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Fundamentals of mechanical drawing and mechanical fabrication. ECE 156 Matthew Kay. Fundamentals of mechanical drawing. Represent a 3d object in 2d. Show a scaled representation of an object. Unambiguously capture all geometric features of an object.
Giant crossbow by Leonardo da Vinci. His ideas have survived 500 years through his detailed sketches.
Orthographic projection: Multiple views of an object from points of view rotated about the object's center through increments of 90°. The views are positioned relative to each other.
Isometric projection: One view of an object in which the three axes of space (x,y,z) appear equally foreshortened.
Orthographic projection can provide six planar views of an object.Show multiple views to convey every detail.
Center lines are short+long dashed
are short dashed
Orthographic projection: each view can be thought of as projections of an object onto the sides of a glass box.
Nice isometric sketches work well.
Isometric projection with dimensions.
A thin line is used for hatching, leader lines, short centre lines, dimensions and projections.
Dashed lines are used to show hidden edges and important hidden detail, for example wall thickness and holes.
Thin chain lines indicate center lines. Center lines are used to identify the center of a circle, cylindrical features, or a line of symmetry.Line types
Section views are indicated by the direction of arrows.
Anatomy of a dimension
Dimension tolerances are important! Small or “tight” tolerances are expensive. Overall tolerances should typically be specified.
One MIL is one thousandth of an inch.
1 MIL=1/1000 inch=0.001 inch=1x10-3 inch
1 MIL=0.0254mm=25.4 microns
Solid block with a thru-hole
Create a mental picture of the final product.
Determine overall dimensions. Sketch an isometric view.
Mechanical Drawing (1932) by Irene Rice Pereira
List each part required (bolts, nuts, brackets, bearings, hinges, motors, etc).
Determine which parts can be purchased off-the-shelf. (Hint: as many as possible!) List them in a table that indicates the vendor, vendor part #, description (size, thread type, etc), quantity needed, and price.
HINT: Sketch the orthographic views of each part on paper before drawing them with CAD software.
Sometimes good sketches make fine assembly drawings.
Another example of an assembly drawing created by an ECE158 student (AutoCAD).
Illustration of the mechanomyogram sensor showing the two accelerometers and lead wire innervations.
Remember: Anyone should be able to build your device using your fabrication plan …. even 500 years in the future!Questions?
Flying machine by Leonardo da Vinci.