A dividing head is a device used to rotate the work piece around a third machine axis; the third axis is typically referred to as the C axis. The goal of the dividing head is to help create accurate multi axes machining operations on a work piece. Therefore, the dividing heads are the necessary component to a number of CNC milling machines. The dividing head may sometimes be incorporated with a rotary table in particular machining operations. The dividing head is also known as the spiral head or the indexing head.
In the modern CNC machining settings, the dividing heads are crucial since they allow the work pieces to easily and precisely rotate at preset angles. As a result, the dividing heads can be found on many multi axes CNC turning centers for operations such as milling, drilling, grinding, or boring, etc. To be exact, the dividing heads are used to divide circumference of a work piece into equally spaced divisions when milling gear teeth, squares, hexagons and octagons. The orientation of the dividing head can be either right handed or left handed on a turning center depending on which end the mechanists have it assembled. They are also used to rotate the work pieces at a predetermined ratio to table feed rate.
There are three major components to a set of dividing head. On a regular dividing head model, there are the footstock, the center rest, and the headstock. The headstock is the key component to the set and it is the part that is commonly referred to as the dividing head. Inside the headstock, the most fundamental parts are the swivel block, the spindle, the worm and the direct indexing plate. The swivel block is mounted at the center of a dividing head. It is used to enable the headstock to be tilted from five degrees below horizontal to ten degrees beyond vertical.
The swivel block looks like a gear and has teeth that contact the worm. The worm is mounted in swivel block with the 40-tooth worm wheel on a worm shaft. When the worm shaft rotates, the swivel block rotates accordingly. On the end of the worm shaft, there is the direct indexing plate. The direct indexing plate is engaged by the index pin and attached to the front of the spindle.
The indexing plate is also called a dividing plate. On all types of dividing heads, the worm is turned by means of a handle. The handle may contain a retractable pin or a pin that can be locked into a hole in an indexing plate. This design has to do with the indexing methods that the dividing head shall apply. The indexing plate has multiple holes that space equally around the plate. The index pin can be set to fit in any of the holes. By using the index pin, the movement of the spindle on the dividing head can be made by any number of spaces.
The indexing plate is the key to dividing the circle. Typically speaking, there are three indexing plates on a dividing head and each of the plates has a number of rings of holes. A turn of the handle can be divided into the number of holes in the particular ring. On some indexing plates, the holes are spread only to the halfway via the plate and there is another set of rings of holes on the other side of the plate. With such design, the plate can be fitted and used either way around.
There are four essential ways that the dividing heads apply for indexing: the direct indexing, the simple indexing, the angular indexing and the differential indexing. The direct indexing is the simplest form of indexing. The direct indexing is performed by disengaging the worm shaft from worm wheel by means of disengaging the drive gear. This form of indexing is used for the quick indexing of the work pieces when cutting flutes of a milling cutter, or when cutting hexagons.
The simple indexing accomplishes the work piece positioning with the crank, the index plate and the sector arms inside the headstock. In this form of indexing, the worm that attaches to the crank must be engaged with the worm wheel on the spindle of the dividing head. The 40 teeth on the worm wheel are needed to achieve the turns on the index crank. One complete turn on the index crank causes the spindle and work to rotate one fortieth of a turn.
One complete turn of the index crank causes the work to rotate one fortieth of a turn and the one fortieth portion of three hundred and sixty degrees equals nine degrees. The angular indexing is the method that applies the following formula: the turns of the index crank equals the angle required divided by nine. When the index plate does not have the combinations of particular angular spacing, the differential indexing is used.
The differential indexing refers to the indexing method that does not apply the one fortieth worm assembly. Instead, the indexing plate is driven through a bevel gear system. When the index plate is in an unlocked position, it moves as the index crank is turned. The plate is rotated by gearing from the spindle.
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