cnc training in chennai
Some limitations of CNC controlled machines
Depending on their age and sophistication, CNC machines can be limited to the capabilities of their control and drive systems. Most CNC controllers only understand straight line movements and circular arcs. In many machines, the arcs are restricted to the principal XYZ planes as well. Rotary axis movements can be considered like linear movements, just degrees instead of distance. To create arc movements or linear movements that are at an angle to the principal axes, two or more axes must interpolate (move precisely in a synchronized manner) together. Linear and rotary axes can also interpolate simultaneously. In the case of five axis machines, all five must be perfectly synchronized – no easy task.
The speed at which the machine controller can receive and process the incoming data, transmit commands to the drive system, and monitor the machine’s speed and position is critical. Older and less expensive machines are obviously less capable in this, much in the same way that an older computer will work less well and more slowly (if at all) on demanding tasks than a newer one.
Interpret your 3D and spline data first
A typical problem is how to set up your files and do your CAM programming so that the machine executing your parts will work smoothly and efficiently with the data. Since most CNC controls only understand arcs and lines, any form that is not describable with these entities needs to be converted into something usable. Typical things that need converting are splines, i.e. general NURBS curves that are not arcs or lines, and 3D surfaces. Some desktop machine systems are not able to understand circular arcs either, so everything must be converted into polylines.
Splines can be broken up into a series of line segments, a series of tangent arcs, or a combination of both. You can imagine the first option as a series of chords on your spline, touching the spline on each end and having a certain deviation in the middle. Another way is to convert your spline into a polyline. The fewer segments you use, the coarser the approximation will be, and the more faceted the result. Going finer increases the smoothness of the approximation, but also dramatically increases the number of segments. You can imagine that a series of arcs might be able to approximate your spline within tolerance with fewer, longer pieces. This is the main reason for preferring arc conversion over simple polyline conversion, especially if you are working with older machines. With newer ones, there is less of a problem.
Imagine surfaces as the same kind of spline approximation, just multiplied many times in the across direction with a space between (usually called the stepover). In general, surfaces are done using all line segments, but there are situations where arcs or a combination of lines and arcs can also be used.
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