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Parts be' ' scar ^ consisting of six steps, the abuttingsmall dg ln ^ ec l u al, and the longitudinal parts inclined in ato be bolT j 6 to t ' le sides ; so that when the two parts comethereby 6< * to S et her, the pieces will dovetail each other, andto 8 hrint r,eVent t ^ le * r being drawn ; but as all timber is liable

dei

he so ace can he put in dovetailing, for the shrinking maymerit 0 ^ 1 ’ t h at the thickest parts of the solids at the abut-a nd ren , " e joint may pass through the narrower cavities,the Case e , r the dovetails useless. We may also observe, infrom ea j bolting, that when the longitudinal parts shrinkthe tr ail g 1 °ther, the bolts will be drawn obliquely, unless?Pposite t' 61 '^ 6 P arts on the sides be stripped and bolted, both/he strength 6 scarf and through the solid at each end of it.hy th e i r the compound beam may likewise be assisted

at fresi otl n ’ ^' e dovetailing therefore can only give greater°h stren,,^ 1 ^ rs t» at the same time, it occasions a small loss0(lter sten Ct t Ua ^ t0 the difference of the extreme end of the^%«re > » an i t ^ e nearer el, d of the whole section.

"'hen the " , e Dlet hod of forming a compound timber,h° ^ a P> bv W ° P' eces are not sufficient length to allow themt mubl e sca 1 f eans a third piece, connected with both by a. at titig u ’ fr )riMe d of several degrees, or steps; the piecesP |e ce 0V P?* ea ch other, witli the middle of the connecting, ^ r h en "■ tl ' eir abutment.

f Q d Unde ) r . s aie ext ended beyond a certain length, they] CUrv atnr * . r , own weight in the middle, and the degree6n 8ths. , e w, h increase in a much greater degree than theirthe aa - n exce hent method to prevent this sagging, with-j ° 0r bel 0 \ v Slatance °f u P r 'ghts or posts from tiie ground ortf 8ert a tl .’ Is ’ to uiake the beam in two equal lengths, and’p Usa may r SS ’. S0 that, when the two pieces are bolted, thea ° Preve^ 6 lnt ^ u d®d between them, they forming its tie.®gener a ii an 7 had effects from shrinking, the truss-posts8 ’ and t C0 . nstru cted of iron, screwed and nutted at the‘a gr 00 y„ 0 .S lve a firmer abutment, the braces are let inat e et >d a are S lnto the side of each flitch. The abutments atbj 6ac h of tt, S0 m& de of iron, and either screwed and nuttedwith 6 v n ^ 3 ’ an< i bolted through the thickness of bothab Ut y P°n th ° r ° a< ^ P art i rl the middle, that the braces mayt^ patents a 6 w hole dimension of their section ; or, the6 «r e y tt( “Uband™^ 6 in . the form of an inverted wedge attyj^ed an’jj n< * r * se cylindrically to the top, where they arethj * °ne kin^'u te ^‘. These modes may be either constructedh 0 j, a of th e j a °fr in the middle, or with a truss-bolt at one-8 ’ they • e . n £th from each end. When there are twtic^aaaces in a C . e a straining place in the middle.

Aa ’ fr'e j att J eit her be constructed of oak, or cast or wroughtbett' V °°d cont*^ mater iai is, however, very seldom employed.th e 8r for th e racts i ess in length than most metals, oak isfrorr°''. e UiUst v Ur P° se than cast iron, but then the parts ofthe ]'/ i n dispe n @ m muc ^ stronger. As to the bolts, wroughts will .. a ble. It is nhvimna tliat the hicrher the pbrder.

ln proportion to the dimensions of its section, no

two

The

‘ess

It is obvious, that the higher the girder,

' 8 "'’ll th 11IS °b vl °us, that theke av v there vi]P arts affected by the stress, and conse-pj "^sht. 11 i ess risk of their giving way under‘he 9 a ^ thr ongh long bearings.

of two thicknesses bolted together,

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l bi ( .

^ '^Uesseg PaCa i eil gth of timber alternating in thehie ® °Ue 80 as to have the junction of two lengthsfigure • thi e h nesa °PP os ‘ te th® centre of a length in

ess:

oppositethe scarfing

length

• - -to otamnK is similar to that of

10. A , 8

• ?Pus C ^ n ®ss e ea . ni °P l bree thicknesses bolted together,i°iuts ; tl ’ .tliat ti, 0118 ’ 8 . 1 ' 11 ® °f a number of short timbers so6v ery t ®frher 0 fI^ts in no thickness come opposite the^joints. 116 ot ^ er thicknesses j a bolt occurs between

Figure 11. A section of a girder with two braces anda king-bolt.

Figure 12. The section of a girder with a straining piece,two braces, and two truss-bolts, of the best principle. No. 1,represents the girder laid open, in order to show the core.No. 2, the two parts bolted together. No. 3, the edge of awasher. No. 4, the face of the same. No. 5, the side of thecut metal bolts, in the transverse direction of the girder.No. 6, the side of the same, in the longitudinal direction.No. 7, the transverse direction of the truss-bolt, or king-bolt.

Figure 13. The section of a girder, calculated from itsrise to sustain very heavy weights. If the tie-beam be verystrong, the abutments may be wedged ; but then the wedgesought to be very long, the tapper very small, that there maybe no inclination to rise. The excess of length may be cutoff afterwards. The bolts represented at No. 5, and No. 6,Figure 12, are nevertheless to be preferred.

Two timbers may be joined, either by making both planesof contact parallel with or at right angles to the fibres, or bymaking the joint parallel with the fibres of the one piece, andat right or oblique angles to those of the other, or at obliqueangles to the fibres of both pieces. When two pieces oftimber are joined so that the common seam runs parallel withthe fibres of both, the joint is called a longitudinal joint; butwhen the plane of the joint is at right angles to the fibres, itis an abutting, or butt-joint; this position brings the fibresof both pieces in the same straight line. If the joint be atright angles to the fibres of one piece, and parallel with thoseof the other, it is called a square joint; if the joint be parallelwith the fibres of one piece and oblique to those of the other,it is a bevel joint; and lastly, if the joint be at oblique angleswith the fibres of both pieces, the fibres forming an anglewith each other double to that formed by the fibres of onepiece and the joint, it is a mitre joint.

These are the general positions of simple joints in respectto the fibres of one or both pieces; those which may be com-pounded by the position of different planes, are of infinitevariety, but as they seem to have little or no practical appli-cation, we shall not detain the reader longer on the subject.

In fixing two pieces of timber together with longitudinaljoints, the pieces are generally bolted, and sometimes pinned.

As to butting and mitre joints, they are seldom or neverused in carpentry.

When two pieces of timber are joined together at one ormore angles, the one piece will either meet the other and formone angle, or by crossing it form two angles ; or the twotimbers will cross each other, and form four angles.

In all the following cases of connecting two timbers, it issupposed that the sides of the pieces are parallel with thefibres, or, if the fibres be crooked, as nearly so as possible ;and that each piece has at least one of its surfaces in thesame plane with those of one of the other ; the four sidesbeing at right angles to each other.

The angle or angles so formed will either be right or obtuse. !Notching is the most common and simple form, in permanent ;works, and in some cases the strongest, for joining two tim- |bers at one or more angles, particularly when bolted at thejoint. The form of the joint may be varied according to the !position of the sides of the pieces, the number of angles, !the quantity and direction of the stress on the one or both jpieces, or any combination of these circumstances.

In the notching of timbers upon each other, the notch isgenerally supposed to be formed by planes, at right anglesto, and parallel with the side in which the excavation is made;therefore the part of the corresponding piece must have itsplanes in a similar situation, the solid being contained betweenthese planes, instead of the empty space, or notch, as in the