Spindle control: Page 2 of 2

SPINDLE STOP

Normally, most work requires a spindle that rotates at a certain speed. In some cases, a rotating spindle is not al-ways desirable. For example, before programming a tool change or reverse a part in the middle of a program, the spindle must be stopped first. The spindle must also be stopped during a tapping operation and at the end of pro-gram. Some miscellaneous functions will stop the spindle rotation automatically (for example, the functions MOO, MO1, MO2 and M30). Spindle rotation will also stop automatically during certain fixed cycles. For a total control of program, the spindle stop should always be specified in the program. Counting on other functions to stop the spindle is not a good programming practice. There is a special function available in programming, to stop the spindle. 

In order to stop the spindle rotation, use function M05. M05 will stop either the clockwise or the counterclockwise spindle rotation. Because M05 does not do anything else (unlike other functions that also stop the spindle, such as MOO, M01, MO2, M30 and others), it is used for situations, where the spindle must be stopped without affecting any other programmed activities. Some typical examples include reversal in tapping, tool motion to the indexing position, turret change position, or after machine zero return, depending on the application. Using one of the other miscellaneous functions that automatically stop the spindle, the M05 function is not required. On the other hand, it does no harm to program exactly what is required, in a particular order. This method may result in a slightly longer program, but it will be easier to read and maintain it, mainly by CNC operators with limited experience. 

Spindle stop function can be programmed as a separate block, for example: N120 M05 

SPINDLE ORIENTATION

The last M function that also relates to a spindle activity is M19. This function is most commonly used to set a ma-chine spindle into an oriented position. Other M codes may be valid, depending on the control system, for example M20 on some controls. The spindle orientation function is a very specialized function, seldom appearing in the pro-gram itself. When M19 function is used, it is mainly during setup, in the Manual Data Input mode (MDI). This function is exclusive to the milling systems, because only specially equipped CNC lathes may require it. The function can only be used when the spindle is stationary; usually after the spindle has stopped. When the control system executes the M19 function, the following action will result

The spindle will make a slight turn in both directions, clockwise and counterclockwise, and after a short period, the internal locking mechanism will be activated. In some cases, the locking that takes place is audible. The spindle will be locked in a precise position, and rotating it by hand, will not be successful. The exact locking position is deter-mined by the machine tool manufacturer, indicated by the setting angle

SPINDLE SPEED - SURFACE

Programmed spindle speed should be based on the machined material and the cutting tool diameter (machining centers), or the part diameter (lathes). The general rule isthat the larger the diameter, the slower the spindle r/min must be. Spindle speed should never be guessed - it should always be calculated. Such a calculation will guaranteethat the spindle speed is directly proportional to the pro-grammed diameter. An incorrect spindle speed will have a negative effect on both the tool and the part.

Material Machinability

To calculate spindle speed, each work material has a sug­gested machinability rating for a given tool material. This rating is either a percentage of some common material,such as mild steel, or a direct rating in terms of its peripheral speed or surface speed. Surface speed is specified in feet per minute (ft/min) in English units, and in meters per minute in the metric system. An older abbreviation used for ft/min is FPM, meaning Feet Per Minute. The amounts of surface speeds indicate the level of machining difficulty with a given tool material. The lower the surface speed, the more difficult it is to machine the work material