538 



CARPENTRY. 



Carpentry. 



Fig. 10. 



Construe- inner or second abutment ; both these abutments be- 

 tive j n g at r ight angles to the rafter. 



Fig. 8. represents another method of securing the 

 j^T^T" ' rafters and tie beam. No. 1 . The two joined together. 

 CXXVIII. No. 2. The end of the beam showing the socket. 

 Fig. 8. Fig. 9. shews the method of joining the struts and 



*% 9 ' king post when there is a deficiency of wood at the 

 joggles. Tliis also shows the method of forming the 

 dovetail on the tenon which goes into the beam. 



Fig. 10. shews the method of joining the wall plate 

 at the angles. No. l.The horizontal projection, show- 

 ing the diagonal tie and dragon piece which contains 

 the socket for the feet of the principal rafters. No. 

 2. The elevation of the high rafter framed into the 

 dragon piece. No. 3. Shows one side of the wall 

 plate with the sockets. 



As all timber will shrink unless it has been season- 

 ed for a considerable time, and, as the time which it 

 requires to season must depend greatly on the thick- 

 ness of the timber ; so the timber in all large roofs, 

 constructed with king posts and queen posts, will also 

 shrink ; and as the timber is large, the time required 

 must be very long, and perhaps even then not to be 

 depended upon. It has been found, that roofs have 

 sustained very considerable injury by the shrinking 

 of the timbers, in causing them to sag and press 

 down the other parts of the building connected with 

 them, which ought to have been supported by the 

 roof, and by this means not only destroying the inte- 

 rior ceilings, by producing large fissures in the plas- 

 ter of the partitions, particularly at their junctions 

 with the exterior walls, but also destroying the ap- 

 pearance of the exterior. Now it has been found, 

 that timber contracts very little in the length, even 

 less than many of the metals, and that the evil chief- 

 ly arises from the shrinking of king posts and queen 

 posts between the joggles. To remedy the defect, 

 it is here proposed to have neither king posts nor 

 queen posts, and, instead of them, to substitute long 

 rods of iron, which will perform the office of tie 

 braces, by suspending the tie beam, either in the 

 middle or in two equidistant places, by one or two 

 iron bars depending from the apex of the roof, and by 

 pitching the lower ends of the struts upon the one 

 or each of the places on the tie beam, supported by 

 the iron bar or bars; the upper ends of the oaid struts 

 supporting the principal rafters between their ex- 

 treme points at the required points where they are 

 loaded by the weight of the covering, and again 

 by suspending other rods of iron from these points 

 to the tie beams ; and thus a series of equidistant 

 fixed points of any required number, supporting 

 both rafters and tie beam, will be found, as may be 

 judged necessary, and without the smallest danger of 

 skrinking, and at less expence than truss posted or 

 joggle posted roofs, strapped or bolted to tie beams. 

 The iron of the straps and bolts in common truss 

 roofs, are of considerable expence ; the trouble of 

 boring, fitting in bolts, or wedging straps, is very 

 great ; and the making of king posts and queen 

 posts with joggles still greater, and the timber out 

 of which they are made increases the expences ; so 

 PLATE ^^ a ^ these sundries taken together, would be more 

 CXXIX. expensive than rods nutted and screwed. 

 Fig. 1. Fig. 1. Plate CXXIX. exhibits a design of a roof 



with struts and tie braces, calculated to span from 40 Construe- 

 to 50 feet, according to the strength of the timbers tive 

 and iron braces. ^ 



Fig. 2. represents the design of a roof constructed p tATi r"" 

 with struts and tie braces, calculated to span from 60 CXXIX. 

 to 80 feet, according to the strength of the timbers Fig. 2. 

 and iron work. The tie braces are here, and in the 

 last roof, supposed to be screwed and nutted above 

 the rafter, and below the tie beams. 



Fig. 3. shews a truss posted roof, with a king post Fl S- '* 

 and a pair of side posts on each side of the king post, 

 calculated to the same extent as the last roof; but, 

 from the number of joggle pieces between the struts, a 

 very small degree of shrinking in each will loosen the 

 struts, and consequently deprive them of their office 

 of supporting the rafters and tie beam. This cir- 

 cumstance cannot take place in any of the former fi- 

 gures ; and it may be farther observed, that the straps 

 and keys which are used in this design, will go a great 

 way towards the expence of the long iron screw bolts ; 

 and it may here be again repeated, that the trouble 

 of forming the truss posts with square abutments at 

 the joggles, the fitting of the iron straps, and the 

 cutting of the mortices for the wedges, is much more 

 trouble than the boring and screwing of the bolts. 

 The expence of the materials of the straps and keys, 

 and of the timber of the truss posts in this roof, 

 would exceed that of the bolts and nuts in the last 

 roof. 



Fig. 4. exhibits a design for a roof, which may ad- pig. 4.. 

 mit of an arched ceiling. The peculiarity of this roof 

 is, that the ties extend to the lower extremities of the 

 principals, and rise in the middle, so as to give great- 

 er elevation to the vaulted ceiling. This roof was 

 designed and executed by Mr Revely in the church 

 at Southampton, about the year 1797* and perhaps 

 was the first construction of the kind in this country. 

 The two ties are halved together at A ; but the parts 

 AB, AC perform only the office of ties, or are in a 

 state of tension ; while the parts AE and AD per- 

 form the office of struts, or are in a state of com- 

 pression. The king post AF, or an iron bolt, is a 

 necessary part of this- construction, and cannot by 

 any means be dispensed with. 



ON DOMES. 



Having now given some of the best forms of com- Domes, 

 mon roofs, we shall next proceed to domes, and show 

 how they may be constructed under various circum- 

 stances. 



If the dome be spherical, and have no lantern to 

 support the ribs, it may be constructed of boards in 

 two or three thicknesses, with the longitudinal joints 

 of the boards tending to the axis of the dome, and 

 intersecting the spherical edges, and the abutting 

 joints intersecting the sides of the ribs which tend to 

 the said axis. Let us now suppose the thickness of 

 a rib to consist of three boards, and suppose the cir- 

 cular pieces, which are to compose the ribs, to be all 

 prepared of equal lengths and breadths ; take one of 

 the lengths, suppose for the left hand piece at the 

 bottom, and lap the next higher length, which is the 

 middle piece, two thirds upon the lower piece ; take 

 another length for the right hand piece next higher, 



