GD & T Characteristics - A-4 Cylindricity

 

A-4: Cylindricity : 

This geometric feature combines the deviations at straightness and circularity at different locations for a tong cylindrical component. This characteristic is important for those cylindrical components to be fitted in their inverse cylindrical profiles and assure maximum surface to surface contact over the entire contacting cylindrical surface. Piston-cylinder assemblies at automobile engines, reciprocating compressors, reciprocating pumps; assembly of a cone pulley (stepped pulley) over the spindle of a lathe, etc. can be some illustrations. 

Fig.1. Cylindricity

The cylindricity symbol Shall consists of a circle of diameter equal to the height of any alphabet or numerical figure at the feature control frame; with to 600 slanting tangential lines on either side of height equal to I .5 times the height of any alphabet. Such a symbol, as usual, shall be placed in the I s! chamber and the second chamber shall indicate the permissible deviation at the cylindricity. 

The symbol shown shall mean that the entire cylindrical surface must be contained within two theoretical cylinders having a radial difference of the amount shown; i.e., 0.05 mm. However, both theoretical cylinders must be within the specified size limit at the same time.

Fig.1. Cylindricity

The best way of judging the cylindricity of any O.D. or bore; shall be to fit the component in an expanding sleeve or expanding mandrel of appropriate size. The expanding facility allows the mandrel or sleeve to get set to the appropriate size depending upon the actual size of the component. The actual contact between the pair can be seen with the help of some Prussian blue applied on the component to be tested and impression to be seen after the contact established. However, no measurement regarding the deviation of cylindricity can be done here.

For finding out the actual deviation at some component. the "V" block method shall be best suitable. However, various sets of readings are to be taken at different locations along the length of an object without disturbing the dial setting done initially. The difference between the extreme readings is expected not to be more than the stipulated amount. 

For finding out the actual deviation at a hollow cylindrical component, an appropriate measuring machine shall be most suitable where the component shall be static and a revolving dial around the theoretical axis of the component shall be expected to indicate the deviations. 

Adherence to the cylindricity to the maximum possible extent, assures uniformity at the surface stresses (bearing stresses), evens out frictional forces. prevents local wear of surfaces, reduces vibrations, and excessive heating of the assemblies in dynamic conditions. 

The geometric characteristics discussed till now, e.g., straightness, flatness, circularity, and cylindricity, do not require any datum at their specification. Further. they are rarely concerned regarding any maximum material condition or least material condition from the functional viewpoint. Hence, we rarely see the symbols like M or L at the concerned feature control frames. However, both of these specifications are necessary for the next characteristics under discussion.

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