Slide 1: Engineering Drawing Notes
Part B – Coordinate Dimensioning & Tolerancing ME170
Computer Aided Design Instructor:
Associate Professor of
Mechanical & Industrial Engineering Contents : Contents 2D Drawing Principles:
Coordinate Dimensioning & Tolerancing
ANSI/ISO Tolerance Designation
ANSI/ISO Classification of Limits and Fits
Economics of Tolerances/Surface properties
Geometric Dimensioning and Tolerancing (GD&T) Attention to Detail
The engineering drawing is the specification for the component or assembly and is an important contractual document with many legal implications, every line and every comment is important. Part A Part B Part C Coordinate Dimensioning and Tolerancing : Coordinate Dimensioning and Tolerancing The collective process of modeling, defining and describing geometric sizes and feature relationships, and providing all of the required technical information necessary to produce and inspect the part is called dimensioning and tolerancing.
The current National Standard for dimensioning and tolerancing in the United States is ASME Y14.5M - 1994. DRAWN IN ACCORDANCE WITH ASME Y14.5M - 1994
REMOVE ALL BURRS AND SHARP EDGES
ALL FILLETS AND ROUNDS R .06 UNLESS OTHERWISE SPECIFIED Drawing Notes : Drawing Notes DRAWN IN ACCORDANCE WITH ASME Y14.5M - 1994
REMOVE ALL BURRS AND SHARP EDGES
ALL FILLETS AND ROUNDS R .06 UNLESS OTHERWISE SPECIFIED Notes should be concise and specific. They should use appropriate technical language, and be complete and accurate in every detail. They should be authored in such a way as to have only one possible interpretation. General Notes Local Notes 4X 8.20 M10 X 1.25
82º CSK 10
1.5 X 45º CHAM Line Types : Line Types Object Lines
Cutting Plane Line
Sections - Hatching
Break Lines thin thin thin thick thin thin thick thick Arrowheads : Arrowheads Arrowheads are used as terminators on dimension lines. The points of the arrowheads on leader lines and dimension lines must make contact with the feature object line or extension lines which represent the feature being dimensioned. The standard size ratio for all arrowheads on mechanical drawings is 3:1 (length to width). 1st 2nd 3rd 4th Of the four different arrowhead types that are authorized by the national standard, ASME Y14.2M – 1994, a filled arrowhead is the highest preference. Slide 7: Dimensions should be placed outside the actual part outline. Dimensions should not be placed within the part boundaries unless greater clarity would result. There should be a
visible gap (~1.5 mm)
between the object lines
and the beginning of
each extension line. Extension lines overlap dimension lines (beyond the point of the arrowheads) by a distance of roughly 2-3mm 1.75 1.06 Dimension Lines and Extension Lines Slide 8: Arrows in / dimension in Arrows out / dimension in Arrows in / dimension out Arrows out / dimension out 2.562 1.250 .750 .500 Placement of Linear DimensionsOrder of Preference When there is not enough room between the extension lines to accommodate either the dimension value or the dimension lines they can be placed outside the extension lines as shown in the fourth example (use Flip Arrows in ProE). Slide 9: Reference Dimension Symbol (X.XXX) Reference dimensions are used on drawings to provide support information only.
They are values that have been derived from other dimensions and therefore should not be used for calculation, production or inspection of parts.
The use of reference dimensions on drawings should be minimized. EXAMPLE 2.250 1.000 (.750) .500 1.250 .500 (.750) .500 Reference Dimensions Slide 10: 4.375 1.250 1.438 1.062 .688 1.000 1.875 2.312 .375 (10mm)
Minimum Spacing .250 (6mm)
Minimum Spacing Shorter (intermediate) dimensions are placed closest to the outline of the part, followed by dimensions of greater length. Dimensions nearest the object outline should be at least .375 inches (10 mm) away from the object, and succeeding parallel dimension lines should be at least .250 inches (6 mm) apart. Location of Dimensions Dimensions should be placed outside the actual part outline Slide 11: 4.375 1.062 .688 1.000 1.875 2.312 1.250 1.438 4.375 1.062 .688 1.000 2.312 1.250 1.438 Extension lines should not cross dimension lines if avoidable BETTER Basic Dimensioning – Good Practice In-line dimensions can share arrowheads with contiguous dimensions 1.875 Slide 12: 1.375 1.375 .625 THRU .250 .62 .250
x .62 DP Diameter Dimensions
Holes and cutouts Slide 13: Whenever it is practical to do so, external diameters are dimensioned in rectangular (or longitudinal) views. Cylindrical holes, slotted holes, and cutouts that are irregular in shape would normally be dimensioned in views where their true geometric shape is shown. Diameter Dimensions
Shafts and Holes Slide 14: 18º 18º 18º 18º 18º 18º 3.50 .875 3X .562 6X .188 Placement with Polar CoordinatesTo dimension features on a round or axisymmetric component Slide 15: Radial Dimensions
To indicate the size of fillets, rounds, and radii R.562 R.750 R.312 R.312 R14.25 : Angular Dimensions:
To indicate the size of angular details appearing as either angular or linear dimensions. 92º 2 x 45º 63º Alternate “Times” and “By” Symbol: X : “Times” and “By” Symbol: X The X symbol can also be used to indicate the word “by”. For instance, when a slot that has a given width by a specified length, or a chamfer that has equal sides (.12 X .12).
When used to imply the word ‘by’, a space must precede and follow the X symbol.
If the same feature is repeated on the drawing (such as 8 holes of the same diameter and in a specified pattern), the number of times the instruction applies is called out using the symbol X. .12 X 45º
.562 X 82º CSK : Normally specified by diameter and depth (or THRU note used). Specify reaming if accuracy/finish is important. Drilled Holes 25 90 12.5 2x 12 THRU 12 12.5 14 THRU 12 45 25 90 50 32 ASME/ANSI Hole Depth Symbol : Depth or Deep Symbol* * This symbol is currently not used in the ISO standard. It has been proposed. .375
.625 EXAMPLE .375 .625 OR ASME/ANSI Hole Depth Symbol Features such as blind holes and counterbores, must have a depth called out to fully describe their geometry. ASME/ANSI Countersink Symbol : Countersink Symbol* ASME/ANSI Countersink Symbol The symbol denotes a requirement for countersunk holes used to recess flathead screws. The height of the symbol is equal to the letter height on the drawing, and the included angle is drawn at 90º. Note that this symbol is not used in the ISO (international) standard. * This symbol is currently not used in the ISO standard. It has been proposed. EXAMPLE ASME/ANSI Counterbore Symbol : Counterbore Symbol* This symbol denotes counterbored holes used to recess machine screw heads. * This symbol is currently not used in the ISO standard. It has been proposed. EXAMPLE .562 .312 .375 OR ASME/ANSI Counterbore Symbol Slide 22: Counterbores and Countersinks – ISO Standard Flat Head Socket Cap Head or
Machine screws 2 x 8.8 THRU 14 C BORE x 8.2 DP 12 2 x 8.8 THRU 15 CSK 12 50 25 90 12.5 32 50 25 90 12.5 32 : ISO specify metric only: Note: Use standard screw sizes only M 16 x 2 - 4h - 5H ISO metric
Pitch(mm) Class of fit
of this thread
(optional) Class of fit
of mating thread (optional) American Unified Threads: 3/4 - 10 - UNC - 2A Nominal
per inch Class of fit (optional) Thread Series
UNC = Unified Coarse
UNF = Unified Fine Thread Type (optional)
B=Internal Screw Threads M 16 x 2 3/4 - 10 - UNC Slide 24: Threads and Screw Fastening Example
Assembly Slide 25: Threads and Screw Fastening (cont.) Base
Detail : Threads and Screw Fastening (cont.) Lid
Detail 'A' 'A' Section 'A'-'A' 3 Holes 12.7 THRU EQ SP on 120 PD Tolerancesimportant to interchangeability and provision for replacement parts : Tolerancesimportant to interchangeability and provision for replacement parts It is impossible to make parts to an exact size. The tolerance, or accuracy required, will depend on the function of the part and the particular feature being dimensioned. Therefore, the range of permissible size, or tolerance, must be specified for all dimensions on a drawing, by the designer/draftsperson.
Nominal Size: is the size used for general identification, not the exact size.
Actual Size: is the measured dimension. A shaft of nominal diameter 10 mm may be measured to be an actual size of 9.975 mm.
In ISO metric, general tolerances are specified in a note, usually in the title block, typically of the form: "General tolerances ±.25 unless otherwise stated".
In English Units , the decimal place indicates the general tolerance given in the title block notes, typically:
Fractions = ±1/16, .X = ±.03, .XX = ±.01, .XXX = ±.005, .XXXX = ±0.0005,
Note: Fractions and this type of general tolerancing is not permissible in ISO metric standards. Slide 28: Specific Tolerances indicate a special situation that cannot be covered by the general tolerance.
Specific tolerances are placed on the drawing with the dimension and have traditionally been expressed in a number of ways: Specific Tolerances 40 +0.05
- 0.03 40.01 +0.04 40.05
39.97 Bilateral Tolerance Unilateral Tolerance Limit Dimensions Limits are the maximum and minimum sizes permitted by the the tolerance. All of the above methods show that the dimension has:
a Lower Limit = 39.97 mm
an Upper Limit = 40.05 mm
a Tolerance = 0.08 mm
Manufacturing must ensure that the dimensions are kept within the limits specified. Design must not over specify as tolerances have an exponential affect on cost. - Limits and Fits : Limits and Fits 1. Clearance Fits
The largest permitted shaft diameter is smaller than the diameter of the smallest hole : 2. Interference Fits
The minimum permitted diameter of the shaft is larger than the maximum diameter of the hole
3. Transition Fits
The diameter of the largest allowable hole is greater than that of the smallest shaft, but the smallest hole is smaller than the largest shaft Standard Limits and Fits -- ANSI : Standard Limits and Fits -- ANSI RC 1 Close sliding fits are intended for the accurate location of parts which must assemble without perceptible play.
RC 2 Sliding fits are intended for accurate location, but with greater maximum clearance than class RC 1. Parts made to
this fit move and turn easily but are not intended to run freely, and in the larger sizes may seize with small
RC 3 Precision running fits are about the closest fits which can be expected to run freely, and are intended for precision
work at slow speeds and light journal pressures, but are not suitable where appreciable temperature differences
are likely to be encountered.
RC 4 Close running fits are intended chiefly for running fits on accurate machinery with moderate surface speeds and
journal pressures, where accurate location and minimum play are desired.
Basic hole system. Limits are in thousandths of an inch. Class RC 1 Limits of
g4 Class RC 2 Limits of
g5 Class RC 3 Limits of
f6 Class RC 4 Limits of
f7 Class RC 5 Limits of
e7 Class RC 6 Limits of
e8 Medium running fits are intended for higher running speeds, or heavy journal pressures, or both. Nominal
Inches 0 - 0.12 0.1 + 0.2 - 0.1 0.1 + 0.25 - 0.1 0.3 + 0.4 - 0.3 0.3 + 0.6 - 0.3 0.6 + 0.6 - 0.6 0.6 + 1.0 - 0.6
0.45 - 0 - 0.25 0.55 - 0 - 0.3 0.95 - 0 - 0.55 1.3 - 0 - 0.7 1.6 - 0 - 1.0 2.2 - 0 - 1.2
0.12 - 0.24 0.15 + 0.2 - 0.15 0.15 + 0.3 - 0.15 0.4 + 0.5 - 0.4 0.4 + 0.7 - 0.4 0.8 + 0.7 - 0.8 0.8 + 1.2 - 0.8
0.5 - 0 - 0.3 0.65 - 0 - 0.35 1.12 - 0 - 0.7 1.6 - 0 - 0.9 2.0 - 0 - 1.3 2.7 - 0 - 1.5
0.24 - 0.40 0.2 + 0.25 - 0.2 0.2 + 0.4 - 0.2 0.5 + 0.6 - 0.5 0.5 + 0.9 - 0.5 1.0 + 0.9 - 1.0 1.0 + 1.4 - 1.0
0.6 - 0 - 0.35 0.85 - 0 - 0.45 1.5 - 0 - 0.9 2.0 - 0 - 1.1 2.5 - 0 - 1.6 3.3 - 0 - 1.9
0.40 - 0.71 0.25 + 0.3 - 0.25 0.25 + 0.4 - 0.25 0.6 + 0.7 - 0.6 0.6 + 1.0 - 0.6 1.2 + 1.0 - 1.2 1.2 + 1.6 - 1.2
0.75 - 0 - 0.45 0.95 - 0 - 0.55 1.7 - 0 - 1.0 2.3 - 0 - 1.3 2.9 - 0 - 1.9 3.8 - 0 - 2.2
0.71 - 1.19 0.3 + 0.4 - 0.3 0.3 + 0.5 - 0.3 0.8 + 0.8 - 0.8 0.8 + 1.2 - 0.8 1.6 + 1.2 - 1.6 1.6 + 2.0 - 1.6
0.95 - 0 - 0.55 1.2 - 0 - 0.7 2.1 - 0 - 1.3 2.8 - 0 - 1.6 3.6 - 0 - 2.4 4.8 - 0 - 2.8
1.19 - 1.97
1.97 - 3.15 Extract from Table of Clearance Fits ISO Tolerance Designation : ISO Tolerance Designation The ISO system provides for:
21 types of holes (standard tolerances) designated by uppercase letters A, B, C, D, E....etc. and
21 types of shafts designated by the lower case letters a, b, c, d, e...etc. These letters define the position of the tolerance zone relative to the nominal size. To each of these types of hole or shaft are applied 16 grades of tolerance, designated by numbers IT1 to IT16 - the "Fundamental Tolerances":
ITn = (0.45 x 3 D +0.001 D) Pn
where D is the mean of the range of diameters and Pn is the progression:1, 1.6, 2.5, 4.0, 6.0, 10, 16, 25......etc. which makes each tolerance grade approximately 60% of its predecessor. For Example: : For Example: Experience has shown that the dimensional accuracy of manufactured parts is approximately proportional to the cube root of the size of the part.
A hole is specified as: 30 H7
The H class of holes has limits of . i.e. all tolerances start at the nominal size and go positive by the amount designated by the IT number.
IT7 for diameters ranging 30- 50 mm: + x
+ 0 Tolerance for IT7 = (0.45 x 3 40 +0.001x 40) 16 = 0.025 mm Written on a drawing as 30 H7 Slide 34: Graphical illustration of ISO standard fits Hole Series – H hole Standard Selection of Fits and theISO Hole Basis system : Selection of Fits and theISO Hole Basis system From the above it will be realized that there are a very large number of combinations of hole deviation and tolerance with shaft deviation and tolerance. However, a given manufacturing organization will require a number of different types of fit ranging from tight drive fits to light running fits for bearings etc. Such a series of fits may be obtained using one of two standard systems:
The Shaft Basis System:
For a given nominal size a series of fits is arranged for a given nominal size using a standard shaft and varying the limits on the hole.
The Hole Basis System:
For a given nominal size, the limits on the hole are kept constant, and a series of fits are obtained by only varying the limits on the shaft.
The HOLE SYSTEM is commonly used because holes are more difficult to produce to a given size and are more difficult to inspect. The H series (lower limit at nominal, 0.00) is typically used and standard tooling (e.g. H7 reamers) and gauges are common for this standard. ISO Standard "Hole Basis" Clearance Fits : ISO Standard "Hole Basis" Clearance Fits Type of Fit Hole Shaft Loose Running Fits . Suitable for loose pulleys and the looser fastener fits where freedom of assembly is of prime importance H11 c11 Free Running Fit. Where accuracy is not essential, but good for large temperature variation, high running speeds, heavy journal pressures H9 d10 Close Running Fit. Suitable for lubricated bearing, greater accuracy, accurate location, where no substantial temperature difference is encountered. H8 f7 Sliding Fits . Suitable for precision location fits. Shafts are expensive to manufacture since the clearances are small and they are not recommended for running fits except in precision equipment where the shaft loadings are very light. H7 g6 Locational Clearance Fits . Provides snug fit for locating stationary parts; but can be freely assembled and disassembled. H7 h6 : ISO Standard "Hole Basis”
Transition Fits Type of Fit Locational Transition Fits . for accurate location, a compromise between clearance and interference Push Fits . Transition fits averaging little or no clearance and are recommended for location fits where a slight interferance can be tolerated for the purpose, for example, of eliminating vibration. Hole Shaft H7 k6 H7 n6 ISO Standard "Hole Basis"
Interference Fits Type of Fit Press Fit . Suitable as the standard press fit into ferrous, i.e. steel, cast iron etc., assemblies. Drive Fit Suitable as press fits in material of low modulus of elasticity such as light alloys. Hole Shaft H7 p6 H7 s6 : ISO Clearance Fits : ISO
Fits : ISO
Fits Slide 41: Flanged Sintered Bronze Plain Bearing Slide 43: http://www.McMasterCarr.com Slide 44: On-line Interactive Catalogs http://www.skf.com/portal/skf/home/products?maincatalogue=1&lang=en&newlink=1 Slide 45: Tolerance Calculation - 'Worst Case Method' for correct fit in all cases, if manufactured to specification Slide 46: Shaft in Hole Example Lid on Box Example 1. Allowance = Smallest Hole Size (A) – Largest Shaft Size (B) 2. Clearance = Largest Hole Size (A) – Smallest Shaft Size (B) A A B B Worst Case Tolerancing Slide 47: Tolerance Calculation - Tensioner Assy. Example <0.25 1. Allowance = Smallest Hole Size (76.16) – Largest Shaft Size (76.15) = 0.01 2. Clearance = Largest Hole Size (76.25) – Smallest Shaft Size (76.00) = 0.25 Worst Case Tolerancing: Axial Clearance by Design must be
=> 0.01 but =< 0.25 Slide 48: Basic Surface Texture Symbol With Roughness Value
(Typically Ra µm or µ”) 0.4 Material Removal by Machining With Machining Allowance 2 Harden = HDN - may see symbol
Heat Treat = H/T
Rockwell = HRC, HRA etc or Ra or Rc
Brinell = BNL Hardness Surface Finish HDN to 65 HRC 0.125 DP 0.4 Surface Properties -
Texture and Hardness Slide 49: Comparative Roughness Values Roughness Ra Typical Processes
25 µm (1000 µ”) Flame Cutting
12.5 µm (500µ”) Sawing, sand casting,
6.3 µm (250µ”) forging, shaping, planing
3.2 µm (125µ”) Rough machining, milling, rough turning, drilling, and die casting
1.6 µm (63µ”) Machining, turning, milling, die and investment casting, injection molding, and stamping
0.8 µm (32µ”) Grinding, fine turning & milling, reaming, honing, injection molding, stamping, investment casting
0.4 µm (16µ”) Diamond Turning, Grinding, lapping, honing
0.2 µm (8µ”) Lapping, honing, polishing
0.1 µm (4µ”) Superfinishing, polishing, lapping Slide 50: Some Common Steel, Hardness and Surface Finish Specs. Common Steel Specs: (10xx series: xx = % carbon)
Mild steel (low carbon = up to 30 %): Low cost general purpose applications, typ. hardening not required
Medium Carbon (up to 60%): requiring higher strength; e.g. gears, axles, con-rods etc.
High Carbon (> 60%): High wear, high strength; e.g. cutting tools, springs etc.
Ground Bearing Shaft Examples:
1060: Surface HDN to 55 HRC 0.125 mm deep min.; 0.4 µm (16 µ”)
303 Stainless: (natural surface hardness 5 HRC ); 0.4µm (16 µ”)
Better Finish, Longer Life
1020: Case HDN to 65 HRC 0.25 mm deep min.; 0.2µm (8 µ”)
440 Stainless: (natural circa 15 HRC); 0.2µm (8 µ”) 1020 1040,
1060 1080 Common
Types Slide 51: Specifying Welds on Drawings Width of weld