 This is Shila Ratna Banshwade from Walton Institute of Technology, Singapore. As a part of machine drawing curriculum, we are going to see the topic BIS Conventions, BIS Conventions that is Bureau of Indian Standards and its conventions and specifically we will be dealing with Geometrical Tolerances and Surface Roughness. Now, I suggest you to pause the video at this moment and recall the BIS Conventions that we used or the Tolerances, Dimensional Tolerances that we have studied in the previous videos. Moving further, students will be able to use Geometrical Tolerances and Roughness Symbols. So, at the end of this sessions or at the end of this video, you will get acquainted with the Geometrical Tolerances and what are the Roughness Symbols. Moving further, we have seen Dimensional Tolerances. Dimensional Tolerances deals only with the dimensions. What kind of value is required or what kind of value can be achieved to Tolerances? Now, what is Tolerances? Tolerances is an allowable limit. It is an allowable value that is given to a manufacturer unit so that that particular component can be manufactured with that particular tolerance. For example, if you want to manufacture a shaft of 50 mm diameter, allowance is provided to the manufacturer that for 50 mm diameter, he can manufacture or a shaft of 49.5 mm is also allowed or a shaft of 50.5 is also allowed. So, a range of 49.5 to 50.5 is allowed for a shaft of 50 mm diameter. So, this tolerance or this allowance, these limits is called as Tolerance. And what example that I have discussed with you is an example of dimensional tolerance where only the size is suggested or the size has a tolerance. But as far as components are required, merely dimensional tolerance does not satisfy everything. Does not satisfy everything. Like for example, a shaft may have uniform diameter throughout. Uniform diameter throughout but it might not be circular. Dimensional tolerance says that it has uniform diameter with the allowance but it is not circular or a component is circular in all cross sections. But it is not straight. Here you can see some deformations in the shape, some deformations in the shapes. See this is circular throughout but it is not straight. Here the cross section or the shape here is up and down. Here it is straight but it is not exactly circular. So, even though if you have dimensional tolerance is such kind of draws, drawbacks can be seen in the components. And to control this that are related to the form rather we need to go for geometrical tolerances. So, to have an addition to dimensional tolerances we go for geometrical tolerances that deals with the forms of the components, shapes of the components. Dimensional tolerances goes for the size of the component whereas geometrical tolerances goes for the form or shape of the component. We will move further. In geometrical tolerances are defined as these are the maximum permissible overall variations of a form. It is maximum possible and overall permissible variation of a form or position of a feature. Position of a feature is if you have two concentric circles to what extent the concentricity might be deferred. So, possible position of feature. Geometrical tolerances are used to specify the required accuracy in controlling form of a feature. They are used to control the shape of a feature. Shape or form of a feature. Feature a component. They also ensure correct functional positioning of the feature. Correct functional positioning is two concentric circles should be positioned at the same center point. Then interchangeability of components. If you manufacture two components with dimensional as well as geometrical tolerances for one specific application and if you want to use same component in some different application you need not to manufacture the component separately. From one system to another you can interchange that particular component. So, interchangeability of the component that is one hexagonal note that from one application can also fit similar unit without any modifications. So, interchangeability. Then we have facility to assemble of mating components. Easy assembly and disassembly can be obtained. With geometrical tolerances. This is how geometrical tolerance is represented. This is how geometrical tolerance is represented. Here this is the surface on which you want to show the geometrical tolerance so called as datum feature or reference feature. This is the component. Then you have a datum triangle which rests on the datum surface that is reference triangle or reference feature. Then you have a straight line with a box and you name it as with certain capital letter called as datum letter or reference letter. So, this is the reference surface. This is the reference triangle. Then a straight line and then a reference letter included in a square box. Now how exactly it is written? You can see over here. This is the datum surface or surface to be tolerated. I have a tolerance or reference surface. This is the arrow. You can use arrow or this reference datum triangle. Then a straight line and then a horizontal line as called as leader line. Straight and horizontal line called as leader line. Then we have a rectangular box and in that we have three square boxes or three different boxes. The very first box represents the tolerance symbol. What kind of tolerance do you want to have with that particular symbol? This symbol represents parallel. When you want to show parallelism between two surfaces, two parallel surfaces, you go for this symbol. With the tolerance of, this is the tolerance. What extent the parallelism between two components can be varied? 0.02 microns, the parallelism between two components can be varied or two surfaces can be varied. With which surface? You name the two surfaces A and B and you represent this on surface B. This is parallelism to a variation of 0.02 with surface A. This is how geometrical tolerance is being represented. Moving further, these are certain indication of feature controlled systems as you can see on screen. The first one is form of single feature. Form of single feature, you have cylindricity, flatness, straightness and so on. So these are the conventions or these are the symbols. Then you have orientation of related feature. How the feature is oriented? That is parallel, perpendicular, angular and so on. And this is positioning. Then you have position of related feature. Position of related feature. That is concentricity, symmetry or there is certain run out. So these are some of the symbols that we use for geometrical tolerances. Moving further for some examples. See what is correct and what is incorrect. You can see how to dimension the component using geometrical tolerances. Then we have certain examples. So how straightness is being mentioned. So this is how straightness is shown. Straightness of these two lines. Then flatness of this surface. Flatness is these are the symbols that we have seen with the variation of with the tolerance of this. Then circularity tolerance. Cilendricity tolerance. Then parallelism tolerance. These two surfaces are parallel with this value. Perpendicular. These two surfaces are perpendicular with the variation of this. See this is perpendicular to surface A with the variation of this. Here you have name D. This is parallel to D with the variation of this. 0.01. Concentricity tolerance. Symmetric tolerance. Then coming to roughness grids. These are certain roughness grids. Roughness is the texture that you have on any object. And these triangles show to what extent the surface is smooth. This represents a hard bit rough surface and as the triangle goes on increasing the smoothness of the surface increases. And these are the roughness grids that are used to represent either you can use this triangle or these values. N1 to N12. And these are the values for each zone in micrometers. These are the references. Thank you.