CARPENTRY. 





PLATE 

 CXXVI. 



Fig. 1. 



Fig. 2. 

 Fig. 3. 



?. 5. 



Fig. 6. 



Fig. 7. 



all the ribs : the concentric outer circle may be at 



any distance, . to tin- biv,i<!th of the nb, 



to m.ike it snilir;: -itly /"if A and 



e i X parallel t<> A i arc O 1< ai i: and i, 



and die outei edge at // anil X : draw / Q /', m n p o, 

 likew.se paiailel to AB ; and draw the section of the 

 kirl) O o n, then will Q p A A R f Q be the rib 

 required. lu the :,;mie manner may all the others be 

 found The ribs being found for one eighth part of 

 the o-ilin^i i sufficient lo mould the whole, as shown 

 at No. J, '2, ;i, -1, 



No. 1. is the rib that stand; in the diagonal. 



No. '2. the next succeeding on.-. 



No. :J. the rib succeeding No. 2. 



No. -k the middle rib of the side succeeding No. 2. 



OA is half the springing rib : the feet of the ceil- 

 ing are found by drawing lines from the ends of the 

 . of the ceiling-ribs on the side AD, perpendicu- 

 lar thereto, until they cut the top of the springing 

 rib. 



The springing ribs are here all of an equal radius, 

 and are portions of lesser circles of the sphere. 



To SCARF a beam, is to join two separate pieces of 

 timber, so that every superficies of the one piece shall 

 be respectively in the same plane with every super- 

 ficies of the other ; or, in common language, that 

 both pieces shall be in the same straight line, and 

 flush on all sides with each other. 



Hence it is evident, that if the joints consist of a 

 plane or planes at right angles to two opposite sides 

 of the beam, but not at right angles to the plane of 

 the other two opposite sides, the side of the one 

 piece of timber with which the oblique angles are 

 made, will form the same inclination or inclinations 

 respectively with the plane or planes of the joint, as 

 the opposite parallel side of the other piece will 

 make with the corresponding or coincident plane or 

 planes of the said joint. 



There are several methods of scarfing beams, either 

 by the joint consisting of one plane or several planes, 

 sometimes indented into each other. 



Fig. 1. shews the method of scarfing a beam by 

 indenting the joint at the ends, the planes of the joint 

 being both parallel and perpendicular to the planes of 

 two opposite sides. 



Fig. 2. is the method of scarfing a beam with the 

 coincident parts oblique to the two sides. 



Fig. 3. shews the method of scarfing a beam when 

 the joints are both parallel and perpendicular to the 

 two opposite sides, by being tabled and indented at 

 the ends, and keyed between the tables. 



Fig. 4. represents the method of scarfing a beam 

 with oblique and tabled joints, and keyed between the 

 tables. 



Fig. 5. exhibits the method of scarfing a beam with 

 parallel and perpendicular joints, oblique at the ends, 

 by forming the end of each piece into a series of steps. 



Fig. 6. shows the method of making a beam of 

 two pieces of timber, when the length of the two 

 parts are no more than the length required ; for the 

 whole, by inserting an intermediate piece on one side 

 of it each way, with a double series of steps. 



Fig. 7. shows the method of building a beam in 

 two thicknesses, having the parts of each half scarf- 



ed, as in Fig. 3. In this diagram, as well at in the 



four lir.t, the joints are strapped across at t! 

 lings, and bolted on each hide of the jun.t. The ^ 

 strapping is of great use in preventing the bolts 

 from sinking into the w> 



Fitf. 8. exhibits the method of building a beam in Pi-iTe 

 three thicknesses, as the ribs of a dome such a> the (; XXVI. 

 Halle du Bled, at Paris. Fl - 8 - 



NAKED FLOORING is the arrangement of the tinv w&td 

 bers to support the boarding. flooring. 



Floors are constructed by different methods, ac- 

 cording to the bearing of the timbers. When the 

 rooms liavc small dimensions, the floor generally con- 

 sists of single joints. When the rooms are large, the 

 floor consists of two rows of joists, the one support- 

 ing the other above, and framed at one end into a 

 large beam, called a Girder, which it generally dispo- 

 sed in the middle of the transverse dimension of the 

 space, if there are only two lengths of joisting, with 

 another compartment of joisting upon the other side of 

 it. If there are three compartments of jointing, there 

 will be two girders. The lower supporting row of 

 joists are called Binding Joists ; and the upper which 

 is supported is called Bridging Joists. The bridg- 

 ing joists are most frequently notched upon the bind- 

 ing joists, but not to the thickness of the binding 

 joists ; so that each edge of the upper side of the 

 binding joists are also notched, leaving the breadth 

 of the rising part equal to the breadth of the notches 

 in the under sides of the bridging joists. 



Fig. 9. represents naked flooring without binding Fig. 9, 

 joists, but with a girder, into which the joists that sup- 

 port the flooring are framed, and the ceiling joists into 

 deep joists which also support the boarding. No. Lisa 

 section shewing the end of the girder, and the ends of 

 the ceiling joists. No. 2. i a transverse section shew- 

 ing the ends of the boarding joists, the ends of the 

 strong joists, and the bides 01 the ceiling joists. 



Fig. 10. represents sections of a double floor. No. p; e j 



1. shows the ends of the girder, bridging joists and 

 ceiling joists, and the side of the binding touts. No. 



2. shows the ends of the binding joists, and the sides of 

 the bridging and ceiling joists. 



Truss Girders. 



When girders are extended beyond a certain length, Truss rd- 

 they become bent by their own weight, sagging down- er. 

 wards in the middle ; and the degree of curvature will 

 increase in a much greater degree than their lengths. 

 An excellent method to prevent the sagging, with- 

 out being supported by uprights, or posts from the 

 ground or floor below> is to make the beam in two 

 halves, and insert a truss so, that when the two halves 

 are bolted together, the truss may be between them. 

 In this truss, the two halves of the beam itself is the 

 tie of the truss. To prevent any bad effects from 

 the shrinking of the timber, the truss posts are gene- 

 rally constructed of iron, screwed and nutted at the 

 ends ; and, to give a firmer abutment at the ends, 

 the braces are let in with grooves into the side of 

 each half of the beam. The abutment at the ends 

 is also made of iron, and is either screwed and nut- 

 ted at each of the cads, and bolted through the 



