After two or three of these had been made, Harry decided that they were too small to suit him, and a new design somewhat larger was worked out on paper. It was a little more difficult to follow, because the outline had two reversed curves, but the boys were too busy and interested to be daunted by a trifle like that. ([Fig. 12].)
Ralph suggested simple picture frames, and this brought the new problem of cutting out an opening for the picture.
Fig. 13. Picture frame with elliptical opening
The first design they tried is shown in [Fig. 13]. Ralph had to show Harry how to make the ellipse with compasses by first constructing two squares or rectangles touching, and with both diagonal lines in each square. By taking for a centre the point where the squares touch, as a and b, and using the length of a diagonal line as a radius, two arcs were drawn at x and y. The ellipse was finished by taking c as a centre, and the distance c d as a radius, to draw arc z, and the other end was finished in the same way.
Ralph explained that this was not a perfect ellipse, but would answer for a small picture frame. The drawing was easy compared to the question of how to cut out the wood to this curved line.
Fig. 14. Using the coping saw