Page 184 - Engineering drawing from first principles using AutoCAD

i Fastening."; 177

Table 8.2 Dimensional details of thick and thin washers

A B C D

M1.6 1.7 4.0 0.3
M2 2.2 5.0 0.3
M2.5 2.7 6.5 0.5
M3 3.2 7.0 0.5
M4 4.3 9.0 0.8
M5 5.3 10.0 1.0
M6 6.4 12.5 1.6 0.8
M8 8.4 17 1.6 1.0
M10 10.5 21 2.0 2.5
M12 13.0 24 2.5 1.6
M16 17.0 30 3.0 2.0
M20 21.0 37 3.0 2.0
M24 25.0 44 4.0 2.5
M30 31.0 56 4.0 2.5
M36 37.0 66 5.0 3.0

Notes
A, washer inside diameter; B, washer outside diameter; C, washer thickness Form A; D, washer thickness
Form B.

diameters of the thread. The outside circle has a small break in the circumference. The
plan view of a male thread, for example of a bolt, is shown by circles representing the
major and minor diameters but the inside circle has a small break in the circumference.
The thread form is shown by parallel lines representing the major and minor diameters.
In sectional views where threads are drawn in engagement, it is not the custom to cross-
hatch between the parallel lines. Empty threads are cross-hatched to the minor diameter
and examples of these conditions are given. The profile at the top of a nut is due to the
manufacturing process of chamfering the corners. Locknuts are roughly half the thick-
ness of full nuts and are often chamfered on both sides. A bolthead is also chamfered but
its thickness is less than that of a nut with the same screw thread. For exact dimensions
refer to the appropriate standard tables.

Stud assembly in tapped hole
The following notes relate to the assembly drawing in Fig. 8.5.

• Only the outside views of nuts, washers and studs are drawn in sectional views.
• Where very thin components are used in a sectional view it is customary to block them in
rather than hatch them. The 1mm thick gasket is shown resting on the engine block.
• Note the clearance hole required to assemble the cylinder head above the gasket.
• The stud, shown separately, is screwed into the block for its whole length, so the thread
appears to be flush with the top of the tapped hole.
• The screw thread in the block needs to be deeper than the thread on the stud to provide
clearance.
• The block is drilled to the minor diameter of the thread and clearance for the thread-
forming operation is provided at the bottom of the hole.
• The depth of the hole is measured from the surface to the bottom of the parallel portion.
After the drilling operation, the drill also leaves a conical part at the bottom of the hole
with an included angle of 120°.
• Hatching does not cover the area where threads are engaged.