Chapter 3 - Technical Drawings Flashcards
How does the ability to read and interpret technical drawings benefit a millwright?
- they are needed to understand how a machine is crafted, assembled, and installed.
- allows isolation of a problem area before a system is dismantled
List the types of technical drawings used in industry today.
- orthographic drawings
— first-angle
— third-angle - pictorial drawings
— isometric
— oblique - schematic diagrams
In an orthographic drawing, what direction is the object viewed from in the front elevation and the plan view?
- front elevation, the object is viewed from the front
- plan view, the object is viewed from the top or bottom
Most often, where do first-angle projection and third-angle projection originate?
- first-angle projection is used in Europe
- third-angle projections is used in North America
Describe how first-angle projection differs from third-angle projection.
- first-angle
— viewing position > object > side elevation - third-angle
— viewing position > side elevation > object
Name the views that are usually required in a third-angle orthographic projection drawing.
- top (plan)
- front (front elevation)
- side (side elevation)
- sometime auxiliary and sectional views are needed
Which view is chosen to be the front view for a technical drawing?
- most objects do not have a natural front or side position.
- therefore, it is necessary to determine which side of the object provides the most information about its shape
- this side is used as the front view
What are the merits and limitations of pictorial drawings?
Merits
- 3D renderings of an object showing height, length and width
- help viewer to visualize the true shape of an object
Limitations
- do not describe the shape of an object either exactly or completely
Describe how isometric and oblique drawings are drawn.
Isometric
- all lines are drawn either vertically or at 30 degrees to the horizontal
- the lengths along the 30 degrees axes are drawn to full scale
Oblique
- on face is at right angle to the horizontal and the others are at an angle (usually 45 degrees) to the horizontal
- the receding dimensions along the 45 degrees axis are drawn to half scale
How is line thickness defined by Canadian standards?
- Canadians standards define line thickness as THICK or THIN
- thick lines - twice as thick as thin lines
Draw and describe
- construction lines
- thin lines used to lay out the various views of an object
- construction lines are eventually overpaid by the object lines
Draw and describe
- object lines
- thick lines which indicate the visible outline of an object
Draw and describe
- hidden lines
- show those surfaces and features of the object that are not seen in the chosen views
- they are thin, equally spaced, broken lines
Draw and describe
- break lines
- used to shorten the view of long uniform sections
Draw and describe
- section lines
- the parallel diagonal lines (hatch marks) that identify a sectional view of an object in a drawing
Draw and describe
- centrelines
- drawn as thin, broken lines, with long and short lines spaced alternately
Draw and describe
- cutting plane line
- offset cutting plane lines are usually if the broken type
- letters placed beside arrows key to the corresponding sectional view
Draw and describe
- extension and dimension lines
- Extension lines
— thin lines which extend the object lines out to a convenient space for dimensioning
— these lines do not touch the object lines
— if extension lines cross arrowheads or dimension lines, a break in the extension line is permitted - Dimension lines
— thin lines which indicate the distance between the extension lines. They terminate with arrowheads which touch the extension lines.
— these lines give the objects measured dimensions; height, width and length
— where one or more dimension lines share an extension line, the dimension lines should run parallel to each other
What are the two methods used to dimension objects?
- Aligned method
— all dimension figures except angular dimensions are written parallel to the dimension lines - Unidirectional dimensioning
— all figures are written parallel to the bottom of the drafting paper
What two types of dimensions are found on technical drawings?
- Overall dimensions
— indicate overall length, width, or height of an object - Detail dimensions
— give size and location of any feature or detail which is not overall length, height or width
State the rules for dimensioning technical drawings
- only one form of dimension is used on a single drawing; either aligned or unidirectional
- technical drawings are dimensioned so that the full-size dimensions are specified on he drawing regardless of scale
- in metric drawings, dimensions are shown in millimetres without their units (1100, not 1100mm)
- the position and size of angles are shown
- when metric values are less than one, a zero is shown before the decimal point (0.5, not .5)
- whenever possible, to avoid confusion, dimensions are placed close to features being shown and outside the objects outline
- dimensions of a feature are shown only once
- when space is limited, dimension figures are placed in one or the other way
— inside the dimension line with the arrowheads outside the extension lines
— with the figures and arrowheads outside the extension lines
What are the overall dimensions of the object in figure 11?
-
What is the hole size and the size and depth of the counter-bored hole in figure 13?
-
Where are the holes located in the square plate in figure 14?
-
What is the diameter of the bolt pattern in figure 15?
-
What are the purposes of sectional view?
- used to show an aspect of the object which is otherwise too complicated to show with the conventional top, front, and side views
- show differences in materials
Describe the difference between full-section and half-section views.
Full section - use a cutting plane through the whole object giving the impression that the object has been cut in half
Half section - remove only a certain portion of the drawing. If a half section views gives all the information needed to understand the drawing, hen a full section drawing is not given
Which views are pictorial and which views are orthographic in figure 16?
-
Can section lines identify the material and object is made from?
- line patterns are used to indicate types of materials
- also indicate solid portions of an object
How are offset sectional cutting planes indicated on the drawing in figure 18?
-
Where is the lower bolt hole located in the aligned sectional view in figure 19?
-
How are holes illustrated in a sectional view when the cutting plane line passes through them?
- blank dimensioned without line patterns
How is a removed sectional view identified? Figure 21
- sectional labelling
Describe how the broken-out sectional view in figure 22 helps in the understanding of the object.
- shows X-ray of interior dimensions
What are the reasons for using auxiliary views?
Figure 23
- used to detail sloping (or inclining) surfaces which cannot be depicted in normally orthographic views
- clearly shows the shape of the object and gives its true dimensions
Which of the regular views is the front view in figure 23?
-
Why would and object have two or more auxiliary views?
- occasionally an object cannot be completely described in one auxiliary view, so an additional auxiliary view may be needed
What are the merits of the exploded view in figure 24?
- exploded views take a very complicated drawing and separates it along s common axis where possible
- the viewer sees exactly how a group of parts fit together
Is the exploded view orthographic or pictorial in figure 24?
-
Define tolerance.
- the total permissible/allowable variance of the basic size of a component
- tolerance limits are the maximum and minimum sizes that are allowable
- the tolerance is the difference between the max and min limits
What is the maximum and the minimum material size for the following?
- 28.00 +0 -0.06 mm
- 28.00mm
- 27.94mm
What is the maximum and the minimum material size for the following?
- 33.00 +0.08 - 0 mm
- 33.00mm
- 33.08mm
What is the maximum and the minimum material size for the following?
- 42.50 +- 0.5 mm
- 42.00mm
- 43.00mm
What is the advantage of the direct method of indicating tolerance?
- shows both upper and lower limit together
- eliminates any calculations concerning maximum and minimum tolerances
- not the upper and lower limits are given, and the MMC is given in the upper position
Draw and ISO datum-feature symbol
- [A]-
What is the significance of a datum or reference point?
- when several tolerances are given in a sequence, a datum or reference point should be given
- all dimensions are referenced to this point
What is the maximum tolerable overall length of the part featured in figure 26?
-
Define clearance and interference fits.
- tolerances May be either clearance (positive), or interference (negative) fit
Clearance - one in which the machines pieces can be fitted by hand
Interference - requires heat, cold, or a combination of both to assemble the piece
Draw symbols to indicate the following:
- part must be straight within 0.10mm
- — 0.10
Draw symbols to indicate the following:
- shaft runout must be within 0.8 mm
-↗️🅰️🅱️0.8
State the primary measurements for surface texture
- micrometer (um) — a micrometer is one millionth of a metre (0.000 001 meters)
- micro-inch (uin) — a micro-inch is one millionth of an inch 0.000 001 inch)
What would be a typical application for a drilled hole with a finish between N8 and N7?
Table 1
- good for close fits
- unsuitable for fast rotating members
List the information blocks used on technical drawings to relay information.
- zone numbers
- title block
- revision block
- materials list
- scale
What is the purpose of zone numbers and letters?
- refer to certain areas on the print in much the same fashion as coordinate numbers on a map
Where is the title block located on a technical drawing and what information does it contain?
- should always appear in the lower right-side of the printed
- contains information as the — drawing number, title or description of the part, the name of the firm that prepared the drawing, and the scale, as well as any other provisions made
Where is a revision block located and what information does it contain?
- may be placed either in the lower left- or upper right-hand sides of the print
- lists any and all revisions made to the drawing after the initial drafting of the print
What revision was made on Feb.24/96 by G. Burns to the drawing in figure 34?
-chamfer added
Where is the materials list located on the technical drawing and what does it contain?
- generally located just above the title block
- if there is no revision black in the upper right-hand, then the material list is placed here
- May also be called the item list
- all parts in a materials list are identified by their part or stock number
- provides for the number and size of each of part including all fasteners, such as bolts, washers and nuts
How long will the drawing of a part be if the part is 980mm long and it is drawn to a scale of 1:5?
- 5X smaller than actual size
- 196mm
What information does a detail drawing contain?
- a description of the shape
- all necessary views and lines needed to describe the complete form of the object
- all dimensions and numerals including tolerances used to specify the object
- general notes, including such thing s ax the materials list, any heat treating, machining, and surface texture
Is the drawing first-angle or third-angle projection in figure 35?
-
What materials are the following items made of in figure 35?:
- #1 the hook?
- steel
What materials are the following items made of in figure 35?:
- #5 the bushing?
- bronze
What materials are the following items made of in figure 35?:
- #8 the locking pin?
- steel
What is the measurement between centres of the hook and the clevis pin in figure 35?
-
What size is the throat opening in the hook in figure 35?
-
What information does and assembly drawing contain?
- an assembly drawing shows the various pieces of a machine and the way they fit together as a complete unit
- used to show the correct working relationship of the mating pieces and their functions
What information does schematic diagrams communicate to the reader?
- facilitates he tracing of hydraulic, pneumatic, or electrical lines and components of each
- shows relationship between various parts of a system
- shows connections, functions and flows
What information is not communicated to the reader of schematic diagrams?
- does not show the actual size, shape, or location of the components or devices within the system
What is the pressure for the hydraulic system in figure 36?
-600 PSI
What information is communicated to the reader of pipe drawings?
- shows functions, connections, flow, and spatial location
Which views are the plan view, the elevation view and the side view in figure 39b?
-
Compare single-line to double-line pipe drawings.
- single line — abstract symbols
- double line — pictorial schematic
What institutions publish symbols for welding, piping, surface texture, and electrical elements?
- ISO — international standards organization
- CSA — Canadian standards association
- ANSI — American national standards institute
