M41-M42 Force Gear speed

             These M-codes are used rarely in NC programming for Milling and Used more in turning, any ways it’s good to know about the functions.

While working in CNC Machines We may have to select the Speed 100 to 1000rpms, whenever we work on the bigger diameters we may have to decrease the Speed and When We Work on the smaller diameters we may have to increase the speed, Increasing and Decreasing the speed can be done by changing the Gears on CNC machine.  Miscellaneous code called M-code control the machine controls.

M code 41, i.e., 

M41 is activated to select the Low gear to Decrease the speed.

M42 is activated to select the high gear to increase the speed;

These M-codes also used in Milling machines like Mandeli 5- axis machines.

Vericut Simulation takes more time while simulating M42???

In Vericut Simulation software When M42 code runs, the simulation take long time to finish the cycle.

You can follow the below step to overcome this slow Simulation problem in Vericut.

M42: Force High Gear.

1) Click on Collision
2) Uncheck visible stock and active tools’ Holders.

This makes the simulation faster and you can check this after finishing M42 Operation.

Defining a point PT in an Apt programming

                        In NC Programming the APT programs plays a major role, the geometries are defined by APT programming and then converted into G-codes giving motions to the CNC machine.

  Defining a point in the APT programming, the statement used is GOTO/P1; the programmer must know where P1 is located before the statement can be effective. P1 therefore must be described in a geometry statement, prior to its use in the motion statement GOTO/P1.

The geometry statement for defining a point is P1 =POINT/X co-ordinate, Y co-ordinate and Z  co-ordinate where, P1 is known as a symbol Any combination of letters and numbers may be used as a symbol providing the total does not exceed six characters and at least one of them is a letter.If the Z co-ordinate is zero and the point lies on the XY plane, the Z location need not be noted.Here “PT’ is a POINT. This word is a vocabulary word. Throughout, the designers of APT have tried to use words that are as close to English as possible. A slashfollows the vocabulary word and is followed by a specific description of the particular geometry, such as the coordinates of the point P1. AnAPT programming statement for P1 might appear as P1 = POINT/1, 5, 4. The 1 would be the X ordinate; the 5, the Y ordinate; and the 4, the Z ordinate. Lines

Examples for the Point definition in APT programming:

There are other ways of defining the position of a point, such as at the intersection of two lines or where a line is tangent to a circular, intersection of two circles, single point in space etc. following pictures shows the different ways of defining the Point in an APT programming.

Point in Space: Any point in the space can be defined as shown below.

APTSource code:
P1=POINT/4,5,2
P2=POINT/2,2






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Intersection of two lines: Point can be created by intersection of two lines.

APTSource code:
P1=POINT/INTOF, L1,L2













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Intersection of two lines: Point can be created by intersection of line and circle. there are two possibilities, it can be written as below.

APTSource code:

P1=POINT/XLARGE,INTOF,L1,C1
                       OR
P1=POINT/YLARGE,INTOF,L1,C1
---------------------------------------
P2=POINT/XSMALL,INTOF,L1,C1
                       OR
P2=POINT/YSMALL,INTOF,L1,C1

Note: The X and Y co-ordinates of P1 is Larger than the X and Y co-ordinates of P2.


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Intersection of two Cirlces: Point can be created by intersection of circles. there are two possibilities, it can be written as below.

APTSource code:
P1=POINT/XSMALL,INTOF,C1,C2
                         OR
P1=POINT/YLARGE,INTOF,C1,C2
---------------------------------------
P2=POINT/XLARGE,INTOF,C1,C2
                         OR
P2=POINT/YSMALL,INTOF,C1,C2

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Intersection of a radial line and a circle: Point can be created by intersection of circle with a radial line can be written as follows.

APTSource code:
P1=POINT/C1,ATANGL,20

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Intersection of a radial line and a circle: Point can be created by intersection of circle with a radial line can be written as follows

APTSource code:
P1=POINT/CENTER,C1










This is how the APT codes can be written in APT programming. All software generates the APTSource fiiles using the PPtables used while generating. PPTables are the machine defined files where all the cycles and the movements are in machining standardized format

APT programming

                   In general APT means“Automatically Programmed Tool”. The APT programming is done using the Cutter location (CL) points. APT can also be called as Cutter location File. APT programming can be classified into following below groups:

1) APT Geometry statements,

1)      Defining a point

2)      Defining a Line

3)      Defining a Circle

4)      Defining a Plane

2) APT Motionstatements.

3) APTPostprocessor statements.

When all these groups perform in a set then we have a complete program, Apt Geometry statements tells where the tool has to move, APT motion statement tells When and how the tool has to move will, APT postprocessor statements tells What tool has to move.

·         APT is also one of the languages that are output by many computer programs that produce CNC part programs directly from designs and drawings produced with CAD/CAM systems.

·         APT language is one of the computer languages designed to use with many NC machine tools.

·         APT was originally designed and used on mainframe computers and now it is available on mini- and microcomputers.

·         APT has also been recognised by the International Organization for Standardization (ISO) as a standardized language for NC programming.

·         APT is a very dynamic program and is continually being updated to use in CNC programming.

·         APT has the capability of programming the machining of parts in up to five axes, and also allows computations and variables to be included in the programming statements so that a whole family of similar parts can be programmed easily.

·         APT programing can be done by giving guide to the basic geometry andusing motion statements which is then converted by postprocessor to the machine readable G-codes and M-codes language.

CNC Procedure Step by step procedure

In a CNC machine we can create a CNC Program in hundreds of ways to machine the same work piece and all the ways we can expect the same finished part.

                                When you receive a 3D model to do CNC program, check the 3D Model for the numbers of ways we can place fixtures and number of setups required to finish the part. But, in addition to creating the CNC program, there is many other factors need to Know to machine the work-piece. There are many questions on your mind about how to hold the work, which cutting tools to be selected and which machining conditions to be used to get a perfect part on CNC machine.

Step #1: Selecting a Machine.

-       As described above we can machine a part in hundreds ways, but it’s wise to select the machine if you have many options in your shop floor. 

-       If the machining part has a difficult angles and surface profile, an ideal 3-axis machine may take number of setups consuming time and may be difficult to achieve the tolerance.

-       A 5-Axis machine can reduce the setup and give the best tolerance for the complicated parts.

-       A simple part can’t be machine on a 5-axis machine due to the high cost. So we need to decide wisely keeping in mind of machining time and the labour.

Step #2: Work holding Selection for the Part.

-       There are number of ways to hold a part on the machine, it always depends on the billet you are using. Billet may be a rectangular block, forging stock, casting block.

-       If you are using a rectangular block, you can use a machine wise on the machine table. If the block is big for machine wise you can use the push clamps to hold the block on machine table.

-       If the stock is an forging or a casting then you need to design the special fixture which can hold the stock comfortable and rigid.

Step #3: Choose the cutting Tools.

-       Choosing the tools for cutting the part is an important factor for the finishing the part. We need to choose the cutting tools depending on the type of material we are cutting.

-       For aluminium stainless steel cutting tools can perform well, but for the hard material like titanium and steel better consideration are carbide tools.

-       Before generating the programs it’s better to check the tools available in the shop floor, instead of waiting for the tools to be ordered.

-       Always shorter tools give more accurate results than the longer tools, so wisely use the tools in your programs depending on the height and depth of the part.

Step #4: Gather all Cutting Condition Data.

-       After the tools have been decided, calculate your cutting data such as speed & feed which can suit easy removal of material.

-       Recommended to use the cutting data given by the tools catalog given from tool manufacturers.

-       You can experiment using the different feeds and speeds later while optimizing the programs.

Step #5: NC-Axis Selection on the Part.

-       Decide the NC axis Point on the part. Example: you can select a corner of the part where X, Y and Z meet.

-       Selection of NC axis must make the machine operator to probe the part X, Y and Z easily. There is only on machine Zero axis, But you can create a number of NC axis i.e., Work co-ordinate offset.

-       If you are using a rectangular block, you can select the corner of the block for your NC axis XYZ=0, operator can probe the three walls of the block to make XYZ=0 on the machine and store the value on the machine Work offset. Usually we can use G54 which is standard..

Step #6: Creating a CNC PROGRAM.

-       An NC Program can be created in many ways, now a day’s using software like UNIGRAPHS, Catia, Mastercam etc. is the common way to create a NC program.

-       If it’s a simple program it can be done manually, such as program involving only drilling, reaming and tapping cycles.

-       After creating the tool paths’ using the software’s you can generate a NC-program which as G-codes directly within built postprocessor.

-       If you have a customized postprocessor loaded with the control of your machine, then the results are accurate.

Step #7: Checking the CNC PROGRAM.

-       There are number of ways to check the programs, program can be simulated for errors in the software’s used for generating the tool path.

-       You can use simulator software like Vericut, where we can build our machine and load the controls and test our G-code. The simulation can be actual like it’s been milled on machine.

-       If you want to verify only the tool paths you can use software’s like cimco edit. You can find much software on internet to visualize the tool paths.

Step #8: Setting up the CNC Machine.

-       Setting up your machine for testing the program is very important. Load all the fixtures decided to hold the part and mount the part as you designed while generating tool path.

-       Load the NC-program on the CNC machine memory or you can use the DNC software’s.

-       Load the tools into the tool magazine on the machine as per the tool numbers described in the program.

-       Define the individual tool offsets and store on the machine.

-       Probe and define NC program Zero and store G54 on the machine.

Step #9: PROGRAM PROVE OUT.

-       After all the setup. Here we go we can test our programs.

-       There are number of ways to test the programs if you are not sure of your program go well..

-       Testing the programs can be done on the dry run option on the machine.

-       Testing the programs can be done by cutting the wood instead of metal.

Good luck, have fun learning CNC Programming... 

If you have any questions and comments please let me know