MECH 1800 - Interpreting Engineering Drawings PDF

Koorosh Nikfetrat No extensions & makeup grades CLASS 1 - SEP 5 Two Types of Technical Drawings 1.​ Pictorial a.​ Isometric - lines stay parallel b.​ Perspective - has vanishing points c.​ Oblique 2.​ Orthographic Projectio...

Koorosh Nikfetrat No extensions & makeup grades CLASS 1 - SEP 5 Two Types of Technical Drawings 1.​ Pictorial a.​ Isometric - lines stay parallel b.​ Perspective - has vanishing points c.​ Oblique 2.​ Orthographic Projections - top, front, and side view; like packaging design CLASS 2 - SEP 12 Two Ways to Project a View: -​ Third angle projection used mostly in North America -​ Paper is between the object and viewer -​ Light leaving the object towards viewer and the light getting intercepted by paper -​ First angle projection used mostly in Asia and Europe -​ Object is between the viewer and paper -​ Light leaving the viewers eyes and the “shadow” of the object falling on the paper behind the object Notes: -​ Construction or auxiliary lines are required to produce a drawing -​ Projections are not only used for drawings of parts, they are also used for display of “scientific data” -​ Specific volume is the inverse of a density CLASS 3 - SEP 19 Dimensioning - instructions that can be used to make parts ​ Indicate the size of parts without ambiguity ​ Implies drawings should be to scale with correct proportions ​ Notes complement size specification ​ Further instructions should not be necessary to make the part Lines used for dimensioning are thinner than the outlines of the object Dimensioning specifies: ​ Distances ​ Diameter/radius ​ Angle ​ Location Dimensioning is indicated by: ​ Extension lines ​ Dimension lines ​ Leaders ​ Arrow heads 3 Rules for Dimensioning 1.​ When possible, place dimension between views 2.​ Place shortest dimension closest to object 3.​ Dimension on the view that best shows the feature Only critical dimensions should be specified, other dimensions are allowed to “fall into place”. -​ Overspecification increases production cost -​ When two or more holes of the same size are required, the number of holes is specified -​ A round, radius, or chamfer is put on the outside of a piece to improve its appearance and to avoid forming a sharp edge that might chip off under a sharp blow or cause injury -​ A fillet is additional material allowed in the inner intersection of two surfaces, to avoid stress concentration and make manufacture easier -​ For rounds and fillets, a general note is normally used instead of individual dimensions (ex. ROUNDS AND FILLETS R10 UNLESS OTHERWISE SHOWN)  CLASS 4 - SEP 26 Applied Geometry 180 Divide the sides Ex. square: 180 / 4 = 45 Make 45 degree angle for first line Next line angle - 90 Drawing Scales ​ Allows a drawing to have the same proportions as the real object ​ Very large and very small objects can fit on almost any size paper and can be printed (warning: details may require exploded views) ​ Usually shown as drawing size: object size (e.g. 1:3) ○​ Interpreted to mean 1 unit on paper represents 3 units in the real world or drawing is ⅓ the real size ○​ Or shown more explicitly in terms of units (e.g. 1 cm: 1 m) ○​ Can also use triangular scale rulers Sectional Views ​ Cross-hatched ​ View of the interior parts of an object that is otherwise difficult or impossible to see ​ Could replace an orthographic projection ​ Sectional view should maintain orientation of cutting line ​ Cutting line can have several segments not in a straight line ​ Standardized section lines are used for “hatching” sectional views ○​ Usually equally spaced parallel lines at 45° (not parallel to any line of the object) ○​ Hatching can be used to differentiate between materials Countersunk & Counterbore Holes and Spotfaces ​ Countersunk hole - has a conical depression to receive a countersunk screw that has a flathead. Flush with surface ​ Counterbore hole - has been machined to a larger ​ Spotface - a surface To convert the explicit scaling into simpler forms, you can express the ratios with the same units for both sides: a. 5 cm: 2000 m Convert meters to centimeters: 2000 m=200,000 cm. The simplified form becomes: 5 cm:200,000 cm Now simplify the ratio: 1:40,000 b. 1 inch: 1 km Convert kilometers to inches (1 km = 39,370.1 inches): 1 km=39,370.1 inches The simplified form becomes: 1 inch:39,370.1 inches So, the ratio is: 1:39,370.11:39,370.1 In summary: ​ a. 1 : 40,000 ​ b. 1 : 39,370.1  OCTOBER 10 3 types of lines used for representing shapes: -​ Visible lines -​ Hidden lines -​ Break lines 3 lines used for dimensioning: -​ Extension lines -​ Dimension lines -​ Leaders Visible lines represent items that are visible in a view -​ Solid, thick lines that clearly stand out on the drawing and define the exterior shape of the object Hidden lines depict items that are not directly visible in a view -​ Consist of short, evenly spaced thin dashes and spaces -​ Lines three times as long as spaces ^ bottom left one has gaps in the hidden/dashed circle lines Practice polygon/hexagon Extension lines, leaders, countersink/counterbore Dimensioning SCREWS AND FASTENERS 1.​ Fasteners - used to connect parts to each other a.​ Permanent (welding, adhesives) b.​ Semi-permanent i.​ Rivets - deforms and seals the installation hole. Then it can only be removed with difficulty after. c.​ Removable (threaded) - can be reused. Parts can be disconnected and reconnected many times. i.​ Threaded fasteners 1.​ Bolts - requires nuts and washers 2.​ Screws - no nuts or washers required 3.​ Studs - headless screws threaded on both ends, require nuts ii.​ Metric threads - defined by their pitch (distance between threads) 1.​ M12 x 2.5 means 12mm outer diameter with a 2.5mm pitch 2.​ 8mm deep hole can accommodate 3 complete turns 3.​ Complete turns are what counts for holding strength calculations. More turns = better iii.​ Imperial threads - defined by thread count (# of threads per inch) 1.​ ½ - 20 means ½ - inch diameter screw with 20 threads per inch Pipe -​ Hollow cylinders -​ Structural material -​ Conveyor of fluid -​ Typically, a tubes is a small diameter thin walled pipe -​ Ducts are conveyors with non-circular cross sections (ex. rectangle) -​ Piping diagrams are schematic diagrams for pipe networks Pipes carry: -​ Water -​ Sewage -​ Industrial fluids -​ Oil and gas -​ Food Pipes can be made from different materials, depending on required strength and application: -​ Steel -​ Copper -​ Brass -​ Cast iron -​ Plastic (popular, but not heat resistant) North America - standard pipe sizes (size is nominal, not exact): -​ A 2” schedule 40-steel pipe has an inner diameter of 2.067” and a wall thickness of 0.154” -​ A 2” schedule 80-steel pipe has an inner diameter of 1.939” and a wall thickness of 0.218” -​ They both have an outside diameter of 2.375” Pipes can be connected in series / parallel, just like electrical circuits -​ Pipe network - set of connected pipes -​ Pipes can be connected directly to each other via joints or fittings -​ Fittings: -​ Expansions & contractions -​ Bends & elbows -​ Junctions (T or cross) -​ Connections: -​ Welded -​ Screwed -​ Flanged Pipe networks include one or more equipment: -​ Pumps or compressors -​ Valves -​ Faucets -​ Boilers and condensers Valves -​ Stop, adjust, or regulate flows of fluids -​ Valve types: -​ Globe valve - high resistance even when open, effective for fast shut off -​ Gate valve - flow rate control -​ Check valve - checks, prevents reverse flow Pumps -​ Move fluid through the pipe network system -​ Positive displacement pumps - for high viscosity fluids or very high pressure applications -​ Kinetic (centrifugal) pumps - for low viscosity and high flow rates Drawing Piping Diagrams -​ Both planar & isometric view drawings can be used to represent piping diagrams -​ Isometric views - recommended if pipes bend in more than 1 direction -​ 2D drawing -​ Single line pipe drawings - uses a single line to show the pipes -​ Standard symbols are used for fittings & components Pipe diagram drawing examples: Sprinkler system drawing: Valve types: -​ Globe valve - uses a diaphragm attached to a stem that moves up and down and closes the flow when pressed against its seat. Valve is externally spherical. -​ Angle valve - globe valve with an inlet and outlet at 90 angle. -​ Ball valve - uses a ball with a hole. If the hole is aligned with the flow, it is wide open. -​ Butterfly valve - quarter turn, suitable for quick on/off operations, not recommended for regulating flow. -​ Gate valve - uses a gate that moves up / down in the down position and fully stops flow. Not intended for regulating flow. Almost no resistance in a fully open position. Piping diagrams 2 representations: -​ Single line drawings -​ Double line drawings -​ Centerline is usually shown. ​ Industrial process can often be explained via piping diagram ​ Dimensions of pipe and pipe fitting always given from centre to centre of pipes and to the outer face if the pipe end or flange ​ Total length of pipe required is usually mentioned in the Bill of the Materials Title Block -​ Located at the bottom right of the drawing -​ Gives details and general info -​ Often preprinted on company drawing paper, or standardized templates for CAD Contour Plot