/ 7 '7

CLINCHING Of NAILS IN CONTAINERCONSTRUCTION

March 1948

\143Rmii)

JAN 241951

No: 81777

UNITED STATES DEPARTMENT OF AGRICULTURE„FOREST SERVICE

LIOREST PRODUCTS LABORATORYMadison 5, Wisconsin

In Cooperation with the University of Wisconsin

CLINCHING OF NAILS IN CONTAINER CONSTRUCTION-

BY

E. H. BORKENHAGEN, Engineerand

H. J. KUELLING, Engineer

Forest Products Laboratory2 Forest ServiceU. S. Department of Agriculture

Summary

Clinching of nails has always been advocated by the U. S. Forest ProductsLaboratory as an accepted method of strengthening joints of wood boxes and crates,but nobody has ascertained just how much the joint strength was improved byclinching. Recent tests made at the Forest Products Laboratory are a steptoward clearing up this uncertainty. These tests show that single nails havefrom 45 to 464 percent more holding power when clinched than when unclinched,depending upon the state of dryness of the wood when they are driven and withdrawn. Nails clinched across the grain of the wood have about 20 percent greaterholding power than nails clinched with the grain.

Introduction

Among the many ideas advanced from time to time to improve the strength of join'of wood boxes and crates, clinching is probably the oldest and simplest. Clinch.ing has long been called for in certain phases of box and crate construction.Crate specifications require that, when the sheathing boards are fastened to theframe members and diagonals, the nails used shall be long enough to penetrateboth thicknesses of material and extend beyond 1/4 inch for clinching. Boxspecifications require the clinching of nails when fastening cleats to the endsof nailed wood boxes and when fastening cleats to the panels of cleated plywoodor cleated fiberboard boxes.

Recognizing the obvious fact that individual hand clinching is laborious, somemanufacturers devised methods that reduced this labor. In crate construction,a metal plate is used under the pieces being nailed together, with the nailsdriven at a slight angle so that the nail points, upon emergence from the wood,

1-Published in Shipping Management, March, 1948.2Maintained at Madison 5, Wis., in cooperation with the University of

Wisconsin.

Report No. R1777 -1- Agriculture-Madison

strike the plate and are bent into a clinch. In box construction, nailingmachines are usually used in the nailing operations and most of these machinesare equipped with automatic clinching bars for that purpose.

As a basis for evaluating the true efficiency of clinched versus unclinchednails, the U. S. Forest Products Laboratory has conducted tests of single nailsdriven into and through two pieces of wood. These tests demonstrated that,under the conditions studied:

(1) Clinched nails had from 56 to 161 percent more holding power thanunclinched nails when driven into and pulled immediately from air-seasoned lumber (moisture content about 11 percent).

(2) Clinched nails had from 45 to 173 percent more holding power than un-clinched nails when driven into and pulled immediately from partiallydry lumber (moisture content about-22 percent).

(3) Clinched nails had from 250 to 464 percent more holding power than un-clinched nails when driven into partially dry lumber which was permitted.to dry to about 11 percent moisture content before the nails were pulled.,

(4) Nails clinched across the grain had approximately 20 percent moreresistance to withdrawal than nails clinched with the grain.

For practical purposes, these results showed, that the clinching of nails improvesthe strength of the joint practically the same amount when the nails were driveninto and pulled immediately from air-seasoned or partially dry lumber. Thegreatest increase in joint strength occurred in partially dry wood that wassubsequently kiln-dried to air-seasoned condition before the nails were pulled.This is a common enough occurrence when boxes or cPates are made of unseasonedlumber and allowed to stand around before being used. It should not be assumed,however, that such improvement in joint strength justifies the use of greenlumber for box and crate construction, because it is not possible to clinch allof the nails used in the assembly of boxes and crates. In the nailing of sides,top and bottom to ends and cleats in box construction and in the nailing ofends and sides to the base or tops to the ends and sides in crate construction,it is impossible to clinch the nails. Since this assembly nailing is animportant factor in determining the strength of these containers, the require-ments specifying the use of: dry lumber, which give the best result, should notbe waived. Since thtse tests were conducted with single nails driven throughtwo pieces of wood, such effects of drying as warping, twisting, and splittingof lumber in a box or crate are not evaluated.

The following discussion presents the basic test data upon which these general,conclusions are based.

Description of Material

Two sets of static withdrawal tests were conducted, the first set with Douglas-fir under three different moisture conditions, and the second with three speciesof wood (Eastern white pine, Southern yellow pine, and Douglas-fir) in the

Report No. R1777 -2-

air-seasoned condition. The tests were made on wood with moisture content attime of test as follows:

Average moisture contentat time of test

(Percent)

Kiln-dried Douglas-fir 10Partially dry Douglas-fir 22Partially dry :Douglas-fir nailed at 22 percent

and kiln-dried for 8 days 11Air-seasoned Eastern-white pine, Southernyellow pine, and Douglas-fir 11

.The type of test specimen used for these'tests is shown in figure 1. Eachtest specimen contained three nails of one size and kind driven through a 3/4-inch thick face plate (block A of Fig. 1) and into either_another 3/4-inch or1-5/8-inch block (bioCk . 114jf Fig. 1), the thickness of the second block depend-ing upon the length of the nail. For the tests of unclinched nails, the nailswere driven through both blocks of wood with the points left protruding in theinstances where the length of the nail exceeded the total thickness of the twoblock8:: For clinched nails, the nails were driven through both blocks of woodand clinched individually with a hammer, some across the grain of the wood andsome With the.grain. All nails were driven perpendicular to the surface of theblock and spaced as shown in figure 1. The sizes and types of nails tested arelisted in table 1.

Fifteen nails of each size, type, and clinching condition were tested inDouglas-fir at each of the three moisture conditions, and in each of the threespecies, Eastern white pine, Southern yellow pine, and Douglas-fir, in theair-seasoned condition.

Method of Testing

In the first set of tests, using only Douglas-fir wood blocks, nails weredriven into kiln-dried wood and pulled immediately; driven into partiallydried wood and pulled immediately; and driven into partially dried wood whichwas kiln-dried to 11 percent before the nails were pulled. In the second setof tests, the nails were driven into and pulled immediately from Eastern whitepine, Southern yellow pine, and Douglas-fir, all in the air-seasoned condition.

Immediately before testing, the top block of wood in each specimen (block A,Fig. 1) was split off around the nails to make it possible to pull each nailindividually. The nails were pulled at a speed of 0.1802 inch per minute bymeans of asTecial gripping device used in connection with a universal testingmachine (Fig 2). Load was . aPplied until the nail pulled out. Maximum load,which usually occurred when the nail pulled only a fraction of an inch, isrecorded in tables 2 and 3.

Report No. R1777

Effect of Moisture Condition on Strength of Joint

The present tests,are in accord with previous studies made at the ForestProducts Laboratory, which show that unclinched nails lose much of their resis-tance to withdrawal when driven into partially dried wood which is subsequentlydried further before the nails are pulled. These tests showed that the averagewithdrawal load of the five sizes of unclinched nails, driven into partiallydried wood which was then kiln-dried before they were 0.119d.was about 59 percentlower than that obtained from those driven into and pulled immediately fromkiln-dried wood; and 57 percent Tower than obtained fro those driven into andpulled immediately from partially dried wood. Then the nails were clinched,however, there was no significant difference between the withdrawal loads underthe three moisture Conditions (table ,4).

Comparisons of Clinched and UnClincheOlails of the Same Size

The importance of clinching is further demonstrated by comparisons of the with-drawal loads required to pull the same sizes of nails, 4inc4ed and unclinched.The results in table . 2 show that, for nails driven into dry lumber and pulle once, the sixpenny clinched pright_box . nails required 42 percent greater with-

drawal loads than the unclinched sixpenny cement-coated , sinker nails; whendriven into partially dried wood and pulled at once the clinched bright box nailsrequired 101 percent greater withdrawal loads; and when driven into partiallydried wood which to 11 percent before pulling the nails, theclinched bright box nails required 250 percent greater withdrawal loads. Thesixpenny clinched common nails required 75 percent, 175 percent, and 350 percentgreater withdrawal loads, respectively, than the sixpenny cement-coated nailsunder the above conditions of moisture content.

In these comparisons, some cognizance should be given to the fact that the brightbox and common nails have a greater-Shank - diameter than the sinker nail; hence,some increase in the withdrawal loads would be expected. The comparison has apractical significance, however, inasmuch as box and crate specifications requirecement-coated nails where no clinch is made, but bright nails are'permittedwhere they are clinched. Therefore, in practice, a sixpenny bright box or commonnail might be used where clinching is specified, whereas a sixpenicement-coated sinker might be used where clinching is not specified.

The clinched tenpenny common nails required 106 Percent, 45 percent, and.464 percent greater withdrawal loads, respectively, than the unclinched tenpennynails under the three moisture conditions,

Clinching of Naii.- P With and across the Grain of the Wood"

The tests of the three kinds of nails which were clinched"with or across thegrain showed that clinching of the nails across the grain resulted in withdrawalloads approximately 20 percent greater than clinching with the grain. Theresults are tabulated in table 5.

Report No. R1777 -4-

Table 1.--Sizes and types of nails tested

Size of :

Type of nail

Tested undernail : following conditions

Fivepenny : Cement-coated sinker : Not clinched

Sixpenny : Cement-coated sinker : Not clinched

: Cement-coated sinker :

: Cement-coated sinker :

Sixpenny :

Sixpenny

Sixpenny :

Sixpenny

Eightpenny

Ninepenny

Tenpenny : Bright common

Tenpenny : Bright common

Tenpenny : Bright common

: Clinched across grain

: Clinched with grain

: Clinched across grain

: Clinched with grain

Not clinched

Not clinched

Not clinched

: Clinched across grain

: Clinched with grain

Bright common

: Bright common

Bright box

: Bright box

Report No: 81777

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Table 4.--Average withdrawal loads, showing effect ofmoisture conditions on clinched andunclenched nails in Douglas-fir

Test condition : Average : Relation to: withdrawal :"driven-dry,: load : pulled-dry"

Unclinched nails (average of5d, 6d, 8d, 9d, and 10dnails)

::

Pounds

:

:

::

load

Percent

• 1

Driven dry--pulled dry • 179 : 100

Driven partially dry-- •. :

pulled partially dry • 171 : 95

Driven partially dry-- : :pulled dry • 74 : 41

Clinched nails (average of6d and 10d nails clinched : :both ways) •. :

Driven dry—pulled dry • 270 : 100

Driven partially dry-- : :pulled partially dry • 278 : 103

Driven partially dry-- : :pulled dry .. 1 • 296 : 110

Report No. R1777

Table --Average withdrawal loads of nails clinchedwith the grain and across the grain

Type of nail and test condition•

t Average withdrawal : Relation ofload : cross-grain to

with-grain: Clinched : Clinched : clinch: with : across :

grain : grain :

Pounds : Pounds : Percent

• Tests made in Douglas-fir under various moisture conditions

Sixpenny bright box nails •. :Driven dry--pulled dry • 149 : 155 : 104

Driven partially dry--pulled partially dry :: 132137 : 181Driven partially dry--pulled dry : 126145 : 183

AVERAGE • • 121:

Sixpenny common nail : : :Driven dry--pulled dry • 174 : 199 : 114Driven partially dry--pulled partially dry : 179 : 254 : 142Driven partially dry--pulled dry • 187 : 235 : 126

AVERAGE • • • 127

Tenpenny common nail : : :Driven dry--pulled dry •117Driven partially dry--pulled partially dry :

435 : 510 :396 : 524 : 132

Driven partially dry--pulled dry • 437 : 589 : 135AVERAGE • • 128

Tests made in three species - all air-seasoned

Sixpenny bright box nail Eastern white pine • 120 : 143 : 119Southern yellow pine • 144 : 182 : 126Douglas-fir • 206 : 217 : 105

AVERAGE • • 117

Sixpenny common nail : : :Eastern white pine - 126 : 165 : 131Southern yellow pine 185 : 215 : 116Douglas-fir • 250 : 298 : 119

AVERAGE • • • 122

Tenpenny common nail : : .Eastern white pine • 293 : 368 126Southern yellow pine 357 : 425 : 119Douglas-fir • •

AVERAGE 122

Report No. 81777

ZM 7:,5733. P„

Figure -Test specimen for making direct withdrawn]. testsof nails.

Report No, Rl777

ZM 11535 F

Figure 2.--Special gripping device used on the universaltesting machine for making direct nail with-drawal tests.

Report No. 81777

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