A serviceable pair of trammel heads for drawing-office work may be made from old or disused Dunlop valves. Remove the cap and nnts, cut off the flange shown at A (Fig. 2) with a file or a hack saw, and file the end to the shape shown at B (Fig. 3). Drill a |-in. hole at C (Fig. 3) right through each valve, and with a hack saw carefully cut out the slot (Fig. 3) 3/4 in. long by a full 1/8in. wide; file up smooth with a ward file. A piece of brass is fitted tightly in the hole in one of the valves,as shown by dotted lines D (Fig. 1), and soldered in place: the shank of an ordinary brass screw suits admirably. It is then drilled with a 1/16-in. hole, as at E (Fig. 1), to take the needle point, for which a piece of an upholstering needle, or the shank portion of a very fine drill ground to a point, can be used. Now get two small milled-head screws F (Figs, land 3), such as are used on gas brackets to keep the globe in place, and drill and tap a hole in each head to receive them. Take four pieces of watch spring G about 1 1/2in. long, and bend them to the shape shown at Fig. 4; these preveut the heads cutting the beam, and at the same time hold them in position when they are being moved along the latter. The pencils supplied with most diaries and pocket-books fit the heads nicely. For the beam, a piece of black walnut of any suitable length, accurately planed to 7/16in. wide by 1/8 in. thick and polished, is best. An ordinary compass pen may be made to fit into the end of the head by unscrewing it from the handle and filing it a little. Slide the heads on the beam, first placing the pieces of watch spring in the slots, the lower ones with the bend downwards and the upper ones with the bend upwards (see Fig. 1), and screw on the caps. Instead of cutting slots in the heads, holes may be drilled and a piece of steel wire used for the beam; but this does not answer so well as a flat piece of wood.

Trammel Heads made from Dunlop Tyre Valves.