GD & T Characteristics - B-2 Perpendicularity/squareness

 

B-2: Perpendicularity/squareness :

Many times, components call for squareness or perpendicularity between two surfaces, one axis, and one surface or two axes; to be within some reasonable limit. and frontal surfaces of a cylinder block; cylinder bore axis with respect to the face of a cylinder block; the axis of the post locator with respect to its resting face; can be a few illustrations. The loss at the perpendicularity can lead to improper alignments, loss at the utility. poor location and resting of the components during the processing and use etc.

 At any of these cases, shall be indicated by a symbol to appear as "⊥". The height of the vertical line in the symbol shall be 1.5 times the height of any alphabet or numerical figure at the feature control frame, similarly, the length of the horizontal baseline shall be two times the height of the alphabet. For indicating the of any feature; a datum is very much essential. A functional surface as a datum is the most ideal. However, depending upon the requirements, sometimes some axis or some center planes also can be the datum. 

FIG.01

A typical drawing involving a feature control frame for perpendicularity is shown. Here, the surface is expected to be square to the datum surface P within 0.2 mm. It means that the actual possible orientation of the surface Q can appear at the most like AA (or BE) where the extreme points like 1 and 2 shall be contained within two imaginary planes, perpendicular to P, having a separation of 0.2 mm. 

The deviation at perpendicularity can be best judged by a ''Try-Square" of appropriate size. When a try-square is aligned with the surfaces; then the shorter teg of the try-square is aligned with the datum and the long stem of the square is aligned with the surface of the component under test. Any uniformly increasing or decreasing gap is seen against illumination gives a judgment regarding the deviation at squareness. Instead of try-square to be aligned with the component, the component under test (if small) can be transferred on a surface plate and aligned with an angle plate.

If the deviation is to be measured, then a "V" block carrying a dial indicator is required to be held manually on a master cylinder (whose bottom face and axis have a perfect 90° angle). The oscillating dial is to be moved along different locations like 1, 2, 3, of the surface under test and the deviations can be recorded. Refer to the figure on the next page. 

The deviation at perpendicularity of one surface with respect to the other carries only one possible direction which is normal to the surface itself. Hence. no zone descriptor is essential to be mentioned at the concerned feature control frame. However, if it is a case of one axis to be perpendicular to some surface, then the possible deviation is in any radial direction i.e., in a circular zone. Accordingly, a zone descriptor symbol "' can be seen at the feature control frame. Perpendicularity of the of a post locator to its resting face, or the perpendicularity Of the liner bore or tappet bore to the mounting face can be some illustrative examples.

FIG.02

Accordingly, a typical feature control frame specifying the permissible deviation at perpendicularity of the axis of 50f7, post locator with respect to the adjoining face can appear as shown. The symbol for zone descriptor "φ" indicates that the permissible deviation Can be in any radial direction. The feature control frame for the perpendicularity shall mean that the axis Of the diameters can have any orientation but to be contained Within an imaginary cylinder of 0.15 mm diameter and height 100 mm. 

FIG.03

For checking for the qualification of such component; first of all. the direction Of misorientation Of the axis (due to lack of is required to be found out by applying 

To read More...Parallelism