LEAFLET NO. 39 MRH15 END JOINTS O4 SOUTHERN PINE D. B. RICHARDS, Forester B. 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 such sizes. 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 oin the pr oblem of lmakillg glued enld joilits lor 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 pieces of 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 to face and gyet stro ig joits. productioni of strong endi~ joinits hais alws bieen dlifficuilt. Prclijljillai~ w sork oil sinflfe seai 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 llid thenisels es to high piroduict ion, lowv-cost mnethod((s oIf iiianl Ilturil. (O)n tihe otheri hland. 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 thain at 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 ATIO0N I N ST I TUTE Auburn, Alabama A G RIC U LT U RAL E XP ER I MEN T o41Me ALABAMA POLYTECHNIC F. V. Smith, Director MARCH 1953 FIGURE 1 . The end joint, as viewed from the edge of a 1 -inch board. The dotted lines show 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 fingered joint 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 tutui the xxoiii stressi (xx 2401 ) ass xi ~i(e to) 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 in a timber-testing machine. Due to slight brashness, the first two beams broke entirely in the wood. Although the third beam broke partially along the joint, the rough nature of the break shows that the glue joint was strong enough to tear out pieces of wood. will usually break without rupturing the joint. Such breaks in the wood are shown in the first two beams in Figure 2. Small square beams of this type give approximately the same strength regardless of whether the joint is placed flatwise or edgewise before breaking. As a demonstration of joint strength, Figure 8 shows a dressed 1 X 4 bent down under the weight of three men. Joint strength ia preservative- treated wood. Preservative-treated wood that has had the excess solvent removed by the solvent-recovery process can be satisfactorily end jointed with this new joint. End joints in such wood 1 gave bending strengths nearly 80 per cent as great as that of solid wood. Since preservative-treated wood is de- signed to serve under extreme exposure conditions, the wet strength of any glued joint is of great importance. Some of the treated beams were saturated with water and tested wet. Preliminary results show that with a good, water- proof glue very satisfactory wet strengths are obtained. METHODS j CUTTING d GLUING the JOINTS The joints used in this study were cut with a two-winged solid cutter mounted on a spindle shaper. The boards to be jointed were held in a simple wooden jig designed for this purpose. The joints were cut by pushing the jig past the cutterhead with the edge of the jig held against the shaper collar (title illustra- tion). No troublesome burning of the narrow tips of the cutterhead has been experienced. In production the joints could be cut on a single-end tenoner or on a flooring endmatcher with a glue spreading at- tachment. Since this joint is reversible, both halves of the joint can be cut on the same cutterhead and the joint made 1 Copper-naphthenate treated lumber was furnished through courtesy of C. L. Brice of Brice Wood Preserving Corp., Archer, Fla.; and J. A. Greenwald of the Cuprinol Co., Tampa, Fla. to fit perfectly by turning one board over and pushing it endwise against the other. For a moderate rate of produc- tion, a single-end tenoner may be used. High speed production would require a complete flooring endmatcher with a glue-spreading attachment on each ma- chine. Strong joints have been obtained with resorcinol, phenolic, and urea type res- in glues. Most of the joints tested have been hot pressed. Preliminary results, however, indicate that satisfactory joints can be made by curing the glue for a sufficient length of time at normal room temperature. In either event, it is not necessary to hold end pressure on the joint. Once the joint has been forced to- gether endwise, it holds its position if top 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 DESIGNING SIMILAR END JOINTS It is believed that the present joint will have many uses; however, a manu- facturer may want a joint that, although similar to this, is varied for some spe- cial purpose. In designing such joints, the common causes of weakness will be avoided by the following precautions: 1. Do not have a truncated tip at or near the surface of the board. The greatest strength is obtained by having a rather low-angle scarf extend to the surface. If the joint is well glued, this scarf will dress to a neat appearing joint; if poorly glued it will show a bad joint after 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 joint seem quite satisfactory. Rounded' tips 0.080 inch wide have also been used with no great reduction in . strength. 8. Have as few truncated tips as possible. The present arrangement of three scarfs and two truncated tips seems to be the best combination for \ill profalv lbe niecexssary to yo toi fixve scaits ild( four tritittetti tips5 ill order tol 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 the 1wititlwt sti tlwitli of, solid xxNood call be des'igined wxithi seal I' slopes I hccii 1 :4 awyle of' 14 ) and 1:8 ( angle of 7.1 Scat ts wxithi sflpes steepi thaii 1 :4 sfiiixx lowx stretigtli \ alilts. l\(cfpt for \Ceiy speciid purposes. suich ats ttilai it laiiililtioii. scarf's flatter thlii 1 :8 should hitax itled il jo fiiigyet joiolt. Flat scarf's requnire either xvcry lol ig (i gyels, oi- iianv fitigrls inl hetice tliatix triiitetl tips to serxe ' as poilits ()f xx tiktiess. USES I,. END JOINTS IThe first il mlost oliolts lOse of eiild joints is to six age shor t pices of himl- bet bxv gTling themi into long( p~ieces. Also, lengyths eatl he ililde thait xx mild hlot he cotix enietit to sass oil the lsoll saxx mill cai iagre. Fir exam ple. I '< 8 bioard (lc011libe etild foil it(( to at leiig(tli of 2-1 f'eet mid thlci Litiittetl itnto 2 8 rafters 24 feet Iono Petrhaps 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 wxide panlels iii :1 cotitios edige gluing- press. Th fese pimcls, 2 or .3 feet xide Zol pc t flaps 24 feet loug. could he stocked 1x , v etatl x \ards atnid rtipped itnd( Cross ci it to it ix sti thie customer might xx 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 \\iit anld Scix c iti sotmle places xxherc pl - xxiiofd is it iiici itte. Thle pr octi it joif these linig xxide piliels xx oild alsot iedcte the cost of inaiiifactiii iligy cotnioletcitl liminlates o~f stiioilirtf forti. Foir examiple, fit fiit palliels :3 feet xx\id]e coiuld he gluied itto aitir ll*d hliitiatc f rilo xx hichllf fldo xsx wet the citrxed tnlctnflcts for l)oxx - st'ii trutsses. lit the saii miltimer, enurxved 1bitrtil if tels c oild ble ma1iss P ri duiccd lix glinit upxxide cursed latin- in itt's ili ( reis i ilg thl in to traftersx. The fact thatpisrxtxc-hatl xxoiid cail ie hc iti sfa:ctoril lv enld jinited opens tip) iicxs fields of itse. For example, trciteif x \oiii couild lit' Ii joitited anid edgye gFlutt itito xx ide piiex anid thli lililitted 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 tlitomyighit til 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. The 1 -4 had been dressed to standard size (25 32"- 3-5 8'). It should be noted that there is an end joint between the feet of each man.