In addition to the distinctive tubular base and distinctive lift off design, a twin spindle twin turret turning center is distinguished by the lopsided, triangular shape of the spindle. The lopsided triangular shape is a clear indication that the spindle is cast from a single piece of high-carbon steel. This type of casting is also noted for its smooth side walls.
It is the squareness of the top of the spindle that makes it distinguishable from a two-piece, casting in which the spindle and the top of the spindle are cast together. A turner can see the sides of the spindle but cannot easily view the top of the spindle unless they tilt the spindle backwards. The top of the spindle is made of a round, high-carbon steel, which is forged or welded to form a flat surface. A flat bottom on the spindle is another hallmark of this type of casting. With the exception of the flat bottom, all the other features of the cast spindle are the same as those of a cast cylinder.
When the spindle is lifted, it is pulled into the gap between the two halves of the twin turret spindle turret. At the top of the spindle, there is a flat surface for the support of the piston in the main bar. This surface also serves as the rim, to hold the crank handle in place.
The two halves of the twin turret spindle are screwed together to form a frame, and then the outer surfaces are filed down to fit snugly against each other. The top and bottom surface of the spindle are then joined together to form a more permanent portion.
Tightness and flow are determined by the flow being constrained through the frame. When the spindle is a true one-piece casting, the spindle can be positioned so that the two top and bottom surfaces are parallel to each other and the belt portion is resting on the smooth side of the top surface, while the crank handle rests on the sharp side of the top surface.
Rollers are manufactured by several methods. Sliding rollers are inserted between two blocks of wood, and the wood is held in place with wooden blocks.
A solid wooden block is pushed into the center of the spindle with a nail, and the block is then bonded to the top of the spindle. Where the spindle is hollow, a pair of rollers is inserted between two thin sections of hardboard, and the top of the spindle is then secured to these two sections.
For complex projects involving a full range of parts, a long handle (or combination of long and short handles) is used to direct the tooling when the spindle is pulled, as opposed to a sliding roller. Multiple, distinct spindle parts are used, where the spindle itself is a complete part of the assembly. When the spindle is part of an armature, the spindle is always on the inside of the armature.