Fig. 28. Layer Winding for Small Coils.
The secondaries of large coils are made up of "pies" or "pancakes" from one-eighth to three-eighths of an inch in thickness. The "pies" are separated from each other by a triple thickness of blotting paper which has been thoroughly dried and then soaked in melted paraffin. In cutting the blotting paper, much labor may be saved if a metal template of the required size is first cut from sheet brass and then laid on the blotting paper, which is cut by scoring around the edge of the template with a sharp knife.
Fig. 29. Section Winder.
The "pies" are wound in a bobbin or form such as is shown in Fig. 29.
The disks or flanges are made of sheet brass and mounted on an arbor so that the form may be placed in a lathe or some other contrivance for revolving it. The core is beveled in order to facilitate the removal of a completed "pie" from the winder. The flanges of the winder are clamped against the core by two nuts placed on either side. The "pie" is removed by unscrewing one of the nuts and removing one of the flanges.
In winding silk covered wire it is first passed through a mixture of beeswax and rosin or a bath of melted paraffin. The excess of wax is removed by passing the wire through a slit made in a pad of paper or by rubbing against a piece of felt. Fig. 30 shows such a contrivance.
Fig. 30. Impregnator for Silk Covered Wire.
The wire passes from the reel over an ordinary spool down into the pan of paraffin, out of the paraffin, over another spool, and rubs against a piece of felt to remove the surplus paraffin. The spools are mounted with a screw and a washer so that they will turn without friction.