Learning Mechanical Forms
: HOW THE DIFFERENT STRUCTURAL PARTS ARE DESIGNATED
Suppose, for example, we take the words segment
. Without a thorough understanding in your own mind you are likely to confuse these terms by taking one for the other. But let us assume you are to be called upon to explain a sector to some one who has no idea of terms and their definitions. How would you describe it? While it is true it is wedge-shaped, you will see by examining the drawing that it is not like a wedge. The sector has two sides running from
point like a wedge, but the large end of the sector is curved.
If you were called upon to define a segment you might say it had one straight line and one curve, but this would not define it very lucidly. Therefore, in going over the designations given, not only fix in your mind the particular form, but try to remember some particular manner in which you can clearly express the form, the shape or the relation of the parts.
For your guidance, therefore, I have given, as far as possible, simple figures to aid you in becoming acquainted with structures and their designations, without repeating the more simple forms which I have used in the preceding chapters.
—A series of arches with the columns or piers which support them, the spandrels above, and other parts.
—A curved member made up, usually, of separate wedge-shaped solids, A. K, Keystone; S, Springers; C, Chord, or span.
—A projecting mass of masonry. A, used for resisting the thrust of an arch, or for ornamentation; B, a flying buttress.
—The surface A formed by cutting away the arris or angle formed by two faces, B, C, of material.
59. Cotter or Cotter Pin.
—A pin, A, either flat, square or round, driven through a projecting tongue to hold it in position.
—A form of molding indented or notched, either regularly or irregularly.
—1. Latin cross, in the Church of Rome carried before Bishops. 2. Double cross, carried before Cardinals and Bishops. 3. Triple or Papal cross. 4. St. Andrew's and St. Peter's cross. 5. Maltese cross. 6. St. Anthony or Egyptian cross. 7. Cross of Jerusalem. 8. A cross patté or fermé (head or first). 9. A cross patonce (that is, growing larger at the ends). 10. Greek cross.
62. Curb Roof.
—A roof having a double slope, or composed on each side of two parts which have unequal inclinations; a gambrel roof.
—So called on account of its resemblance to a cup. A roof having a rounded form. When on a large scale it is called a dome.
—See King Post.
—A bracket with a projection not more than half its height.
—A mass of brackets to support a shelf or structure. Largely employed in Gothic architecture.