Motion Statements Apt programming

                  

So we have learnt how to define the Geometries from previous learning’s, now we can discuss how we can do the APT programming using the different geometries connecting each other and to give a motion to the tool to move forward continuously. APT motion statements are based on the concept that a milling cutter is guided by two surfaces when in a contouring mode.These surfaces are called the “part” and the “drive” surfaces are shown in below figure. Usually, the part surface guides the bottom of the cutter and the drive surface guides the side of the cutter. 

These surfaces may or may not be actual surfaces on the part, and although they may be imaginary to the part programmer. The cutter is either stopped or redirected by a third surface called a check surface. If one were to look directly down on these surfaces, 

The cutter can be stopped by giving an end point or a check surface. When cutter is moving towards to an end point or the check surface or it may move TO it, ONTO it, or PAST it, as illustrated in below figures.

When defining a continuous tool path statement after the cutter meets the check surface, it may go right denoted by the APT command GORGT, or go left, denoted by the command GOLFT as shown in the below figure. So this combination of the moving to check surface and then continuing left or right of the check surface to the next drive surface creates the continues tool paths.

In some cases the cutter may go forward, instructed by the command GOFWD, The command GOFWD is used when the cutter is moving either onto or off a tangent circular arc. These code instructions are part of what are called motion commands

Below figure shows the definition of the continues tool path and explained as below:

The cutter is moving along a drive surface, L1, toward a check surface, and stops to the line L2.

The APT motion statement for this move is: GOTO/L2,

When it arrives at L2, the cutter will make a right turn and move along L2 and past the new check surface L3. Note that L2 changes from a check surface to a drive surface the moment the cutter begins to move along it. The APT motion statement for this move is: GORGT/L2, PAST, L3

Then the cutter moves along L3 until it comes to L4. L3 now becomes new the drive surface and L4 becomes the check surface. The APT statement is:

GORGT/L3, TO, L4,

The cutter is moving to the right, it makes a left turn if one is looking in the direction of travel of the cutter. In writing the motion statements, the part programmers must imagine they are steering the cutter. The drive surface now becomes L4 and the check surface, C1. The APT statement is: GOLFT/L4, TANTO, and C1

This movement could continue indefinitely, with the cutter being guided by the drive, part, and check surfaces. The APT statement is: GOFWD/C1, TANTO, and L5.

Start-Up Statements:For the cutter to move along them, it must first be brought into contact with the three guiding surfaces by means of a start-up statement. There are three different start-up statements, depending on how many surfaces are involved.A three-surface start-up statement is one in which the cutter is moved to the drive, part,and check surfaces, as seen in below figure, 

A one-surface start-up is one in which the cutter is moved to the drive surface and the X−Y plane, where Z = 0, as in below figure

With the two- and one-surface start-up statements, the cutter moves in the most direct path, or perpendicular to the surfaces. Referring to (three-surface start-up), the move is initiated from a point P1. The two statements that will move the cutter from P1 to the three surfaces are:

Apt sourcecode:
FROM/P1

GO/TO,DS,TO,PS,TO,CS

Five-Axis Machining: Machining on five axes is achieved by causing the APT program to generate automatically a unit vector that is normal to the surface being machined. The vector would be described by its X, Y, and Z components. These components,along with the X, Y, and Z coordinate positions of the tool tip, are fed into the postprocessor,which determines the locations and angles for the machine tool head and/or table.

Always the Apt programs may be different, but when the apt program is posted using postprocessor, the the standard Gcode will be generated, only the mcode will be machine dependent.

Enjoy learning Cnc programming and Apt programming.