Approximate construction for nuts and bolts Figs and

Stage 1

1 Draw a circle in the plan position, 2D in diameter, where D is equal to the thread size. In this example let us assume that the thread size is M20.

2 Draw a hexagon inside the 40 mm diameter circle and inside the hexagon draw another circle tangential to the hexagon on the six sides. This circle is the projection of the chamfer which can be seen on the front elevation.

Fig. 16.2 Stage 1

the nut thickness is 0.8D. Project the four corners of the hexagon to the front elevation. Project three corners of the hexagon in the end elevation and note, that the width of the end elevation is given by dimension W.

Line in the projected diameter of the chamfer circle and the base in the front elevation.

As an approximation, draw a radius to show the chamfer on the front elevation. The radius should equal the thread size D.

Add the female convention to the plan view.

Fig. 16.3 Stage 2

Stage 2

1 The projection of the curve on the chamfered faces of the hexagon that lie at an angle would produce ellipses in the front elevation. In their place we usually show small circular arcs, their radii can be found by trial, but are approximately 0.25D.

2 The end elevation of the nut has square corners and the projection of the corner which coincides with the centre line terminates at the bottom of the chamfer curve.

3 Complete the view by drawing circular arcs on the two chamfered faces. Find by trial, the radius of an arc which will touch the top of the nut and the projection lines from the corner in the front elevation.

Reference to Fig. 16.1a and b will show that the constructions in Fig. 16.2 and Fig. 16.3 can be used for the bolthead and locknut where proportions for thickness can be approximated to 0.7D and 0.5D.

For exact dimensions however, please refer to Table 16.1.

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