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Lecture 7 Maximum Material Condition Simmons and Maguire: 4th Edition Chapter 24: Maximum Material and Least Material Principles (Note: We do not cover Least Material Principles.)  When a shaft or a pin is at maximum material condition...

Lecture 7 Maximum Material Condition Simmons and Maguire: 4th Edition Chapter 24: Maximum Material and Least Material Principles (Note: We do not cover Least Material Principles.)  When a shaft or a pin is at maximum material condition, it is on its upper limit, (its largest diameter).  When a hole is at maximum material condition, it is on its lower limit, (its smallest diameter).  Maximum material condition is known as a ‘modifier’, because it alters the meaning of the geometric tolerance.  The maximum material condition is indicated by means of the capital letter ‘M’ inside a circle, depicted inside the tolerance frame; it can sit next to the tolerance digit, or next to the datum letter or letters, or both.  It is only applicable on straightness, the three attitude tolerances, and the three location tolerances.  Its application is restricted to features whose size is specified by toleranced dimensions incorporating an axis or a median plane; it can never be applied to a plane, surface, or line on a surface.  Maximum material condition should also not be applied to moving mechanical linkages and precision components such as bearings and gears, features such as threaded holes, or holes intended for an interference fit.  Any dimensional deviation away from maximum material condition serves as additional clearance on the given geometric tolerance.  It is possible to find a maximum material tolerance of zero on a drawing; it simply means that the upper limit indicates the largest permissible effective assembly dimension. Lecture 8 Keys, Keyways and Circlips Notes: refer to SUNLearn Simmons and Maguire: 4th Edition Chapter 19: Keys and Keyways (Note: there is no information on circlips in Simmons and Maguire) Keys and Keyways Keys transfer the load from a shaft, to the hole in the hub or body of a component on the shaft, such as a pulley or a gear. The sunken key is the most common type used, where one half of the key fits in the shaft, while the other half fits in the hub or body of the component. Common sunken key profiles:  Square key.  Rectangular key.  Round key Square and rectangular keys are called parallel keys. Parallel keys with rounded ends are called feather keys. Even though we only do keyway calculations with parallel keys, you must know the various other types of keys listed in Chapter 19 of Simmons and Maguire (4th Edition). Keys are usually manufactured out of EN8 key steel. A keyway in the hole of the hub or body of a component, is manufactured by a process called broaching. Keyways on shafts are milled with end or face milling cutters. How is a keyway dimensioned on a drawing? A typical question reads: ‘determine the dimensions of the keyway cut into the 35 diameter shaft or hole; the keyway has a tolerance of H8/f7.’ The width of a keyway requires a certain fit from the Hole Basis Table. We use the keyway table to merely determine the depth of the keyway. Follow the steps below: 1. According to the diameter of the shaft or hole, identify which row of the table must be used. 2. Look at the ‘Depth of Keyway’ columns. 3. If the keyway is cut into a shaft, subtract the value of ‘t1’ from the shaft’s diameter; this gives the dimension from the opposite side of the shaft to the bottom of the  keyway groove; (it is not dimensioned from the centre line, or one of the edges of the groove.) 4. If the keyway is cut into a hole, add the value of ‘t2’ from the ‘Feather Key’ column to the hole’s diameter; this gives the dimension from the opposite side of the hole to the bottom of the keyway groove; do not use the ‘Taper Key’ column. 5. Both ‘t1’ and ‘t2’ give the required depth of the keyway, plus additional clearance above the key – in other words, neither of the two dimensions require additional tolerance. 6. Look at the width ‘b’ of the keyway; follow the Hole Basis Table to give it the right tolerance according to the fit that is asked for. 7. On a 35 diameter shaft or hole, the width of the keyway is 10mm. 8. Ignore the ‘f7’ (shaft) part of the fit: a fit of H8 on a 10mm wide groove has a tolerance 10,02 of +22 microns (10 H8( )). 10,00 Circlips (Retaining Rings) External circlips hold components such as pulleys, gears or bearings in place on the shaft. Internal circlips perform the same function, but inside a hole on a component. Circlips are made from carbon spring steel. Special circlip pliers are required to locate or remove them. How is a circlip groove dimensioned on a drawing? We use the circlip table to determine the width, depth and position of the groove. Circlips are made for specific nominal diameters (‘d1’). Sizes ‘t’ and ‘b’ refer to the circlips and may be ignored. Diameter ‘d2’, width ‘m’, and minimum distance ‘n’ from the edge of the component to the edge of the circlip groove, are the critical dimensions that must be applied.