096 X (Metric, SI Units),

T = 27.98 + 1.36 X (Inch Lb Units).

A modest tightening of screws in many cases provides an effective compromise between optimizing withdrawal resistance and stripping threads.

Where:

T = Torque (N–m, in–lb)
X = Density of the particle board (kg/m3, lb/ft3).

Example: For 8-gauge screws with a depth of penetration of 15.9 mm (5/8 in.). The maximum torque is fairly constant for lead holes of 0 to 90% of the root diameter of the screw.

Ultimate withdrawal loads P (N, lb) of screws from particle board can be predicted by

P = K D(1/2) ( L - D/3 )(5/4) G2

Applies when the setting torque is between 60% to 90% of T

Where:

P = Ultimate withdrawal load (N, lb),
G = Specific gravity based on oven dry weight and volume at 12% moisture content,
D = shank diameter of the screw (mm, in.),
L = Length of penetration of the threaded part of the screw (mm, in.).
K = Constant 41.1 for withdrawal from the face of the board; for metric SI units,
K = Constant 31.8 for withdrawal from the edge; for metric SI units,
K = Constant 2,655 for withdrawal from the face of the board; inch–pound measurements
K = Constant 2,055 for withdrawal from the edge; for inch–pound measurements.

This equation can also predict the withdrawal of screws from fiberboard with K = 57.3 (metric) or 3,700 (inch– pound) for the face and K = 44.3 (metric) or 2,860 (inch– pound) for the edge of the board.

Withdrawal resistance of screws from particle board is not significantly different for lead holes of 50% to 90% of the root diameter. A higher setting torque will produce a somewhat higher withdrawal load, but there is only a slight difference (3%) in values between 60% to 90% setting torques

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References:

• AF&PA. 1997. National design specification for wood construction. Washington, DC: American Forest & Paper Association.
• ASCE. 1995. Standard for load and resistance factor design (LRFD) for engineered wood construction. Washington, DC:
• American Society of Civil Engineers. ASCE. 1996. Mechanical connections in wood structures. Washington, DC: American Society of Civil Engineers.