Method and apparatus for making step wall tubing

Apparatus for providing the wall of an elongated tube with a plurality of precisely located thick and thin wall portions lengthwise of the tube comprising:

• a drawing die having a relatively wide mouth for receiving an end of a tube,
• a drawing bulb for insertion into the tube, said bulb having a constant cross-section and a relatively square nose for entering into the die mouth while being located within the tube,
• means for inserting the nose of the bulb with required precision and quickness into the mouth of the die to provide each thin wall portion and for withdrawing the nose from the die mouth to provide each thick wall portion while drawing the tube,
• a controller for controlling the means for inserting and withdrawing the bulb,
• means for pulling the tube through the die, and
• a rotary encoder for measuring distance increments of tube travel as the tube is pulled through the die, and for outputting signals that are representative of such increments
• said rotary encoder being connected to the controller such that the signals are directed to the controller, the controller, in response to the signals, being effective to precisely control the occurrence of bulb insertion and withdrawal.