Lecture 2 | Axis in CNC | Dimensioning System | Program Structure in CNC | CNC Machining Programming

Hi students, welcome back in lecture number two of our course of CNC machining programming and let me just recapitulate what we have covered in our previous lecture. So in our previous lecture we have covered the introduction about the CNC machines, its advantages and disadvantages and then we have covered the evolution of NC system since its beginning to till now along with the different types of NC system that is conventional NC system, CNC and DNC system and in the end of our lecture we had covered the control panel of MCU that is the CNC control panel which is called as our MCU that is the controller of a CNC system in detail. So now let us start our today's lecture that is lecture number two. In today's lecture we will cover axes in CNC machines, dimensioning system with reference to absolute and relative system and then fundamental to manual part programming. Now let us start with axes in a CNC machines. All computer controlled machines are able to accurately and repeatedly control motion in various directions and each of these directions of motion is called an axis. Now depending on the machine type there are commonly two to five axes but nowadays there are such machines which are available in the market which are having more than five axes also. Additionally a CNC axis may either a linear axis in which the movement is in a straight line or a rotary axis where the motion is in a circular path. So in our CNC system you will find the axis of motion either in a linear direction that is in a straight line or either you will find the direction of motion in a circular path. So this figure shows the typical axis in a CNC system that is x y z and then a b and c. So here three are the translational axis that is x y and z are the translational axis. So let me just write here so x y and z are the translational axis and three we have rotational axis that is a b and c. So you can see in the diagram that if we have a rotational motion about the x axis then that axis is termed as a axis. So we can say here a axis or how we can define a axis that is when we have a rotation about x axis that axis is called as a axis and also when we have a rotation about y axis then that axis is termed as b axis and similarly for c axis that we can define our c axis when we have a rotation about the z axis and that axis is termed as c axis. So rotation about z axis. So I hope all these axis will be clear to you now that in our CNC system we will have a three translational axis that is when we have a linear direction or when the axis of motion is in a straight line that axis are termed as x y and z and when we have a rotation about either of x y and z then at that particular condition the axis are termed as a b and c respectively. Now let us understand all these axis one by one we will start with the z axis first. So z axis of motion is always the axis of the main spindle of the machine it does not matter whether the spindle carries the workpiece or the cutting tool. So z axis we always take along the spindle kindly remember this. On vertical machining centers z axis is always vertical and on horizontal machining center z axis is always taken as horizontal in case of turning centers also. Now positive z movement is away from the spindle that we will learn with the help of a diagram. Let us say this is a workpiece that we have a cylindrical workpiece and this is the spindle. Now if we draw a line that is an axis which is we are taking along the spindle this axis is a longitudinal axis and as we know this is our spindle along the spindle we are taking a longitudinal axis this is the workpiece. Now let me just draw a cutting tool also let us say this is our cutting tool. Now there are two conditions that when the cutting tool is coming towards the spindle or when the cutting tool is moving away from the spindle just like this let us say this is the workpiece and the workpiece we have kept the workpiece or are holding the workpiece in a chuck or in a spindle. Now this is the cutting tool when the cutting tool is moving in this way it means it is coming towards the spindle and when the cutting tool is moving like this it means the cutting tool is going away from the spindle. So this movement is termed as positive movement of the z axis and this movement is termed as a negative movement of the z axis. So this is what it is written over here that positive z movement is always away from the spindle. So there are two conditions now here one movement is this that is away from the spindle so this will be your positive movement of z axis and one moment is this it means now the cutting tool is approaching the workpiece or the spindle so it would be your negative z movement. So I'm just explaining you that in what conditions we will take positive z and negative z I hope it will be very clear to you. Now on vertical machining center as we know z axis is vertical let us say we are taking a spindle let us in case of a drilling machine and we have a cutting tool a drill bit so we know if we draw a line now a axis which is along the spindle this will be the axis if this is the spindle now and we draw a line or an axis along the spindle so along the spindle now this axis can be termed as z axis. So this is what it is written over here that on vertical machining center z axis vertical so this is a vertical machine and along the spindle we are taking a z axis which is vertical now and this is our turning center or horizontal machining center where the z axis is horizontal. So I hope now z axis will be very very clear to you now let us move ahead now let us understand what is x axis the x axis is always horizontal and is always parallel to the workording surface let me just highlight the key points that are written here so we will keep these key points in our mind when we are going to identify the x axis these key points are going to play a very important role when we will identify the x axis so first key point is that is the x axis is horizontal and is parallel to the workording surface and positive x axis moment is identified as being to the right when looking from the spindle towards its supporting column now let us understand this concept with the help of a figure let us say this is our workpiece a cylindrical workpiece and this is our spindle which is a workholding element here now as we know this is the spindle this is the workpiece and we are holding the workpiece in a spindle so now let us look into the surface of the spindle this will be the surface of the spindle and parallel to this surface is what which surface now this surface so parallel to workholding surface is this surface it means this axis is now termed as x axis so we can say here that this axis this axis is termed as x axis here and we know that if we take an axis along the spindle so that axis is called as z axis which we have just covered in the previous slide this is in case of a turning in case of turning but if we look at in milling machine then we have a workpiece just like this and workpiece is placed over a surface that is a workholding surface let us say this is the workholding surface so the workholding surface is this and parallel to this workholding surface which surface is parallel now we can easily identify that let us say this is the this is the surface where the workpiece is kept and it is holding just like this now this is the workpiece surface and parallel to workpiece surface is this surface this one so we can easily identify that this axis is termed as now x-axis and we know spindle will be here if this is the cutting tool so z-axis of motion is this this is the z-axis so it means this will be your z-axis and this will be your x-axis so I hope it will be clear to you now let us understand about y-axis y-axis is always at right angle to both x-axis and z-axis now as we know we know that where we will take x-axis and where we will take z-axis so at right angles to both the axis we will take y-axis so we will understand this with the help of a rectangular workpiece just like this this is the workpiece now we know in this rectangular workpiece this axis is termed as x-axis and this axis is termed as z-axis so I'm taking an axis over here if at this point I'm taking this axis as z-axis now this axis third axis is termed as our y-axis if you look into this workpiece we know this will be or this will be or x-axis this will be or y-axis and this will be or z-axis if this way this will be or x-axis this will be or z-axis and this axis will be or y-axis so all the axis are at right angles to each other so here we have finished with our axis that what is z-axis what is x-axis and what is y-axis now let us understand axis in a CNC lathe so this figure shows our lathe machine which we all have seen in workshops so this is a lathe machine which is having a flatbed now in this lathe machine these are the different components this is the headstock this is the tailstock and this is the workpiece that we have now if we take an axis which is along the spindle this is the axis so along the spindle is axis termed as z-axis or positive z-axis which is written over here and now this is the positive z now let me just explain you how we will take plus x this depends upon the type of the bed if we have a flatbed let us say this is the case of flatbed we all have seen a lathe machine conventional lathe machine in workshops and you saw there that the bed is a horizontal bed and there the cutting tool will approach the workpiece just like from here just like this so it is shown over here that this is the cutting tool this is the cutting tool so in a flatbed cutting tool will approach from here so this movement is taken as positive x movement this we know already that this is our positive z now in case of a slant bed or we can say in case of an inclined bed when the bed is inclined just like you will see in our CNC machines in our CNC lathe machines the bed is a slant bed and there the cutting tool will approach from the upside that is from this side like this so this is the cutting tool in case of a inclined bed so their tool move from the upper side so upper side means this movement is now termed as positive x so we can say this is your negative x this is a negative x here this is positive x so the positive movement of x-axis or negative moment of the x-axis it only depends upon the type of the bed kindly remember this thing now let me just explain you that it is written over here that maximum turning diameter is as x-axis and maximum turning length is z-axis now if you want to define the length of this workpiece how we will define we will say this is the length of the workpiece this is the length of the workpiece and we know also that this is the longitudinal axis and we define z-axis that are we always take z-axis along the spindle so this is z-axis that's why it is written over here that turning length maximum turning length is z-axis and if you want to define the diameter we know this is the workholding surface and parallel to workholding surface is this surface now and this axis is termed as our x-axis so if you want to define the diameter of this workpiece we will say this is our x-axis so maximum turning diameter will be your x-axis and turning length will be defined by z-axis I hope it will be clear to you now let us understand with the help of a 3d diagram that this is the workpiece we know the workpiece is rotating and this is the cutting tool and if we take an axis which is a longitudinal axis so if you want to define the length of the workpiece it means we can see from here to here this will be your length of the workpiece and if you want to define the diameter of the workpiece then we can say this will be your diameter this will be diameter of our workpiece so this axis we know this will be your x-axis because this is the surface which is parallel to the workholding surface and this is the surface this is the surface which is parallel to the workholding surface and this is the longitudinal axis or the axis along the spindle that we take z axis now I hope it will be very much clear to you now that axis in this machine how we will take positive x positive z negative x negative z how we will take now let us understand the axis in CNC milling machine so let us say this is our milling machine and this is the band where we will keep our workpiece so the axis are shown here as we know z axis we always know that it is along the main spindle so this is the spindle where the cutting tool is here we know this is the cutting tool which will be here and along the along the spindle we will take z axis so let me just explain this with the help of a figure so we know this is the x-axis so let us say let me draw a workpiece here this is the x-axis and this is the y-axis now this is the z-axis so let me just define the thickness we draw workpiece here it will be like this so we know this axis is your this is your bed or workholding surface we can say and parallel to workholding surface is which axis x-axis so that is why it is your x-axis so this will be your x-axis this will be our z-axis and the third axis which is perpendicular to both the x and z-axis is y-axis this is y-axis and this is your z-axis so which is written over here this is that now the cutting tool will approach the workpiece or it will move away from the workpiece so if the cutting tool will move away from the workpiece it means will be this way so it will be a positive moment if the cutting tool will approach the workpiece like this this will be a negative moment if the cutting tool is going away from the workpiece here in milling machine or in milling machine or drilling machine we will define the axis with respect to workpiece so here cutting tool is going away from the workpiece positive z moment and the cutting tool is coming towards the workpiece negative z moment okay so this will be your negative z so this is positive z this will be your negative z this will be your x x positive, y positive. So, in a typical simple Cartesian coordinate system we can say this at this particular point this will be your negative x and at this point this will be your negative y. So, now let us understand this with the help of one more figure let us say we have a table or a work holding surface just like this. Now, here z axis is same, but the x axis or y position is changed now. Now, here work piece if we draw a work piece it will be just like this here we know this is our x axis now this is your y axis and this will be your z axis. So, work piece will be like this now if you want to define the axis over here then we can say this is the work holding surface again this is the work holding surface and parallel to the work holding surface is your x axis. So, this will be your x axis and this will be your z axis and the third axis will be termed as your y axis. So, this is which is written over here this is your y axis this is your y axis this is your x axis x axis and this is your z axis I hope it will be very clear in both the figures are just same what we are doing that the position of the body is changed here. So, kindly do not confuse. So, in a summation we can say this is our three translation axis x y and z and if we have a rotation about the x that axis is termed as a if we have a rotation about y then that axis is called as b and if we have a rotation about z axis then that axis is termed as c axis. So, I hope now the axis in CNC machine in CNC lathe machine and CNC milling machine will be clear to you. Next we have dimensioning system. Dimensioning information in a workpiece drawing can be stated in two ways. The first is absolute dimensioning system and second is incremental dimensioning system. Now, let me just explain you this absolute and incremental dimensioning system. Absolute dimension system always refers to a fixed reference point. So, in absolute dimension system we have a fixed reference point and with reference to this fixed reference point we define the dimensions of the other points. This point has the function of a coordinate zero point. The dimension lines run parallel to the coordinate axis and always start at the reference point and absolute dimensions are also called as reference dimensioning system. Kindly remember this thing and in incremental dimension system every measurement refers to a previously dimensioned position. So, here the previous point will become the origin for the next point. Kindly note this. Incremental dimensions are distance between adjacent points or we can say in incremental dimensioning system we always take the distance between the two consecutive points. These distances are converted into incremental coordinates by accepting the last dimension point as the coordinate origin for the new point and incremental dimensions are also called as relative dimensioning system or chain dimensioning system. Now, let us try to understand the absolute dimensioning system and relative or incremental dimensioning system with the help of this figure. Now, this figure shows a step turning diagram. So, here we have six number of points that is P1, P2, P3 and so on up to P6. Now, what we are going to do? We are going to find out the coordinates of all these points P1 to P6 with the help of absolute and relative or incremental dimensioning system. So, diameters are shown over here. This is 10 and this is diameter 30, this is diameter 50. Respective lengths are also given 10, 20 and 30 and the fixed reference point which we are taking here is this point. This is the fixed reference point and we know at this particular point our X value and Z value will be 0. So, 0, 0 it is showing X0 or Z0. So, you can understand this with the help of this that this is the workpiece and suppose this workpiece is 60 mm or 6 cm and this is at center. We can say at center this center the diameter will be 0 or the length. It means the length is starting from here up to this it is 60. So, at this particular point your length is 0. Now, so 0, 0 that is X or Z will be 0. So, now let us try to find out the coordinates. Now, first with absolute dimension. So, we have written 6 number of points here then X and Z value. So, X is representing what? X is representing the diameter as we have discussed in previous slide and Z is representing length. So, always try to keep this in mind that X is representing the diameter and Z is representing the length. Now, at this point we have X and Z0. So, if we draw a axis this is we know plus moment and from this point if you go inside then it will be minus Z. It will be your X. This will be your X plus X let us say. So, now coordinates for point 1. At this particular point 1 we know diameter is how much? 10 mm. Length is 0 because length is starting from this point. So, 10, 0. At point number 2 the diameter is not changing but length is changing that we are coming towards the spindle. How much? 10 mm. Since we are coming towards the spindle so the moment will be taken here minus that is minus Z. So, X is remain same that is 10 and Z is changing now minus 10. So, 10, minus 10. So, for 3 we know now the diameter is changing. Diameter first it was 10 now it is 30 mm. So, for point 3 the diameter is coming 30 but length is not changing because length at this point P2 to P3 the length is not changing only diameter is changing. So, it will remain same that is minus 10 and for P4 now the diameter is same that is 30 but now the length is changing that is 20 but we are taking the dimensions with a fixed reference point. Reference point what is this? This is a reference point. So, from here to here now how much we have coming towards the spindle let us say 20 plus 10 that is 30. So, minus 30 mm we will take here minus 30 for point 4. Now coordinates for P5 it will be how much value of X is that is diameter 50 and there is no change in the length that is Z value it will be of minus 30 and lastly for P6 the diameter is not changing that is it will be 50 but now the length is 30 plus 30 now we will add this 30 more. So, 30 plus 30 will become 60 but with a reference to this particular point it will be your minus 60. So, I hope it will be clear to you that how we will take the dimensions or how we will find out the coordinates of the different points with respect to the absolute dimension system. Now let us try to find out the dimensions or the coordinates with reference to incremental or relative system for the same figure. So, for the P1 now in a relative system the diameter is how much 10 and the length is 0. The P1 remains same for both because it is the starting point. Now what is P2? For P2 now remember one thing this is a P1 and this is a P2. So, the previous point will become the origin now it means here it will showing your Z moment and upward it is showing your plus X moment. So, since we are moving in a straight line that is a horizontal we are moving in this way. So, we are going only in one direction. So, it will be your length wise that we are going in a length wise direction not diameter changing. So, it means always try to understand in our incremental or relative system one dimension will always be 0. So, now try to find out the coordinates now we know from P1 to P2 the length is how much 10. So, it will be your Z will be your minus 10, but X is 0 because this is the flat line X is not changing. So, X will be your 0 and Z will be your minus 10. Now let us try to find out the dimensions or coordinates for P3. So, now P2 to P3 how much the diameter is changing we know this diameter is how much this diameter is 10 mm if we draw a circle over here like this we know this is a diameter 10 and how much diameter is this is 30 mm. So, if this is 30. So, we know let us try to draw a line over here we know this diameter is how much if this is your 10 mm diameter and this is a 30 mm diameter 30 minus 10 is how much 20. So, this will be your 5 10 this will be your 5 10. So, it means now from P2 to P3 the diameter will be how much 10. So, for P3 diameter is how much X 10 and length. So, let me draw once again line that this is your P2 and this is your P3 and we are moving in one direction now only in X axis how much 10 this is your 10 mm diameter, but 0 in length because we are not moving in this direction we are moving only in the X direction. So, that is why it is written 0 and what is for P4 now if you understand this concept and for P4 you know we are moving in Z direction only how much 20 because the previous point will become the origin now this will become origin. So, it will be your plus Z it will be your minus Z it will be your X axis 0 for P4, but Z is how much we are moving from here to here how much 20 it will be minus 20 because we are moving for P3 to P4 we are moving in this way like this is P3 and this is P4 how much minus 20 and for P5 now we are once again you will apply the same relation over here the diameter is 50 total diameter up to here to here this is a 50 diameter. So, how much is this and we know this diameter is how much 30 diameter if this is your 30 diameter this is 50. So, 50 minus 30 will be 20 it means this will be your definitely because this is a symmetrical job this is 5 10 this is 5 10. So, in order to find out the coordinates for P5 like this is P4 and this is P5 we know this diameter is how much this diameter is 10. So, P5 X will be 10 Z is 0 10 and Z is 0 lastly for P6 we know this will be your previous point will become the origin this is a plus Z this is your X plus X this will be your minus Z. So, we are moving from here to here in this way how much 30. So, Z will be minus 30 and X will be 0 Z will be minus 30 and X will be 0. So, I hope now this will be very much clear to you because this is the basics of our CNC because we will always try to find out the coordinates for different points with the help of either absolute or incremental or relative system. So, if you find any difficulty in this then you can definitely comment in the comment box of this video. So, let us now move ahead now let us try to understand programming format. So, our CNC program consists of blocks we have different blocks in a CNC program and blocks consist of words and words consist of alphanumeric characters. So, let us understand this let us say this is a one complete block. So, one block is a complete NC instruction which consists of which consists of a words and words consist of alphanumeric characters. So, it will start with N, N stands for sequence number then we have G functions G codes which we will cover in our next lecture and we have X, X and Y are the dimensions as we know or the coordinates and M, M is the miscellaneous codes or the machining codes that we will learn also in our next lecture. So, this is a complete block and in this complete box it consists of words, words how because word consists of alphanumeric characters. So, if we take this N001. So, N is a alphanumeric character and 001 they are numbers. So, the complete instruction that is N001 it will become a word. Next if we take next information that is G01. So, G is a alphanumeric character and 01 is a number. So, G01, G01 it will become a word similar for X, Y and M. It means in a block basically we can say we have words and words consist of alphanumeric characters. So, in a programs in some estimation we can say in a CNC program it consists of blocks and blocks consist of words and words consist of alphanumeric characters. For example, let us say this is our CNC program and let me just take one line over here. Let us just say we are taking this line. So, here as we know G73 let us say it is written over here. This is our alpha character and 73 is a number but this whole information is becoming what? It is a word. So, one word U0.75 is another word W0 another word R4 is another word. So, one block of information consists of 5 words or more than 5 words also. So, programming format in CNC is word address format is the most commonly programming format that is used in our CNC machines. So, NC word as we know NC word is a collection of characters that is alphanumeric characters which is used to form an instruction and collection of NC word is called as a block and block of words is a complete NC instruction. I hope it will be very much clear to you. Now, there are different terms that we will see in our CNC programming that N stands for sequence number always remember this G is for preparatory functions which are also called as G codes. There are different G codes which we will take in our next lecture. M stands for miscellaneous functions or machining code which in short we can say these are M codes. X Y Z A B C we know these are the axis or the coordinates for a particular point I J K also and F function is for feed function. If you see F in a CNC program it means it is a feed function and S is the spindle speed function and T is for tool change. So, this is all for today's lecture. I hope this lecture will be clear to you and if you find any difficulty then kindly do not hesitate to comment or to email me on my email id which is shown here on my email id. I will try to answer your queries as soon as possible. So, thank you so much for joining me in this video lecture. Now, let us meet in our lecture number 3. Thank you so much.