pool (the end of which is 7/8 or 1 in. in diameter) upon
the table, and lay the pasteboard upon this. Push a large round nail
through the pasteboard into the hole in the spool. The nail should be
nearly as large as the hole. Use the large nail as a handle, and with
the shears cut around the edge of the spool end. Cut the washer as round
as possible, and be careful not to cut into the spool.

The holes in the washers will be a little smaller than the 5/16 bolt.
This will make the washers hold tightly to the bolt when you force them
on. Fig. 64 shows the bolt-core, with the washers in place. If you
cannot get a large nail, a lead-pencil, or sharpened dowel, will do to
force through the pasteboard.

[Illustration: Fig. 63.]

120. Insulation of Cores. While the covering on the wire would probably
be all that is necessary to thoroughly insulate the coil from the core,
it is better to wind a layer or two of paraffine paper around the bolt
(Fig. 65) before winding.

[Illustration: Fig. 64.]

[Illustration: Fig. 65.]

[Illustration: Fig. 65-1/2.]

121. The Coils of wire to be used upon the bolt-cores should be put on
with the winder (App. 93). For all ordinary purposes No. 24 or 25 single
or double cotton covered copper wire will do. It is better to put on an
even number of layers. The winding (See Fig. 70) begins at the nut-end
of the bolt, and by using 6 or 8 layers of wire, instead of 5 or 7,
both coil ends will be at the same end of the bolt.

122. Method of Winding the Coils. The winders used for bolt magnets are
described in App. 91, etc. We shall suppose that the washer, W, Fig. 70,
and the insulation, I, are upon the bolt before screwing it into the
winder-nut, W N. Make a pinhole, P H, in the right-hand washer, as near
the bolt-nut, B N, as possible. Stick about 6 in. of the wire through P
H, and wind this end around W N, as shown, to hold the wire. The supply
of wire should be upon a spool slipped onto some stationary rod (App.
23), so that you can give your entire attention to winding. Begin to
turn the winder slowly at first. Turn the handle towards you when it is
at the bottom, as in Fig. 70; that is, if you look at it from the side,
turn the handle clockwise. Let the wire slip through your left hand as
the turns are made, and guide it so that the turns will be close
together. If they go on crooked, unwind at once, then rewind properly.
You can guide the wire best by holding your left hand about 8 or 10
i