The method of making doors open exactly, so as to cut away the least quantity of wood, or to keep the nar row planes of the edges as nearly perpendicular to the face of the work as possible, depends upon the following principle.
Supposing a correct section to be drawn ; then, if the aperture be shut with a door to open in one breadth, draw a straight line from the centre of the hinge to the opposite angle of the plane ; perpendicular to which, draw another straight line, and this perpendicular will give the splay of the jamb which comes in contact with the edge of the door which is to be fastened or locked therein. If the aperture is closed with two doors, the principle is still the same, as it is only necessary to consider one of them to open at a time, while the edge of the other, which is bolted to the floor and soffit, is considered as a jamb ; then proceeding with the other half, which is thus left to turn on its hinges, as if it where a whole, in the same manner that we have now described.
Fig. 16. Slims the section of a door for a straigle wall.
Fig. 17. Is the section of folding doors. Here it be necessary to attend to the principle.
Fig. 18. Is the section of a door in one breadth gl a ctr • cular wall. Here the joints should tend to the ax a r f toe cylinder.
Fig. 19. Is the section of a door in a cylindrical wall, in two parts. In this the above method should be attend ed to.
Fig. 20. Is the section of a double door, to open to the space on the concave side. Ilere, in particular, the above method of making the doors open to clear the jambs should be attended to.
Fig. 21. Is the section of a single door, to open to the con cave side. Here the principle of making it open must also be attended to.
Raking Mouldings.
Raking mouldings depend upon the principle of a solid angle consisting of three plane angles, or what may be called a trihedral ; and this may be considered either as a hollow or as a solid, according as it may be used externally or internally. The mouldings are supposed to be placed in two of the lines of concourse, and to meet each other in a plane passing through the other line of concourse.
The raking mouldings of a pediment are placed upon a solid trihedral, the horizontal moulding being disposed upon the obtuse angle, and the raking mouldings upon the top of the tympanum. In this case, the mitre of the mould
ings is in the same plane with the line of concourse of the to o sides of the building.
The three planes which terminate in a point in the in side of a rectangular room, may he considered as a hollow trihedral. Now, if these three planes which constitute the trihedral be at right-angles, no difficulty can occur in con structing the mouldings, as each cornice may have the same section, and as the direction of both cornices are Perpendicular to the line of concourse of the two vertical.
sides of the room ; but where the cornice is perpendicu lar, and the other oblique, the case becomes the same as the preceding.
The same principle is also applied to the bars of a bow window, of which the sides form a polygonal prism. In this, the trihedral is considered as formed by the face of one of the vertical planes ; a vertical plane bisecting the two adjoining faces and a horizontal plane.
Let us suppose the inclination of the two planes through which the plane of the mitre passes, and the other two angles of the trihedral to be given. The projection of each mitre, and the figure of the mitre, or the section of one of the mouldings and the mitre line, must also be given, and we shall have sufficient data in order to ascertain the sec tion of the other moulding.
This construction becomes very easy, where the inclina tion of the two planes is a right-angle, and when the angle contained by the edges of the one plane is a right-angle, and that contained by the edges of the other an obtuse angle, as is the case with a pediment. The plane of the two ad joining walls is generally a right-angle, and the angle con tained by two of the edges of one of the planes is an obtuse angle, and that contained by the two edges of the other a right-angle.
This case affords a very easy construction ; it being only necessary to lay down the side of the building on which the pediment or inclined cornice is to be made, with a pro jection of the mouldings at the lower end, without any plan whatever, provided that the mouldings have the same pro jecture on both sides.