CON

196

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other. It may also here be remarked, that the notch isgenerally supposed to consist of three planes, unless it beotherwise specified.

Notching admits of the two pieces being joined at fromone to four angles ; but joining by mortise and tenon admitscnly from one to two angles.

In mortise and tenon joining, four sides of the mortise arealways supposed to be at right angles to each other and tothe surface whence it is recessed, and two of these sides to beparallel with each of the sides, which form a right angle withthe side from which the mortise is made ; the fifth plane,which is the bottom of the mortise, is parallel with the other,j With respect to the tenon, four of its sides are parallel with! the four sides of the piece.

In the application of timbers to buildings, it is here sup-posed that all pieces cut for use have a rectangular section,and when laid horizontally have their sides perpendicular to,and parallel with, the horizon.

If two pieces of timber are to be joined at four angles, cuta notch in one piece equal to the breadth of the other, so asto leave the remaining part of the thickness sufficiently strong,a very small excavation being sufficient; then insert the otherpiece in the notch r or if the work be required to be veryfirm, notch each piece reciprocally to each other's breadth,

! and fasten them together by pins, spikes, or bolts, as the casei may require : this form is applicable where the pieces areequally exposed to a strain.

| When one piece has to sustain another over it, transversely,

1 and if only the upper be required to support a weight, cuta notch from its lower side, equal in breadth to about three-i fourths of that of the lower piece, and as deep as the vertical| distance that it is to be let down ; then the lower piece mustj have a notch cut in its vertical side, leaving the middle ofthe upper face entire to three-quarters of its breadth, andthe lower parts of the vertical side entire, so that the verticaldepth of each notch may be the same as that of the uppernotch : by this means the strength of the supporting or lowerpieces is diminished in a much less degree than if the notchwere cut out the whole breadth. This method is applicableto roofing and naked flooring.

The framing of timber by dovetail notching is chieflyapplicable to horizontal framing, where the lower timber issufficiently supported ; but where the lower timber is unsup-ported, it is common to use mortise and tenon, which doesnot weaken the timber in any considerable degree; wherethe timber is notched from the upper side, the operationreduces its thickness, and consequently impairs its strengtli ;though it may be said, if the solid of one piece fill the exca-vation of the other, and both be tightly driven or forcedtogether (if we can place implicit confidence in the experi-ments of Du Ilamel) and if the pieces be not cut more thanone-third through, there will be rather an accession thana loss of strength. It may be observed, however, that inlarge works, where heavy timbers are employed, it is difficult,or almost impossible, to fit them with due accuracy; and evenwhere the joints closely fitted at first, the shrinking wouldoccasion cavities on the sides, that would render the tenonsof no avail, because the axis of fracture would be nearer tothe breaking, or under side of the supporting piece.

What has been observed with regard to horizontal piecesof timber, applies to framing in every position, where theforce is to fall on the plane of the sides; and if a number ofpieces thus liable to lateral pressure on either side, are to beframed into two other stiff pieces, the mortise and tenon willprove best for the purpose.

When joists are framed into trimmers, the usual methodis to make the mortise on the tenon with a plain shoulder, in

the middle of the sides of its respective timber: this 111

me miuuKj ui uiu aiuca l/l us ico^cviuvo m»u«v - ^

is particularly used in letting down bridging joistsbinding joists, and small rafters upon purlins.

If it be required to join two pieces of timber, to tor j gright angles, so as to be immovable when the tn ) nsVf jj; r ec*held or fixed fast, and the standing piece pulled in a ^ 0 flion of its length ; cut a dovetail notch across the -br® of ti. etiie transverse piece, and notcli out the vertical sides 0 . D gstanding piece at the end, so as to form a corresp ® 1 ^ jCsimilar and equal solid. In some pieces of work, be=> ' ,j el -dovetail, an additional notch is cut, to receive the s'of the lower piece. If the position of these pieces ezontal, and the upper of sufficient weight, or presse ^by any considerable force, when the pieces are put f j l0 utin their place, the dovetail will be sufficiently strong ' .j 0 nthe assistance of pins, spikes, or bolts. This cons r t |,erequires the timbers to be well seasoned, for otliei' vshrinking will permit the standing piece to be drawn c0 „.the transverse, and thus defeat the purpose which 0 fstruction was intended to answer. The following me flieremedying this, defect will be found effectual: ■ sotransverse piece in two excavations from the upp e f e qii: 1 'that if the breadth be supposed to be divided into fa Iut ne*‘parts, and a notch equal in breadth to three parts be ^ ull l

to the outer vertical side, and the other notch be nia t |iii

7 _ .1

from

iece,

so

to

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to the breadth of one part, and each notch depressedupper face about one-third the thickness of the P 1to leave the second part on the upper surface ne-inner vertical side, and the two-thirds of the de Pw,vertical side next to the lower side entire: then tn ^ tli«ponding single notch being made on the standing P ie t "' 0solid left on the upper surface of the transverse p iece ’pieces will reciprocally receive each other. . y lifff 6

When binding joints are framed into girders, as Jto support the bridging joists and boarding of the n ’ 0 l -de Jwill be a considerable strain at their extremities j ^to make the tenons sufficiently strong to resistthey should be framed with a shorter bearing teno c! ille°to the principal tenon and a sloping shoulder noa tusk ; tenons thus formed are called tush tenons- ^ ha v ®When two parallel pieces, quite immovable, a 1 ,^_JnS elanother piece framed between them, proceed thus ^ g jiathe one end of the tenon of the connecting piece 1 g ;delow mortise, and make a long mortise in the opp° iiW v,e . tthe other timber, so that when the cross pie° e cel) ti'C!round the shoulder of the other extremity, a 3 a ()[1 ; it tl1 ^may slide home to its situation: thus if the ten ^movable end fit the mortise closely, the bottomtise would be the arc of a circle, of which the^ ^ bo tt0 0 .

the tenon first formed would be the centre :

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of the long mortise may be straight instead of cl * C t j ](3 pie c ^vided it be sufficiently recessed to clear the end 0This mode of framing a transverse piece between j 0 iS^is employed in trimming in ceiling joists: the k 1 ”. 0 ged Jare always previously mortised before they are * ge ldo ^a situation to receive them, and the ceiling jm ®* 3 bail* 1 *or never cut to their lengths and fitted in beforeis covered over. q be tv

When a transverse piece of timber is to be P'®. 111 ® are 11two parallel joists, of which the vertical surface^parallel, turn the upper edge of the transverse P.^.wards upon the upper horizontal surface of the J g(jr faC ethe interval or distance between them upon t e iTa {iS* et ^ ethe transverse piece now under; then turn ’tn® , aC ing typiece in the way it is intended to be framed) P^ appj 0edge over the places where it is to be let down > s 1a straight-edge to the oblique surface of the J° lS