CAE pt. 1

Mechanical Engineering Drawings

sketch

principal dimensions shown

no tolerances

no drawing or revision number

no “drawn by“ or “approved by“

detail drawing

all dimensions shown

formatted title block: drawing and revision number, “drawn by“, “approved by“

standard drawings (inches) A-E

multiview

three orthogonal views

isometric view

corners at 120 degrees, 30 degrees from flat surface

dimetric view

corners at 150 degrees, 15 degrees from flat surface

trimetric view

front corner at 105, right corner at 135, top corner at 120

left side 15 degrees from bottom, right side 45 degrees from bottom

ANSI projection (third angle)

Front view is key view, top view is above fromt view, right view is to the right of the front view, left view is to the left of the front view, bottom view is below the front view

projection symbols

visible line

thick

used to depict visible edges

hidden line

dashed line representing edges of the object that are not visible in that view

section line

thin, continuous diagonal lines used to identify the surfaces of an object that lie on the cutting plane

center line

thin, dashed lines used to indicate the central axes of cricular features or geometries

alternating long and short dashes that extend beyond the edges of the object

dimension and extension lines

dimension lines are thin, continuous lines with arrows or ticks at the ends that include a numerical value indicating the dimension of a feature

extension lines extend from the object’s edge or a central line to the dimension line

cutting plane or viewing plane lines

thick, dashed lines with arrows on the end (showing line of sight) used to descrive where a section is cut through an object and the direction of sight.

phantom line

thin, dashed lines that indicate the range or extent of motion of a moving feature

dimensioning rules (6)

1. each dimension should be given clearly, so that it can be interpreted in only one way

2. dimensions should not be duplicated, and no dimensions should be given except those needed to produce or inspect the part

3. dimensions should be given between points that have a functional relation to each other or that control the location of mating parts

4. avoid dimensioning hidden lines whenever possible

5. the longer dimensions should be placed outside all intermediate dimensions so that dimension lines will not corss extension lines

6. do not expect workman to assume a feature is centered, but give a location dimension from one side

tolerance

the permissible limit of variatuon in a physical dimension. certain tolerances are requires by engineering standards, especially between mating components

hole based system

size of hole is kept constant, shaft size is varied to get different fits

shaft based system

size of shaft is kept constant, hole size is varied to get different fits

close sliding fit

RC1: accurate location of parts that must assemble without perceptible play

sliding fit

RC2: parts that will move and turn easily but are not intended to run freely

precision running

RC3: precision parts operating at slow speeds and light loads that must run freely

close running fit

RC4: accurate location with minimum play for use under moderate loads and speeds

medium running fit 1

RC5: accurate machine parts for higher speeds and/or loads

medium running 2

RC6: rimilar to RC5 for applications in which larger clearances are required

free running fit

RC7: reliable relative motion under wide temperature variations in which accuracy is not critical

loose running fit 1

RC8: permits large clearances, allowing the use of parts with commercial, “as recieved“ tolerances

losse running fit 2

RC9: similar to RC8 with approximately 50% larger clearances

interference fits

the inside member is larger than the outside member, requiring the application of force during assembly

forcce and shrink fits

limit dimesnioning

upper and lower limits (small difference)

plus and minus dimensioning

base dimension with a plus and minus

single limit dimensioning

min or max to one dimension

required in title block

• drawing name

• drawn by

• name and handwritten initials

• date

• drawing number

• required in drawing, not necessarily in title block

  • unit system

  • scale

detail drawings

exact drawing that provides all the dimensions, tolerances, materials, and manufacturing instructions needed to fabricate a single component

production drawing

official document that gives exact instructions on how to build, measure, and inspect a part

assembly drawings

technical illustration that shows how multiple individual parts fit and dunction together to form a complete product or subassembly

bill of materials

needed for assembly drawings

numbered parts (standard and purchased)

standard part

a part whose dimensions, material, and properties are completely specified in an international or national standard

purchased part

made by an original equipment manufacturer (OEM), usually following national or international manufacturing association standards or guidelines

standard part

the designation of these parts is specified in the standard

they are not designated by a vendor’s part number

ex. bolts, screws, rivets, pins, washers, etc

part drawings

standard parts do not require detail drawings unless modified, and do not require a technical specification sheet

purchased parts do not require detail drawings, but do require a technical specification sheet