1034 



TUBES 



2053 



which is made to revolve by attachment to a hollow spindle ; the cylindrical tube is 

 firmly held by the artizan when passing through the tool, and the thread is impressed 

 into the tube, or rather is indented in its passage through the tool or die, the tube 

 being lubricated with oil or tallow to aid the indentation and prevent the projecting 

 thread in the die from cutting or tearing the metal of the tube subjected to its opera- 

 tion. These tools or dies are not made of steel, but of chilled cast iron, their produc- 

 tion by the process of casting being more easily effected than by their being cut in 

 cast steel ; the friction being reduced to a minimum by the hollow tube yielding 

 readily to the pressure of the convex threads of metal in the die : the characters of such 

 tubes are represented in fig. 2052. A and B are the result of once passing the tube 

 through the tool ; c showing a diamond raised in centre, is produced by first passing 

 the tube through a tool with the thread right-handed, and then through a tool in which 

 the thread is left-handed, or in the reverse direction or 

 inclination to that through which it was previously passed. 



The tubes, Jiff. 2053, are formed of three separate tiibes 

 united together, each component tube being first drawn as a 

 separate tube : A being composed of three six-fluted tubes, 

 produced by being drawn through a correspondingly shaped 

 die; B by ordinary separately drawn plain tubes : and in c 

 the three tubes, in addition to the ordinary process of 

 drawing, are subjected to the operation of twisting as 

 already described in the last paragraph (under the head of 

 twisted tubes) ; the three tubes, eventually forming one 

 united tube, are then arranged parallel to each other and 

 the rope-like appearance of the tube, when finished, is pro- 

 duced by uniting them together by twisting, as strands in an 

 ordinary rope, each tube being filled with pitch and resin to 

 preserve its primitive tube-like form, and prevent its col- 

 lapsing in the process of uniting the three tubes into the 

 rope-like appearance when finished. 

 The Manufacture of Mandril-drawn Tubes, or Tubes perfectly cylindrical in their 

 internal and external diameters.- This variety of tube, is chiefly made in brass or 

 copper : in the former material principally used in the manufacture of optical instru- 

 ments, more particularly telescopes, dependent for their perfection in working on 

 tubes of the utmost degree of accuracy and perfectly cylindrical form, to ensure 

 steadiness when in work ; large quantities of mandril-drawn tubes arc also used 

 for the barrels of garden and other sjTinges, telescopic hearth-brushes and toasting- 

 forks, &c. ; while ordinary soldered jointed brass tube could not be successfully used, 

 or if used, would require an amount of labour to fit it for the purpose, obviously out 

 of place with the expeditious modes of working now in existence. The elasticity 

 resulting from the process of mandril-drawing, is another advantage in connection 

 with this process, arising from the condensation of the particles of the brass of which 

 the tube is made, these being forced down or compressed by the action of the un- 

 yielding steel tool, and the equally unyielding mandril or spit, which internally 

 supports the ordinary brass tube subjected to the process. An ordinary brass tube 

 is unequal in thickness internally throughout its entire length ; the two edges of the 

 strip from which it is made and -where it is soldered, are clearly seen ; and it is 

 evident that anything working piston-like therein, would do so only imperfectly. The 

 manufacture of light brass mandril-drawn tube is practised as follows: A carefully 

 t-clocted and well-forged cylinder of steel is turned to a perfect cylinder by means of a 

 slide rest, and carefully polished ; the brass tube made in the way already described, 

 is slipped on the mandril : in this position the mandril and sheath of brass is pre- 

 sented to the die in the drawbench, and is drawn through the tool which forms the 

 outside surface of the tube, compressing the metal, reducing the thickness, and com- 

 pelling it to embrace the steel mandril or internal support. The result is an clastic 

 brass tube, suitable for the purposes already enumerated. The air being expelled 

 between the tube and the mandril, considerable difficulty arises in releasing the tube 

 from the mandril, and this is effected by means of a collet or collar a little larger 

 than the steel mandril, but loss in aperture than the tube : 1bo collet is placed in 

 position of the drawing tool, the reverse end of the mandril being operated upon, as 

 in drawing the tube, the result is that the tube is withdrawn from its internal support, 

 and if the mandril has been correctly turned, a perfectly cylindrical tube is the result 

 of the preceding operations. In fig. 2054 the arrangement of mandril and tube to bo 

 drawn, and tool, are shown : A A, represents the mandril ; KB, the brass to bo operate;! 

 upon ; c c, section of the tool ; the thickness of lino to the left of the tool c c indicates 

 that part of the brass which has not been subjected to the operation of the dr;r\vi;,;, 

 tool. The release of the drawn tube is shown in fig. 2055 ; the collar or collet u is 



