Part head
A dividing head is required in practice to embody the even division of a circumference.
Mechanical dividing head
With the mechanical dividing head, an axis can be rotated by any desired angle with a worm gear. A perforated disc is located on the housing centered to the worm axis.
If one assumes, for example, that the worm gear has a 40-fold ratio, a full turn of the crank causes the spindle to turn 1/40 of the circumference. By setting the different hole spacings, even finer rotations of the spindle can be achieved.
Errors arise from the screw, which is used both as a measuring element and as a transport element, and they have an effect with the corresponding gear ratio. These errors increase due to the inevitable wear and tear during operation. The achievable accuracy of the mechanical dividing heads is therefore limited. It is also a prerequisite here that runout and wobble errors of the spindle are largely avoided by appropriate design of the spindle bearings.
Optical dividing head
In the case of the optical dividing head, the errors resulting from the screw transmission used for measurement are avoided. With him, the screw only serves as a transport element, while the spindle rotation is read off from a glass segment that does not wear out and sits on the spindle axis itself. After the setting to the desired angle value, the screw conveyor is swiveled out and the spindle is held in place by a brake. This must be such that tightening it does not change the desired setting. The first device of this type was brought out by Carl Zeiss, Jena, around 1920. Various other designs followed, all of which sought to achieve the highest possible indexing accuracy.
literature
- Heinz Zill: Measuring and teaching in mechanical engineering and precision device technology. 3rd, revised edition, VEB Verlag Technik, Berlin, 1974
