Dimensioning And Detailing Your Parts, A Lets Build Resource

This is a follow up on the designing machined parts post. The drawings that I did are for examples and not to be taken as the proper practice for doing drawing.

https://theartsmechanical.wordpress.com/2016/05/31/designing-machined-parts-a-lets-build-resource/

I’m going to start off with this image.

This is a drawing sent to a jobshop in England(http://www.wilsontools.co.uk/) that I ran into on Linked in  and as far as simple goes, it has just about everything needed to make a simple part like this. Well almost, there are a couple of missing dimensions and there needs to be a material and expected finish.  But something like this will get the job done.

I copied the part into Solidworks to show how the next stages of drawing sophistication go. here’s the first.

cone

This  is essentially the same drawing with a title block added. The dimensions are pretty much the same.  What the title block adds is the introduction of tolerances, in this case the tolerances as specified in the tolerance block.  Which in many cases can be enough.

One thing about title block tolerances is that they should be considered a catch all for all drawings. Once you enter them into the title block they should never be changed inside the organization.  That will avoid errors created by changing tolerances. If you need different tolerances put them in the dimensions or in a note.

What happens if you need different tolerances? then you can use linear tolerances or Geometric Dimensioning and Tolerancing(GD&T) or some combination.  Just how that is done depends on the practices of the organization creating the document, the vendors and the practices and standards that may be required by a regulating agency.  In my experience, the combination technique prevails for most places, but that may be because most of my work has involved low production.  GD&T is primarily an inspection tool and as the number of parts goes way up, I suspect that the adherence to practice and stadards goes up. Anyway here’s the same part showing various kinds of tolerances and GD&T use.

cone 2

Defining a part can get very complicated, but it always starts like this.  Here’s a guide on the basics of dimensioning parts. From here:
http://rvhs-denyer.com/web-back/cad/units&tasks/led-ch-7-dimensioning/led-ch-7-dimensioning-text.htm

Before an object can be built, complete information about both the size and shape of the object must be available. The exact shape of an object is communicated through orthographic drawings, which are developed following standard drawing practices. The process of adding size information to a drawing is known as dimensioning the drawing. A well dimensioned part will communicate the size and location requirements for each feature.

Communication is the fundamental purpose of dimensions.

 

PARTS OF A DIMENSION

Dimensioning includes measurements, notes and symbols.

Geometrics is the science of specifying and tolerancing the shapes and locations of features on objects. Once the shape of a part is defined with an orthographic drawing, the size information is added in the form of dimensions. Dimensioning a drawing also identifies the tolerance (or accuracy) required for each dimension.

Dimensioning itself is the process of defining the size, form and location of geometric components on a drawing, by using lines, numbers, symbols and notes. If a part is dimensioned properly, then the intent of the designer is clear to both the person making the part and the inspector checking the part. Without dimensions, an object cannot be produced accurately.

Parts are dimensioned based on two primary criteria:

  • Basic size and locations of the features.
  • Details of a part’s construction and for manufacturing.

A fully defined part has three elements: graphics, dimensions, and notations (words)

Dimensioning must follow these primary guidelines:

  • Accuracy: correct values must be given.
  • Clearness: dimensions must be placed in appropriate positions.
  • Completeness: nothing can be left out, and nothing duplicated.
  • Readability: the appropriate line quality and technique must be used for legibility.

Dimensioning rules are very important for drawing standards. Proper dimensioning will help to manufacturers, engineers etc. to get better understanding of the designed parts. If an object is to be manufactured according to the designer’s specifications, the person making the product usually needs more information than that furnished by a scale drawing of its shape.

Dimensions and drawing notes help provide this information. It is important to realize that the main purpose for creating, dimensioning, and noting a drawing is to communicate the size and shape of the product so that the person making the product can do so as easily and accurately as possible.

The most significant and important information needed for assembly must be provided. It is the job of the drafter to define what that information is and to provide it in the clearest and most efficient way.

Dimensions provide the numerical value that define the size and location of the details (geometric features) of an object and give the overall size of the object. A basic dimension is the numerical value defining the theoretically exact size of a feature. A reference dimension is the numerical value enclosed in parentheses provided for information only, and is not used in the fabrication of the part. Notes provide additional information not found in the dimensions.

Reference dimensions should be used very sparingly, and placed inside parentheses. They should also include the abbreviation “REF” by the dimension.

Below is an illustration that shows the primary components of dimensioning technique to be used on technical drawings.

 

GENERAL TYPES OF DIMENSIONS

There are two general types of dimensions are used in drawings. Size dimensions: such as the size of holes and size of features such as widths and thickness. Location dimensions: such as the location of holes, cutouts, etc

Size dimensions:                                                        

  • Horizontal                        
  • Vertical
  • Diameter
  • Radius

 

 

 

 

 

Location and orientation dimensions:

  • Horizontal
  • Vertical
  • Angle

 

Angular dimensions are shown either in decimal degrees or in degrees, minutes and seconds.

DIMENSIONING ANGLES

There are two ways to dimension angles on an object: coordinate method, or the angular method. The coordinate method specifies two location distances of the angle to be formed by a line. The angular method specifies one location distance and the angle.

 

OVERALL DIMENSIONS

Another type of dimension that is not often discussed, yet is still very important to understand, is the overall dimension. Overall dimensions provide the overall object size and tell the manufacturer how large a piece of material to use to make the object.

When dimensioning an object, apply the following steps:

  • To identify the overall dimensions, tell how large the object is overall. Describe the positive mass. Provide the overall width, height, and depth dimensions.
  • To identify the location dimensions, tell where the features of the object are. Locate the negative masses.
  • To identify the size dimensions, tell how large the features (negative masses) are.

 

NOTES

Notes on a drawing provide added data and information not found in the views which are needed for the part to be completed. Notes should be read first before studying the views of the parts because they may advise you of certain requirements regarding the part.

There are two basic types of notes used in technical drawing: Local Notes, and General Notes.

General notes refer to the drawing as a whole. General notes can be located anywhere in the drawing. However, many companies have their own standards about where the notes must be located – so anyone using the drawings know exactly where to look for them. Often, general notes are located in the upper left corner of a drawing.

Examples of General notes:

  • FINISH ALL OVER
  • FILLETS & ROUNDS R.125

Local notes are pointed to a specific feature with a leader attached.

Examples of Local Notes:

  • 2 X Ø.25
  • .125 X 45° CHAMFER

All notes should be 1/8″ tall letters.

Notes should be brief. They should be carefully worded as to permit only one interpretation. The wording and form of such notes are fairly well standardized. The standards should be carefully followed. Notes should always be lettered horizontally on the sheet.

Always attach leaders at the front of the word of a local note, or after the last word. Never attach them to any other part of a note.

 

REMEMBER:

  • Remember that the dimensions are at least as important as the views of the object.
  • Being correct and accurate is absolutely necessary.
  • Give the dimensions you want the workers to use in making the part!

A simple procedure for laying out the dimensions of a part is to break the part down into a series of geometric features, apply dimensions to size each of the features, then apply dimensions to control the location of the features. There are usually several different ways to dimension any given object. Dimensions should be selected based on the function of the part. Make sure that you directly control the most important features from a functional viewpoint. The dimensions that are selected for describing the part can have a significant impact on the way in which an object is manufactured.

ADDITIONAL RESOURCE

7.1-2 Standards

To be able to dimension drawings so that all people can understand them, standards must be followed by every company in the world. There are different standards in different countries and in some organizations.

Standards are created by these organizations:

  • ASME: American Society of Mechanical Engineers. The leading international developer of codes and standards associated with the art, science, and practice of mechanical engineering

  • ANSI: American National Standards Institute. This institute creates the engineering standards for North America.

  • ISO: International Organization for Standardization. This is a world wide organization that creates engineering standards with approximately 100 participating countries.

  • DIN: Deutsches Institut für Normung. The German Standards Institute created many standards used world wide such as the standards for camera film.

  • JIS: Japanese Industrial Standard. Created after WWI for Japanese standards

  • CEN: European Standards Organization. A non-profit organization whose mission is to foster the European economy in global trading, the welfare of European citizens and the environment by providing an efficient infrastructure to interested parties for the development, maintenance and distribution of coherent sets of standards and specifications.

  • The United States military has two organizations that develop standards: DOD: Department of Defense, and MIL: Military Standard.

In the US, the ones drafters most commonly work with are ASME, ANSI, and ISO.

 

7.1-3 Systems of Measurement Used In Dimensions

Dimensions on drawings are made in US Customary or SI Metric units. Dimensions are placed on drawings using the appropriate units in one of these two systems of measurement.

Sometimes, drawings are dimensioned using both systems (dual dimensioning) so that manufacturers using both systems can use the same drawings. The same number of decimal places should always be used for both dimensions a tolerance dimensioning range.

Here are illustrations of the three basic types of dimensioning systems. They are explained further below

U.S. CUSTOMARY DIMENSIONING

When using the US Customary System, drawings are dimensioned in inches and feet.

The dimensions may be represented in one of two ways. They may be decimal inch dimensions (such as 1.5 or 2.75), or fractional inch dimensions (such as 10 1/2 or 20 3/4).

Drawings based on US Customary system are most commonly dimensioned in decimal inches.

Decimal dimensioning is the standard practice recommended by the ASME drafting standard in mechanical drawing. Decimal inch dimensioning is convenient because decimals are easier to add, subtract, multiply, and divide. Decimal inches are generally used for drawings of objects made from materials such as metal or plastic. These materials can be machined to very fine tolerances. When using decimal-inch dimensioning a zero is not used to the left of the decimal point for values less than one inch.

Fractional inch dimensioning is still widely employed. This type of dimensioning is primarily used in architectural drafting. Yet it is also sometimes used in some engineering drawings. Fractional inch units are often used when making drawings of objects made from materials that typically cannot be machined to very fine tolerances (such as wood).

Dimensions of machine parts are understood to be in in inches.  It is common practice to omit all inch marks on a drawing when all dimensions are expressed in inches, except in situation where this may lead to misinterpretation of dimensions or notes. A one-inch dimension would be shown as 1″ A one inch drill note would be shown as Ø1″ DRILL where Ø is the symbol for diameter.

METRIC DIMENSIONING

ASME standards for metric dimension require all dimensions to be expressed in millimeters (mm). This uses SI Metric units.

There are special rules for dimensioning metric drawings. The millimeter symbol (mm) is not needed in each dimension, but it is used when a dimension is used in a notation. In this case, a single space separates the numeral and the millimeter symbol. Zeros precede the decimal point when the value is less than 1 millimeter: zeroes are not used when the dimension is a whole number. Commas are not used between thousand units. A metric dimensional note should be displayed in or near the title block.

DUAL DIMENSIONING

Working drawings are normally prepared with all US Customary or all Metric dimensions. When the object is to be manufactured using both metric and US Customary measuring systems, a combination of both U.S. and metric dimensions are present. In that case, dual dimensions may be necessary. Dual dimensioning may also be necessary when converting a metric drawing to a US Customary drawing, or vice versa.

When dual dimensions are used, the metric dimensions are placed under the dimension line in parenthesis. Sometimes a metric conversion chart is also used.

 

7.1-4 Dimensioning Conventions

ASME has also standardized the use of lines, numerical values, symbols, notations, and their placement on working drawings. ASME dimensioning standards use dimension lines with arrowheads, dimension numerals, and extension lines.

ASME CONVENTIONS FOR US CUSTOMARY DIMENSIONS

  1. Use the decimal and inch for dimension values (5.75).

  2. Do not use a zero before the decimal point for values less than one inch (.50)

  3. The dimension value is expressed to the same number of decimal places as its tolerance (5.50 ± .002).

  4. The number of decimal places may represent the tolerance.

  • 5.5 = large tolerance

  • 5.50 = average tolerance

  • 5.500 = small tolerance

ASME CONVENTIONS FOR METRIC DIMENSIONS

  1. All dimensions will be in millimeters.

  2. Do not use millimeter symbol mm with dimensions (25 not 25mm).

  3. When a dimension value is less than one millimeter, a zero will precede the decimal point (0.55 not .55).

  4. When the dimension is a whole number, do not use a zero or decimal point (150 not 150.0).

  5. When the dimension uses a decimal value, do not end it with a zero (75.5 not 75.50).

  6. An exception to convention No. 5 is: if the dimension value is followed by a tolerance, the number of decimal places must be equal (75.50 ± 0.05 not 75.5 ± 0.05).

  7. Do not use commas or spaces (1575 not 1,575 or 1 575).

  8. When specifying millimeters of the drawing as in a document, leave a space between the number and the symbol (2585 mm not 2585mm).

  9. Display the word “METRIC” with large lettering near the title block.

  10. Display note example: “UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE MILLIMETERS”

  11. The abbreviation for system international (metric system) is SI.

  • EXAMPLES:

 

 

7.1-5 Dimension Orientation

Dimensions are placed on the drawing in one of two orientations: unidirectional or aligned.

In unidirectional dimensioning, dimensions are always placed horizontally so that they are read from the bottom of the drawing. Unidirectional dimensioning is preferred in many cases.

In aligned dimensioning, dimensions are placed parallel to the dimension line. The numerals are read from either the bottom or from the right side of the drawing. Sometimes a dimension must be lettered to read slightly from the left to align better with the drawing itself. Although it is an accepted practice, it is best to avoid doing this where possible.

Notes such as Ø1/2, should always be lettered horizontally, no matter which convention you are using.

Regardless of the method used, dimensions shown with leaders are lettered parallel to the bottom of the drawing. The same is true for all notes.

This illustration shows examples of both aligned and unidirectional dimensions for comparison.

 

7.1-6 Dimensioning Components

There are basic components that go into dimensioning for technical drawings of any type.

A DIMENSION CONSISTS OF:

  • dimension arrow

  • dimension line

  • dimension value

  • extension lines

NOTES CONSIST OF:

  • leader arrow

  • leader line

    • with a shoulder

  • note description

Refer to the Alphabet of Lines in the next section as a reminder of what these lines look like in relation to other types of lines.

LINEAR DIMENSIONS are comprised of four components as shown in the illustration:

EXTENSION LINES

Extension lines are thin, dark lines which indicate the location on the object’s features that are dimensioned. They indicate which feature is associated with the dimension. They are drawn to the same weight as a centerline, and should be thin enough to contrast with the object lines. The extension lines have a short gap, of about 1/16″, from the object lines that extend outward perpendicular to features which are being dimensioned

DIMENSION LINES

Dimension lines are thin, solid, dark lines which indicate the direction and extent of a dimension. They are drawn to the same weight as a centerline, and should be thin enough to contrast with the object lines.

The dimension numbers are placed along the dimension lines. The dimension lines are placed between the extension lines, parallel to the features which are being dimensioned. Dimension lines have arrowheads at each end where they touch the extension lines. The one exception is in Architectural drafting where the arrowheads are replaced by diagonal hash marks where the dimension lines meet the extension lines. In most cases, the dimension line is at least 3/8″ from the object. When there are multiple dimension lines next to each other, they are placed at least 1/4″ apart outward from the object lines.

ARROWS

Arrows are placed at the ends of dimension lines to show the limits of the dimension. As with lettering and line quality, the quality of draftsmanship in arrowheads can make a significant difference in the overall look and readability of drawings. Arrowheads for leaders and dimension lines are drawn freehand and should be carefully made.

Arrowheads are drawn with two sharp strokes toward or away from the point. The length should be about 1/8″ and the width about one-third the length. For better appearance, they may be filled in. The solid arrowhead is generally preferred.

Avoid sloppy, careless arrowheads.

DIMENSION NUMBERS

Dimension numbers are the numbers that are placed with the dimension lines to indicate the size descriptions of the object features.

Size: Make dimension numbers 1/8″ tall unless otherwise specified by your supervisor.

Location: Depending upon the preference of the designer, the organization for which the designer is working, and individual industry practices, the numbers may either be placed right next to the dimension line, or the dimension line may be broken with the numbers placed within the path of the dimension lines.

The preferred method for dimensioning is to place the text within the dimension line when space permits.

Otherwise, place the text above the line.

If the space inside the extension lines is smaller than 3/8″, place the dimension lines and the numbers outside the extension lines.

Do not extend dimension lines across the open space between the extension lines.

Depending upon the dimensioning style being used, the numbers will either be aligned parallel with the dimension line, or unidirectional and aligned to the bottom of the page.

Dimensions of one foot and under are expressed in inches. Dimensions over one foot are expressed in feet and inches.

The width and thickness for steel plates are given in inches even if they are are wider than one foot. The length of the steel plate is given in feet and inches.

LEADER LINES

A Leader line is an angular line used to point out special characteristics of objects.  They are commonly used to specify sizes or circles and arcs. They are also used with notes.

Leader lines are thin, solid, dark lines, with an arrow at the end that touch and indicate the object feature being described. They will indicate the details of the feature with an associated local note. A leader does not require extension lines because it usually does not reference a linear distance. The arrowhead on the leader is always angular. The line is inclined at an angle ranging from 15° to 75° (30°, 45°, and 60° lines are common). A leader is never vertical or horizontal. When associated with a circle or an arc, the leader always points at or intersects the primary center of the round feature.

In most cases, a leader is drawn with a small horizontal tail called a shoulder. When the leader is to the left of the note, the shoulder connects to the beginning of the first line of information associated with the leader. When the leader is to the right of the note, the shoulder connects to the end of the last line of information associated with the leader. The shoulder typically extends 1/4″ from the leader line.

NOTES

The notes on a drawing may be either local or general in nature. The local notes are placed at the end of the leader lines to clearly define an object feature or move a description far enough away from the object to avoid cluttering the drawing. General notes are placed separately on the drawing according to standards and practices. The appropriate method depends upon the object’s features. Details of a local note depend upon the object’s features.

SIZE AND LOCATION DIMENSIONS

A location dimension locates holes or other object features. A size dimension states the sizes of any radius, diameter, length, width, angle, or thickness of an object.

Different styles of dimensioning may be applied to a drawing, depending on the designer and the company standards.

The most commonly used dimension styles are set forth in the ANSI standards.

 

 

 

 

 

 

 

 

 

 

 

TOLERANCE

Tolerance is the total acceptable variation within a dimension. The tolerance is the amount a particular dimension is allowed to vary during manufacturing. The design of parts for many complex applications requires a highly precise system of specifying dimensions and tolerances on drawings. Tolerances permit allowances in size from the specified dimension that may occur during manufacturing.

This is officially know as Geometric Dimensioning and Tolerancing (GD&T). Geometric dimensioning and tolerancing (GD&T) is a standard system devised to control interpretation of the form, profile, orientation, location, and runout of features on drawings. This type of tolerancing provides the necessary precision for the most economical manufacture of parts and interchangeable parts.

Establishing the number of decimal places represents the level of tolerance desired. Using three decimal places implies a higher level of tolerance than using two.

Plus and minus dimensioning is the allowable positive and negative variance from the dimension specified.

Limits of size is the largest acceptable size and the minimum acceptable size of a feature. The largest acceptable size is expressed as the maximum material condition (MMC) The smallest acceptable size is expressed as the least material condition (LMC).

GD&T uses geometric characteristic symbols to specify and explain form and positional tolerances. These symbols relate to such variables as the form of an object, the profile or outline of an object, the orientation of features, the location of features, and the runout of surfaces or relationship of features to an axis.

Here are some more terms related to tolerance dimensioning.

  • MMC :  Maximum Material Condition: Smallest hole or largest peg (more material left on the part)
  • LMC :   Least Material Condition: Largest hole or smallest peg (less material left on the part)
  • Virtual condition: Collective effect of all tolerances specified on a feature.
  • Datum target points: Specify on the drawing exactly where the datum contact points should be located. Three for primary datum, two for secondary datum and one or tertiary datum.

 

DIFFERENT TYPES OF COORDINATE DIMENSIONING

DATUM DIMENSIONING

The accuracy of the final product is determined by the dimension on the drawing. If all the dimensions originate from a common corner of the part, the object will be more accurate.

Rectangular coordinate dimensioning is where a base line (or datum line) is established for each coordinate direction, and all dimensions specified with respect to these baselines. This is also known as datum dimensioning, or baseline dimensioning. All dimensions are calculated as X and Y distances from an origin point, usually placed at the lower left corner of the part. Datums insure the tolerance or errors in the manufacturing do not accumulate.

Here is a set of visual representations about datum dimensioning.

POLAR COORDINATE DIMENSIONING

When parts of a drawing align on a common radial centerline, polar coordinate dimensions are used In this case, all radial dimension lines originate from a baseline with the largest dimension on the outside. All other dimensions progress inward to the smallest dimension.

 

DIMENSIONS ON A DRAWING

Below is a drawing with the components of dimensions for a drawing labeled

Each dimension should have two arrowheads associated with it, pointing in opposite directions. Dimensions can ‘share’ arrowheads.

The following depicts appropriate forms for linear dimensions.

7.1-7 Examples

Here is an example of a dimensioned drawing, with an isometric drawing included to increase clarity.

Top

7.2  Dimensioning Guidelines

 

7.2-1. Basic Guidelines

Special lines are used for dimensioning. (As a reminder of which line is which, you can refer to the Alphabet of Lines shown below.) These include dimension lines, extension lines, and leaders.

BASIC RULES:

  • Size dimensions are used to define length, width, height, diameter of circles and radii of arcs.
  • Position dimensions locate the center of circles and other key features.
  • Each dimension is clearly shown and stated so that it can be interpreted in only one way.
  • Dimensions are not to be duplicated or given on a drawing in two different ways. The size and p0osition of each feature is defined only once.
  • Dimensions are best placed in the view where the best shape and true form are shown.
  • The smallest dimensions should be closest to the object.
  • Avoid long extension and leader lines.
  • Put the dimension as close as possible to the feature it is describing, as long as the other basic rules are being followed.
  • Place dimensions between views, especially when they apply to both views and will improve clarity.
  • Spacing between dimensions should be consistent within a drawing.
  • Line up dimensions horizontally and vertically where possible.
  • Avoid crossing dimension lines or leaders where possible.
  • A correctly dimensioned drawing should be pleasing to the eye.

 

7.2-2 Types of Dimensions

Abbreviations and Symbols: You can conserve space and time by using abbreviations and standardized symbols. The following is a chart of dimensioning symbols to use on drawings:

A linear dimension is a dimension that is either horizontal or vertical to the dimensioning plane.

A leader dimension is a line used to point toward a diameter or radius.

A diameter dimension is a dimension that specifies a diameter of a circle. The diameter symbol is the symbol which is placed preceding a numerical value indicating that the associated dimension shows the diameter of a circle. The symbol used is the Greek letter phi. Ø

A radius dimension is used to specify a radius. The radius symbol is the symbol which is placed preceding a numerical value indicating that the associated dimension shows the radius of a circle. The radius symbol used is the capital letter R.

Hole dimensions are used to denote drilled hole information by using a leader line pointing toward the center of the hole.

An angular dimension is used to specify the amount of degrees between two lines that are parallel or co-linear to each other.

Here are some basic rules.

Size dimensions are used to define length, width, height, diameter of circles and radii of arcs.

  • Position dimensions locate the center of circles and other key features.
  • Each dimension is clearly shown and stated so that it can be interpreted in only one way.
  • Dimensions are not to be duplicated or given on a drawing in two different ways. The size and p0osition of each feature is defined only once.
  • Dimensions are best placed in the view where the best shape and true form are shown.
  • The smallest dimensions should be closest to the object.
  • Avoid long extension and leader lines.
  • Put the dimension as close as possible to the feature it is describing, as long as the other basic rules are being followed.
  • Place dimensions between views, especially when they apply to both views and will improve clarity.
  • Spacing between dimensions should be consistent within a drawing.
  • Line up dimensions horizontally and vertically where possible.
  • Avoid crossing dimension lines or leaders where possible.
  • A correctly dimensioned drawing should be pleasing to the eye.

http://rvhs-denyer.com/web-back/cad/units&tasks/led-ch-7-dimensioning/led-ch-7-dimensioning-text.htm

These are good, but even a fairly simple part can get messy very fast. If things get to messy go for a larger scale and drawing sheet if you can.  Don’t hesitate to pull out details and sections.  It’s always best to consider how the part is going to be measured and especially used. Here’s a case in point from above. The 1.8 on the angle is almost impossible to measure with any degree of accuracy. It’s better to dimension the ends of the angle and the angle itself. It’s also better to dimension from a natural if not an explicit datum like the dimensions on the bottom of  part.:

Dimension placement depends on the space available between extension lines. Normally. dimension notes are placed beside the dimension line. When space permits, dimensions and arrows are placed between the extension lines.

Here’s another slideshow with some basic dimensioning guidelines.

http://www.engineersedge.com/international_tol.htm

https://en.wikipedia.org/wiki/Geometric_dimensioning_and_tolerancing

Don’t do these.

http://www.etinews.com/techpaper_7deadly.html

Especially #3.

Never, ever change the title block tolerances unless you are the controlling authority.  Even then, think about it, think about it again and don’t do it.  The shop is used to what the title block tolerances are and more than likely won’t even read them.  So it’s MUCH better to specify the tolerances than to edit the title block tolerances. When you want +/- .001 and the shop gives you +/- .005 you are in trouble.  Title block tolerances should be loose anyway.

http://www.dtic.mil/ndia/2008technical/GastonEngineeringDrawings100G.pdf

Just remember that the goal is to avoid getting one of these back.

http://www.conradhoffman.com/RFQ_response.htm

Now if you are just getting  parts made for yourself any method of organization and storing files will work.  When you are working toward a real product, you are going to need to control your documents.  That small block on the lower right hand corner that says revision is probably the most critical thing that separates a hack from a product.  Controlling when and how changes are made in a design is crucial when a large number of different parties are involved.  Even simple parts can get screwed up royally and screw-ups get expensive very fast.  Setting up a document control system for technical and engineering information early in the design will save you a lot of grief.  The Cad software packages offer product data maintenance software with their packages and when you get to the point of more than one user, implementing a document control, even if it’s a locked folder with read only files can save you a pile of money.  Engineering documents should always have a fixed copy including any CAD files.  Along with a standard change procedure with a signoff process on the change. Having a ECN and Document process in place will keep you away from a ton of trouble and keep you from wasting time and big money.

While you could buy all the relevant standards for engineering documents, one of the best values is from the Genium Publishing company.  It’s the Drafting and standards manual started by General Electric.  It includes pages on how to draw just about everything, a copy of Ansi y14.5 and a CD with all the standards on it, along with a 6 month subscription.  Since Ansi y14.5 cost $300 by itself, having this book is just about covered by having that alone and there’s about a 1000 pages more of drafting and design material.  A definite must for a startup.

http://www.draftingzone.com/shoppingzone/#DM

This is just a beginning on this topic. There are entire classes and books on GD&T and even more references on drawing.  The important thing is to not get overwhelmed.  Starting out, you don’t need fancy drawing techniques and elaborate standard and practices.  Moving forward you will discover that the hard work is already done and all you have to do is adapt what already exist to your needs. Just remember to KISS(keep it simple and stupid) and you will do OK.

My general book list.

https://theartsmechanical.wordpress.com/2015/03/14/a-makers-and-engineering-bookshelf/

The Let’s Build Series.

https://theartsmechanical.wordpress.com/tag/lets-build/

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