Fig. 2288.
Put the eyes together with the pin in and let the two lowest places on the edges coincide. Then file a flat place clear across them, as shown in [Fig. 2288] at f, making it parallel to the pin, and, say, down to within 1⁄100 of the finished depth. To test the parallelism of the flat place, take out the pin and apply to the flat place a square, rested against the radial face of the double eye, or measure its distance from the hole of the eye on each side of the double eye, that is at each end of the hole.
Fig. 2289.
When it is true and down to the required size, put the eyes together and let their relative positions be such that the flat places do not coincide, and that on the double eye will serve as a guide to carry the filing around the single eye, while that on the single eye will serve as a guide to carry the filing around the double eye, as will be seen on reference to [Fig. 2289], in which the flat places a, b on the double eye serve as a guide to file c down to, while the flat place on the single eye at d is a guide to file the metal at e, f down to, and it is obvious that by moving the eyes to different positions the eye may on that side be filed true and to circle.
When the filing has thus been carried around as far as the movement of the eyes permits on that side, turn the single eye over in the double eye, and they will appear as shown in the end view, [Fig. 2290], a being the filed side of the single and e d that of the double eye; hence the metal at c, b must be filed down level with a, and that at f down level with e, d.
Fig. 2290.