A tube may be cold drawn over a mandrel, as previously described, until its wall is too thin to stand further pulling through the die. If the tube wall is to be made thinner, further drawing is done by placing the tube over a solid steel arbor and drawing it down as shown in Fig. 74. The tension of drawing is then taken by the arbor and the tube wall may be drawn very thin. Large rigid arbors are pushed through the die. When the drawing is done, the tube is removed from the arbor by hammering it gently with a wooden mallet or by passing it between rolls.

Very small tubes are made without a mandrel. They are first cold drawn over a mandrel to a diameter of 1/2 inch or less and are then "sunk" by drawing through the die without a mandrel.

Fig. 74. - Arbor for Drawing Thin Tubes.

This reduces inside and outside diameters, but increases the thickness of wall. If the wall is to be very thin, an arbor is placed in the tube after it has been sunk nearly to the required inside diameter and the wall may then be drawn down as thin as required.