Table of Contents
Reading Manufacturing Prints
- Types of Drawings
- Projection
- Perspective
- Parallel
- Orthographic
- Single-View Projections
- Multi-View Projections
- Third-Angle Projection
- First-Angle Projection
- Interpretation
ASME Y14.5-2009 Dimensioning Tolerancing
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Objective of GD&T
- Both numeric tolerances and geometric/shape tolerances are shown on industrial prints
- Envelope Principle
- “Unless otherwise specified, the limits of size of a feature prescribe the extent within which variations of geometric form, as well as size, are allowed. This control applies solely to individual regular features of size as defined in the standard.” (Geometric Dimensioning & Tolerancing (GD&T) Fundamentals by Ray Wheeler, rwheeler@rwoptdesign.com)
Geometric Dimensioning and Tolerancing
- Blueprint Reading Basics, 4th by Gills, Chapter 7 - Geometric Dimensioning and Tolerancing
Introduction
- GD&T is a system of specifying tolerances to control the form, location (datum), and orientation of features
- Bother numeric (e.g. +/-) tolerances and geometric (e.g. perpendicular) tolerances are used on the same drawing
GD&T Symbols
- M - at maximum material condition (MMC) or at maximum material boundary
- L - at least material condition (LMC) or at least material boundary
Basic Dimensions
- Basic dimensions have no tolerances, and they describe the intended geometry of the part. They are enclosed in a box.
Features
- Parts are made up of features. Features can be divided into two classes 1) size and 2) surfaces
Bonus Tolerance
- In some cases, the geometric tolerance given in a feature control frame can actually be made larger during inspection, allowing more variation than the print would seem to indicate.
- The difference between the actual produced size and the material condition
Reference Dimensions
- 1.7.6 Reference Dimensions
- “The method for identifying a reference dimension (or reference data) on drawings is to enclose the dimension (or data) within parentheses. See Figs. 1-19 and 1-20” (ASME Y14.5-2009, p. 13)
Inventor 2018 Annotations and Tolerance Features
- Tolerances in Model
- Benefits - export to STEP version 242 will save the tolerances. This is the future and should be a reality in 2022.
- Cons
- cumbersome, recommend just adding the tolerance to a dimension in the drawing, that is manually draw the dimension instead of doing the Retrieve Dimensions which is messy.
Dimensions
- Sketch Dimensions vs Drawing Dimensions
- How do you add diameter symbols, units, descriptive text to a sketch dimension?
- How do you change the sketch dimension size > Application Options > General tab > Annotation scale
- Can enter mixed-unit formulas in a dimension. 3.25 ft - 1 m + 3 cm + 0.125 in = 23.775 mm (see Autodesk University MA2822: 60 Inventor Tips in 60 Minutes, Tip#38)
- Show Dimensions from the Model Browser Window
Sketch Dimensions
- Arc Length Dimension - when dimensioning an arc, have the right click option to assign a dimension type of radius, diameter or arc length.
- Autodesk Inventor 2014 Help - Create arc in sketch
- Autodesk Inventor 2014 Help - Sketch Dimension Reference
Drawing Dimensions
- Autodesk Inventor 2015 Help - Dimension to a midpoint or intersection
Dimension Isometric Views
- Autodesk Inventor Forums Post - How to dimension to extension or centerlines
Dimension Isometric Views Chamfer
- Inventor gives WRONG dimension when dimensioning a chamfer in an isometric drawing.
Surface Finish
- Texture Characteristics
- machined surface contours can be split into three main components: roughness, waviness, and form
- For most applications, roughness is the only characteristic that is specified on prints
- Roughness
- roughness refers to small scale, closely spaced irregularities caused by the cutting process. Marks produced by cutting tools during machining operations are examples of roughness; lines of this type are commonly called 'tool marks.'
- Waviness
- Waviness has a longer period than roughness and can be caused by any cyclic characteristic of the machine-tool-toolholder combination. Flexure of the workpiece or the tool system is also a cause of waviness. Waviness is at its worst when a critical frequency is reached and chatter occurs.
- Form
- Form errors result from machine characteristics such as slideway variations and from inaccurate tool settings. Form errors can also arise from thermal distortions of the workpiece or the machine during cutting and also inadequate support of the workpiece during cutting.
- Lay
- Cutting tools leave characteristic marks on the surface that may affect the way the surface wears and interacts with mating parts. The general direction of the tooling marks depends on the manufacturing method selected; the general direction may be specified for applications where lay is critical.
- Skewness
- Skewness indicates the degree to which roughness comes from external variation or internal variation. For a contact-bearing application, sharp deep valleys separated by wide flat planes (negative skewness) would perform better than sharp spikes (positive skewness), for the same overall roughness value. A surface with positive skewness would contain spikes that would soon wear off, creating wear debris and damage.
- Specification of Surface Texture
- The surface texture symbol looks like a check mark. This symbol provides a uniform and concise way of specifying surface texture.
- Roughness Height, Ra
- surface texture for English prints is specified in microinches [millionths (0.000001) of an inch]
- surface texture for metric prints is specified in micrometers [thousandths (0.001) of a millimeter]
| Microinches | Micrometers | Typical Uses |
| 250 | 6.3 | Clearance surfaces (stock surfaces or rough machined) |
| 125 | 3.2 | General mating surfaces for parts, sealing surfaces used with soft gaskets |
| 63 | 1.6 | Keyways, milled threads, gear teeth |
| 32 | 0.8 | Slideways, journals, sliding mechanisms |
| 16 | 0.4 | Pistons and cylinder bores, cam lobes, precision gear teeth |
| 8 | 0.2 | Precision heavy-duty rolling surfaces, valve seats |
| 4 | 0.1 | Surfaces of fluid seals, pressure-lubricated bearings |
- Symbol Placement
- Surface symbols are normally located so that they touch the object line for the surface that requires the finish. If this is not practical, the symbol is placed on an extension line. And if this is not practical, the symbol is used with a leader line, as illustrated in Figure 8-8 (p. 236). Both the symbol and the inscriptions are oriented for reading from the title block corner. [Hammers p. 236]
- What does “=” mean
- It is a lay direction symbol. Lay parallel to the plane of projection of the view in which the symbol is used.
- No Symbol
- Not all machine parts require special surface textures. Many parts are used as normally manufactured. If texture symbols are not shown, surfaces produced by normal manufacturing methods are acceptable.
- Surface Treatment
- Surface Coatings
Symbols
Style and Standard Editor
- Ribbon: Manage tab → Style and Standards panel → Styles Editor
- Text → Label Text (ANSI)
- Font: Arial Narrow (default is Tahoma with text height 0.180“)
- Text → Note Text (ANSI)
- Font: Arial Narrow (default is Tahoma with text height 0.120”)
- Note: Dimension → Default (ANSI) → Text tab primary text style is Note Text(ANSI)
- Autodesk Inventor 2019 Help - Style and Standard Editor - Text Style Reference
User Defined Symbols
- Autodesk Inventor 2015 Help - Sketched symbols
- “You can create sketched symbols in a drawing or a drawing template. Symbols created in a drawing are available only in that document, but symbols created in a template are available to all drawings based on that template.”
- “Sketched symbols with a leader attached to a model are associated with model properties. If a leader is deleted, the symbol loses its model association, but restoring the leader can recreate the association. Instead of deleting a leader, consider turning off its visibility. Invisible leaders retain symbol association with model properties.”
Special Characters
- Windows → Run → CHARMAP
- (alternate) Windows Accessories → Character Map
- Use Autodesk Inventor Geometric Dimensioning and Tolerancing (AIGDT) font
- Autodesk Inventor 2019 Help - To Add Special Characters to Text or Prompted Entries
References
- [Hammers] Hammer's Blueprint Reading Basics, 4th Ed by Charles A. Gillis
