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Fundamental limitation of traditional CNC control systems

Historically, waterjet and abrasivejet cutting tables have used traditional CNC control systems employing the familiar machine tool "G-code." However, there is a rapid movement away from this technology for abrasivejet systems. G-code controllers were developed to move a rigid cutting tool, such as an end mill or mechanical cutter. The feed rate for these tools is generally held constant or varied only in discrete increments for corners and curves. Each time a change in the feed rate is desired programming entry must be made.

A waterjet or abrasivejet definitely is not a rigid cutting tool; using a constant feed rate will result in severe undercutting or taper on corners and around curves. Moreover, making discrete step changes in feed rate will also result in an uneven cut where the transition occurs. Changes in the feed rate for corners and curves must be made smoothly and gradually, with the rate of change determined by the type of material being cut, the thickness, the part geometry and a host of nozzle parameters.



Make, the OMAX control software


The heart of the OMAX control system is the control algorithm that computes exactly how the feed rate should vary for a given geometry in a given material to make a precise part. The algorithm actually determines desired variations in the feed rate every 0.0005" (0.012 mm) along the tool path to provide an extremely smooth feed rate profile and a very accurate part. Using G-Code to convert this desired feed rate profile into actual control instructions for the servo motors would require a tremendous amount of programming and controller memory. Instead, OMAX uses the power and memory of the modern PC to compute and store the entire tool path and feed rate profile and then directly drive the servo motors that control the X-Y motion. This results in a more precise part that is considerably easier to create than if G-code programming were used.