LEAFLET NO. 39 MRH15

END JOINTS O4

SOUTHERN PINED. B. RICHARDS, ForesterB. M. COOL, Assistant Forester

I __,\ kIl Di1AY thlotSalid Oif0 SliOlt t )iCCCS

(dI solntherii Pille lII1fllbcl gil to waste

locacis there is no0 11,0ket for suchsizes. o tiie other ha, Ililost mnills

'Jo help Ilmbler(ini wsith this prol)1ci. thle Xgriciiltural F ' pei ncut Sta-tion of the Alalia PoIustechiii liistj-ttitu has been cond~ulctiug research ointhe pr oblem of lmakillg glued enld joilitslor souitherin pine.

The jo]in)1t prsted I i I cr showisss great

proinisc of reduucig muill ss istc byv mak-fig poissile the sallsage of short piecesof liuober. Ini addition, this joint can

hilp cexpand the onarkets lor soiithierin

p i hv alowiig tihe [productionl of

DESIGN 4/ NEW END JOINT

W\hile it is I tiatisl utis\c to (lue

b~oardfs together side INv sie or face toface and gyet stro ig joits. productioniof strong endi~ joinits hais alws bieen

dlifficuilt. Prclijljillai~ w sork oil sinflfeseai f joints has shiowsed that strong end1(

jolin ts call he miad(e iin siouth ern p iiic

lumb1 ier. Thiese silli pf scarf join ts, how-

ev er, w5aste hf ici. and~ doui not llidthenisels es to high piroduict ion, lowv-cost

mnethod((s oIf iiianl Ilturil. (O)n tihe otherihland. th eC ai e1 lojans t pCS of' fill(Tcc ( I

eod( jofints inll (se today~i thait can11 be

((lass fl (li e((f. llowscx ii the 1111 ll'

(liiin tx fpls full1 ishl little miore thainat thir o1(f tihe strcilgyth of clear wood

wshen hi (kill inl binfug. In a10 effor

to) colifiui tihe des1 iable sti eilgtl prop-

S T ATIO0NI N ST I TUTE

Auburn, Alabama

A G RIC U LT U RAL E XP ER I MEN To41Me ALABAMA POLYTECHNICF. V. Smith, Director

MARCH 1953

FIGURE 1 . The end joint, as viewed from the edge of a 1 -inch board. The dotted linesshow how the top and bottom truncations will be removed when dressed to 25 32 inch,leaving a 1 :6 scarf joint at each surface.

cti ox f thet scai joWint xN itl theC deir-able1 produ ction0 cb al dct( iticx of ithtb

fillgrld join t, a new\ typ of(i fingeredjoint wxas designedt( 1, Fig. I I.In a litam

Joint strength itkiln-dried lum-ber. In (Iiis xC o irii ic this uoint,

xxiwhc~~ ii boc tite centerI of a hcami

\\ili ix ragc lict\ te 75 andt 80) pert

tent of the sti (liil of' the( cleai xx 1)0.

[bt711 C i i.N(11y strtss (iC\co d (I jtt clf

I tijIIiC I 1130) pounids pi (liir

inch) is actiaii 4.7 tiniex areaiter tutuithe xxoiii stressi (xx 2401 ) ass xi ~i(eto) the betst xti (xx £'i idt of xlliii ii

Ipii1C. Ill x (.lkIr Sl)(C(i111Cil tilW \\ 51

FIGURE 2. Typical breaks in end-jointed southern pine when tested to destruction ina timber-testing machine. Due to slight brashness, the first two beams broke entirely inthe wood. Although the third beam broke partially along the joint, the rough nature ofthe break shows that the glue joint was strong enough to tear out pieces of wood.

will usually break without rupturingthe joint. Such breaks in the wood areshown in the first two beams in Figure2. Small square beams of this typegive approximately the same strengthregardless of whether the joint is placedflatwise or edgewise before breaking.As a demonstration of joint strength,Figure 8 shows a dressed 1 X 4 bentdown under the weight of three men.

Joint strength ia preservative-treated wood. Preservative-treatedwood that has had the excess solventremoved by the solvent-recovery processcan be satisfactorily end jointed withthis new joint. End joints in such wood 1

gave bending strengths nearly 80 percent as great as that of solid wood.

Since preservative-treated wood is de-signed to serve under extreme exposureconditions, the wet strength of anyglued joint is of great importance. Someof the treated beams were saturatedwith water and tested wet. Preliminaryresults show that with a good, water-proof glue very satisfactory wetstrengths are obtained.

METHODS j CUTTING dGLUING the JOINTS

The joints used in this study were cutwith a two-winged solid cutter mountedon a spindle shaper. The boards to bejointed were held in a simple woodenjig designed for this purpose. The jointswere cut by pushing the jig past thecutterhead with the edge of the jig heldagainst the shaper collar (title illustra-tion). No troublesome burning of thenarrow tips of the cutterhead has beenexperienced.

In production the joints could be cuton a single-end tenoner or on a flooringendmatcher with a glue spreading at-tachment. Since this joint is reversible,both halves of the joint can be cut onthe same cutterhead and the joint made

1 Copper-naphthenate treated lumber wasfurnished through courtesy of C. L. Briceof Brice Wood Preserving Corp., Archer,Fla.; and J. A. Greenwald of the CuprinolCo., Tampa, Fla.

to fit perfectly by turning one boardover and pushing it endwise against theother. For a moderate rate of produc-

tion, a single-end tenoner may be used.High speed production would requirea complete flooring endmatcher with aglue-spreading attachment on each ma-chine.

Strong joints have been obtained withresorcinol, phenolic, and urea type res-in glues. Most of the joints tested havebeen hot pressed. Preliminary results,however, indicate that satisfactory jointscan be made by curing the glue for asufficient length of time at normal roomtemperature. In either event, it is notnecessary to hold end pressure on thejoint. Once the joint has been forced to-gether endwise, it holds its position iftop pressure is applied with a press

having slightly roughened surfaces.This fact simplifies the design of pro-duction-type machinery to press and

cure the joint.

ERRORS l AVOID i DESIGNINGSIMILAR END JOINTS

It is believed that the present jointwill have many uses; however, a manu-facturer may want a joint that, althoughsimilar to this, is varied for some spe-cial purpose. In designing such joints,the common causes of weakness will beavoided by the following precautions:

1. Do not have a truncated tip at ornear the surface of the board. Thegreatest strength is obtained by havinga rather low-angle scarf extend to thesurface. If the joint is well glued, this

scarf will dress to a neat appearing joint;if poorly glued it will show a bad jointafter surfacing, and can be readily re-jected for uses requiring high strength.

2. Do not have broad tips on the fin-gers'. The 0.062 inch tips on this jointseem quite satisfactory. Rounded' tips0.080 inch wide have also been usedwith no great reduction in. strength.

8. Have as few truncated tips aspossible. The present arrangement ofthree scarfs and two truncated tipsseems to be the best combination for

\ill profalv lbe niecexssary to yo toi fixve

scaits ild( four tritittetti tips5 ill ordertol keep thle leingthi of tlic fingerIs dfoxwn

to at reasoniable figTi ii .-1. Doi liot Ilistext tlIiiX stee or e1 i2

trilll\ flalt scat Is. Piractical oji its wxith

'dii i-,tls fr om (65 to 85 per cciit of the1wititlwt sti tlwitli of, solid xxNood call bedes'igined wxithi seal I' slopes I hccii 1 :4

awyle of' 14 ) and 1:8 ( angle of 7.1Scat ts wxithi sflpes steepi thaii 1 :4sfiiixx lowx stretigtli \ alilts. l\(cfpt for\Ceiy speciid purposes. suich ats ttilai it

laiiililtioii. scarf's flatter thlii 1 :8 shouldhitax itled il jo fiiigyet joiolt. Flat scarf'srequnire either xvcry lol ig (i gyels, oi- iianvfitigrls inl hetice tliatix triiitetl tipsto serxe ' as poilits ()f xx tiktiess.

USES I,. END JOINTS

IThe first il mlost oliolts lOse of eiildjoints is to six age shor t pices of himl-bet bxv gTling themi into long( p~ieces.Also, lengyths eatl he ililde thait xx mildhlot he cotix enietit to sass oil the lsoll

saxx mill cai iagre. Fir exam ple. I '< 8bioard (lc011libe etild foil it(( to at leiig(tliof 2-1 f'eet mid thlci Litiittetl itnto 2

8 rafters 24 feet IonoPetrhaps the moist o*)loisilig, potssillil-

itx inl thle use of (11(1 joints is tit joinl

shoit boiards into iiiiig ones aind then

edge glue these long liiilods itito wxidepanlels iii :1 cotitios edige gluing-

press. Th fese pimcls, 2 or .3 feet xideZol pct flaps 24 feet loug. could hestocked 1x , v etatl x \ards atnid rtipped itnd(

Cross ci it to it ix sti thie customer mightxx atit. Such ai iiI I get~cilcilt wxould

gfrititx reduce thle illtixitii of ,i retiil

Yard. These pat els could allso sliisti-tite fl solic of the luses of p]x \x \\iitanld Scix c iti sotmle places xxherc pl -

xxiiofd is it iiici itte.

Thle pr octi it joif these linig xxidepiliels xx oild alsot iedcte the cost ofinaiiifactiii iligy cotnioletcitl liminlates o~fstiioilirtf forti. Foir examiple, fit fiitpalliels :3 feet xx\id]e coiuld he gluied itto

aitir ll*d hliitiatc f rilo xx hichllf fldoxsx wet the citrxed tnlctnflcts for l)oxx -

st'ii trutsses. lit the saii miltimer,enurxved 1bitrtil if tels c oild ble ma1iss P riduiccd lix glinit upxxide cursed latin-in itt's ili ( reis i ilg thl in to traftersx.

The fact thatpisrxtxc-hatlxxoiid cail ie hc iti sfa:ctoril lv enld jinited

opens tip) iicxs fields of itse. For example,trciteif x \oiii couild lit' Ii joitited anidedgye gFlutt itito xx ide piiex anid thlilililitted ilito licix% ai dies fur slip-pt ttig I hig txxax' atit ratili id bridgecs.Stich i x ii t et s trtuctiuires. of cinurse'xxiiili axc tiiil xx twod tlitomyighittil xxii1iltl bte 1) icticil iitutiie to rot

ori tetniftc (liiiizw.

FIGURE 3. An end-jointed 1 4 supporting 535 pounds over a 4-foot span. The1 -4 had been dressed to standard size (25 32"- 3-5 8'). It should be noted thatthere is an end joint between the feet of each man.