Related Resources: Civil Engineering

Holding Power of Wood Screws

Civil Engineering and Design
Engineering Fasteners Design and Engineering

Holding Power of Wood Screws
Bureau of Standards
I.J. Fairchild
Technologic Papers of the Bureau Standards
34 pages

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Open: Holding Power of Wood Screws

Abstract:

The results of tests of the holding power of over 10,000 wood screws inserted in the side and end grain of seven kinds of wood, viz, yellow poplar, cypress, sycamore, North Carolina pine, Georgia pine, hard maple, and white oak, are tabulated and discussed. The effect of various sizes of lead holes, of screw lubrication, of cracks in the wood, and of the dimensions and finish of the screws is described.

Introduction:

This investigation was undertaken in response to specific requests for data on the holding power of wood screws in the application of builders' hardware, and for the benefit of manufacturers of furniture, fixtures, vehicles, freight cars, ships, pianos, woodenware, boxes and crates, and other users of wood screws.

" Holding power" is here defined as the maximum load in tension which a given screw can withstand when the load is applied to the head of the screw along its axis. The load may reach its maximum limit either (a) through the withdrawal of the screw from the wood,
or (Jo) in the denser woods through the breaking of the screw by fracture at the root of a thread near the shank, or (c) by collapse of the head of the screw.

Since over 80 per cent of the wood screws manufactured are of steel with flat head, the tests were confined to this type. Ninetyfive sizes were used, including every standard diameter from the smallest to the largest, in one-half of all the standard lengths. Seven different kinds of wood were employed, covering the full range of densities from the softest to the hardest woods in common use, in order to obtain the complete range of maximum direct tensional loads which wood screws are capable of supporting.

TOC

I. Introduction 553
1. Scope of the tests 553
2. Previous investigations 554
3. Acknowledgments 554

II. Description of materials used 555
1. Wood screws 555
2. Timbers 555
3. Presentation of screw to grain of wood 557

III. Apparatus for tests 558
1. Testing machine 558
2. Special equipment 560

IV. Method, results, and discussion of the tests 561
1. Lead-hole size 561
2. Lubrication 565
3. Side grain 566
4. End grain 577
5. Screw design 578

V. General summary 579

VI. Bibliography 580