There are several methods used in describing an ellipse which the student no doubt has used in studying geometry, but the practical stair builder uses a trammel and block. The block is grooved through its center as shown in [Fig. 131], and the trammel is a strip of wood; a pencil is fastened on one end and pins are fixed at points to be found by trial near the middle. [Fig. 132] shows how the trammel is made. The pins slide in the grooves of the block, and the pencil marks the curve required.
Fig. 131.
Fig. 132.
Fig. 133.
[Fig. 133] gives a very comprehensive idea of the pieces before they are worked down. The pieces at the right and at the top are the moulds, and the mould for the rail is on the top of the piece which is seen in the front of the figure.
After having laid out the lines as directed make the moulds or templets out of thin stuff; then mark the stock (out of which the pieces of the rail are to be made), by the templets, and saw them out, either with a compass saw, or with the band-saw where it is convenient to do so.
It will be noticed that the piece out of which the curved or twisted piece is made is thicker than the piece which is parallel with the landing.