It meant that instead of having to turn a part at a fixed speed and feed, the part could be programmed in G96 which was a constant surface speed. Where diameters changed, particularly when facing, it made a massive improvement to tool life and surface finish as well as speeding up the whole process. So if you program. G97 S M3 Your chuck will start revolving clockwise at rpm.
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It is handier than spindle rpm because it is independent of diameter. For a given rpm, surface speed changes at every distance from the center. Surface speed is traditionally expressed in either feet per minute or meters per minute, so we can divide by 12 inches to the foot and arrive at SFM.
However, when we get near the center, the surface speed falls off rapidly. Pretty neat, huh? Interestingly, you can even buy manual lathes with the CSS feature. Note: Imagine a really large and not altogether well balanced workpiece held in a chuck.
The workpiece spins faster and faster, vibrating more and more, the closer the tool gets to the center axis. This is probably a bad thing. You should consider always specifying a D-word rpm limit when running in CSS mode to keep the workpiece from spinning too fast! Programming is so much easier. Surface speed is easy to come by for any tool you may use on any material. Better surface finish and tool life. The tool was designed to work at a particular speed. Having the speed change based on the diameter during a single cut does not create consistent results.
Faster cycles and shorter machining time. More consistent surface finish, regardless of part diameter. This is especially true if you use Constant Surface Speed along with g99 feed-per-revolution feedrates.
CSS makes no sense for center cutting operations, where the tool is at 0 on the X axis and only moving in Z. This happens, for example, during drilling, tapping, or reaming. No matter what surface speed you specify, the spindle will take off to its highest allowed rpm. Many controls require rpm mode during threading. The important thing when threading is to synchronize the motion of the two axes, not necessarily to maintain an exact surface speed over what amounts to a pretty small change in diameter from tip to trough of a thread.
Workpieces may not be held well enough to spin at max rpm. This can lead to some very serious accidents or even injury. It can slow you down. When you retract to go to another operation that may not even use CSS, why deal with decelerating the spindle only to have to accelerate it again for the next operation?
Use regular rpm mode G97 until the tool is positioned to begin a path. Switch to G96 at that point. Make the pass. Switch back to G97 before repositioning for the next pass. Use it only when the beginning and end of a cut will differ significantly in diameter. Set a prudent rpm limit based on the specific case for every use of G Exercises 1. Try some CSS mode programming.
Compare surface finish on a facing operation with and without CSS. Experiment with setting an rpm limit using the D-word.
G96, G97 and How To Calculate Surface Speeds
Controlling the spindle speed with G96 and G97 G-Codes We have two different modes to choose from when controlling the rotational speed of our component, the G96 constant surface cutting speed and the G97 constant spindle speed. G96 constant surface cutting speed The G96 command is used when we require a constant surface speed or cutting speed. This speed indicates the distance that the tool moves along the components surface per minute. As the tool approaches the centerline of the part, the spindle speed will increase until it reaches the maximum spindle speed for the machine. This is generally a bad idea as at this speed the centrifugal force may course the chick to fail at securely holding the workpiece.
It is basically the quantity that is used for defining the speed at which the tip of the tool is able to move over the workpiece. It is more convenient compared to spindle RPM as it is not dependent on the diameter. The surface speed ends up changing at each distance from the central point, for any particular RPM. These are the two modes that you can select when you are trying to control the rotational speed of your component. The G96 is for constant cutting surface speed and the G97 is for constant spindle surface speed. What is the G97 Code? For most of the controls, you get to just enter the G96 code for telling the machine to go at a constant surface speed.
Instrucción G96 (Velocidad de corte constante)
G96 G-Code: Constant Surface Speed CNC Programming