CNC notes

Lately I have been reading up on Cnc, G codes and the like, here are some notes I made while studying the subject from Virtual Machine shop.

CAD/CAM, computer aided design and computer aid manufacturing, along with CNC, computer numerically control, is the basis of how parts are machined in a modern machine shop. CAD is essentially an engineering drawing on a computer, changes can be made immediately if needed also, with modern software, and the part can be tested, and analyzed before manufacturing. Now that the part is drafted and is in a computer file CAM comes into play, this aids in the actual manufacturing process. In this case a CNC part program can now be generated which includes a tool path, tools to be used, feed rates, work holding and coolant. In using a CAD/CAM system the steps are

1. CAD, computer assisted drafting
2. CAM, computer assisted manufacturing
3. NC, G & M CODE generation
4. Shop Floor, CNC machine controller

CNC Control- Point to Point

A CNC controller is made up of two systems, mode of the control, and the type of control loop. The mode of control can be either point-to-point or continues path, and the type of control loop can be closed-loop or open-loop. The mode of control controls the tool as it moved to position or along the cutting path. The point-to-point system can also be referred to as the positioning system; its function is to move a tool from one point to another specified point. This is to perform such operations as drilling, punching, boring, reaming and tapping. There are three paths that the tool can follow to move from point to point; the Axial Path, the 45 degree path, and the linear path. With the axial path the tool moves in a right-angle path parallel to the two positioning axes, X and Y. The tool moves first moves along the X axis till it reaches a specified point, then along the Y axis till it reaches a specified point. Because one axis is moved at a time this is the slowest method.

The 45 degree path moves the tool at a 45 degree angle until x one of the axes is lined up with its new position. Then the tool moves along the axes to the specified coordinate position. At first both X and Y move at once till one of the specified coordinates is reached then the tool moves in an axial path mode to the specified coordinate position.

In the Linear Path mode the controller can synchronize the motion in both axes thus generating a linear path. This is the quickest method for moving point to point; however, more sophisticated equipment is needed to coordinate the speed of each axis so a straight line can be maintained.