Drawings 101

WHY DRAWINGS ARE IMPORTANT?

Communication:

Engineering drawings are a critical component of the product design and fabrication/ manufacturing/ construction process. They serve as the essential communication tool for a component or assembly's dimensions, materials, features, and a host of other characteristics. The quality and accuracy of engineering drawings directly impact the fit, form, and function of the final product. A well-crafted drawing ensures that the product meets its design specifications and functions as intended. In contrast, a poorly crafted drawing can result in defects and errors, costly rework, and potentially dangerous situations for those building a part and the end user.

Legal Context:

Effective communication through engineering drawings is essential to ensuring that everyone involved in the fabrication/ production/ construction process is on the same page and can succeed together. The drawing often serves as an essential defining element of legal contracts between parties. Many lawsuits have hinged around a vendor's/contractor's satisfaction of unclear engineering drawings. Attention to detail and proper use of this form language is therefore paramount when creating engineering drawings in order to avoid these types of issues all together.

Best Practices for Engineering Drawings

1. Drawings should be clear and uncluttered. Use a minimum number of views (Usually at least 2) that still allow for all features to be defined and dimensions.

2. Don’t dimension something more than once. Any double dimension that is used should be defined as reference placing it in parentheses.

3. Use symbols whenever possible instead of words.

4. Notes should be kept to a minimum. Any time excusive amounts of notes are required, a separate document should be used.

5. With a few exceptions, drawings should not detail the process to create the features. If required to outline how the part should be manufactured these details should go on a separate document often called a “Manufacturing Plan”.

6. With few exceptions Dimensions should be placed off the part and not on it.

7. Generally, when defining the location of features, dimensions should be coming from Datums unless there is a reason for the contrary like in the case where the distance between 2 holes is critical.

8. Where possible and practical Reference points (Datums) should be features that relate to the function of the part like a surface or edges that touches another part of an assembly or for example a hole that is key to the function of the part.

9. When determining the size of clearance holes for bolts and other fasteners use a chart or clearance hole calculator. These tools will allow you to pick the right amount of clearance for the application that will correspond to a standard drill size.

10. It is best practice to use all-caps for notes, etc., so turn on all-caps when you start to create a drawing.

11. Hidden lines should not be dimensioned.

12. All dimensions must have tolerance, either General, Specific, or GD&T.

13. Rev Levels should be kept up to date.

14. Use a standardized Template to save time and to give your drawings a uniform look.

COMMUNICATION BEYOND THE DRAWING

Drawings are tools for communicating, so if you have doubts about proper interpretation or clarity, go communicate with your audience. Stay engaged with your partners to make sure they have what they need to reach collective success. Remain paranoid about your work even after you let go of it. You have an ethical obligation to those who use your designs, so go check if your parts are coming out as you intended and never assume you did your job perfectly.

MTC DRAWING STANDARDS

Standards, like many spoken languages and dialects, can establish faster and clearer communication between parties, particularly in complex subject matters. For example, ASME Y14.5 lays down a framework for definition of complex parts with short-hand but exacting notation.

The Manufacturing Technology Center (MTC) prefers drawings that adhere to ASME Y14.5, but the MTC is able to work with other standards so long as information is clearly communicated.

A physical copy of ASME Y14.5-2018 can be found at the library. See Library Resources.

DRAWING EXAMPLES

Below are a set of annotated drawings for a variety of parts which teams should leverage to inform their drawings and learn new techniques they may not be familiar with.

MTC DRAWING NOTES

Drawing notes are a key piece of communication in the fabrication and assembly of components. Having clear notes which fully-specify what is necessary for a successful part without over-defining the means by which to achieve those results is extremely valuable.

In the case of the MTC, the following standard notes have been developed to define a set of processes the shop can commonly achieve or are at least a good starting point for drawing definition. Using standard notes can save a lot of time and improve confidence in your parts once you get used to using them.

These are not the only notes that the MTC or other fabricators can use, but they are suggested for ease of getting started or covering common tasks:

Materials

Example of a callout for a specific specification:

MATERIAL: SHEET STEEL PER AMS 5517 (COLD ROLLED 18-8 STAINLESS)

CONDITION: 1/4 HARD

Note that this type of callout (sheet steel used as example) will deliver a very exact type of material, but may be more difficult to source.

Example of a callout for a broad needs:

MATERIAL: [SERIES]-[TEMPER] ALUMINUM PER ANY SPEC

MIN TENSILE YEILD STRENGTH: [XX,XXX] PSI

MIN ELONGATION AT BREAK: [XX]%

Note that this type of callout will deliver a general category of material but may have varying properties depending on what spec and form is chosen. For example, directional properties are often different depending on the form of material such as sheet and strip vs billet vs plate vs round bar. Always be sure to understand what you need vs what you could get. If you are developing a prototype and you will be reviewing the specific material order for satisfying the analyzed requirements in all characteristics, you may not need to be as paranoid on the drawing; whereas if you are releasing a part for long-term production, many future material orders may not always satisfy your expectations unless you are very specific.

Example of a callout for 3D printed material:

MATERIAL: [POLYLACTIC ACID (PLA) ACRYLONITRILE BUTADIENE STYRENE (ABS), etc] PRINTED VIA FUSED DEPOSITION MODELING (FDM) PER MANUFACTUERER'S REQUIREMENTS

COLOR: [COLOR or ANY]

Holes & Threads

Typical Hole:

øX.XXX ± X.XXX

↧X.XXX ± X.XXX

øX.XXX ± X.XXX

THRU

Threaded Hole:

(øX.XXX) ↧X.XXX ± X.XXX*

1/4 - 20 UNC-2B PER ASME B1.1**

↧X.XXX MIN FULL THREAD DEPTH***

*The first line references the pre-drill diameter, but does not define it since the design actually only cares about the final thread fit which is defined in line 2. The first line does, however, establish how deep the pre-drill hole should be as this may effect other aspects of the part.

**Line 2 defines the thread type and engagement. 1/4-20 is used as a "Nominal Size & Threads/inch" example here which defines the standard thread major diameter and pitch. 2B is used as an example here of "Class" which determines a number of dimensional characteristics of the thread and the quality of its fit.

***Line 3 defines the depth of the thread. By using this note, it is implied that it is acceptable to have partial threads which extend beyond this measurement which may not accept threads.

Finish

Example of a bare finish note with optional processing to remove machining marks:

FINISH: BARE

[TUMBLE TO REMOVE ALL BURRS AND ESTABLISH ISOTROPIC FINISH] (if required)

[SAND BLAST TO ESTABLISH ISOTROPIC FINISH] (if required)

Example of a paint note for common paint configurations:

FINISH: PREP AND PAINT USING PRESSURE DRIVEN PAINT SYSTEM (SPRAY CAN OR GUN) PER PAINT MANUFACTURER'S INSTRUCTION

TYPE: [ENAMEL, ACRYLIC, WATER-BASED, OIL-BASED, etc]

COLOR: [CHOOSE COLOR]

FINISH: [GLOSS, MATTE, etc]

Cleaning

Example of basic cleaning note using common solvents:

CLEAN: REMOVE VISIBLE OILS, DIRT, AND DEBRIS FROM SURFACE WITH ISOPROPYL ALCOHOL (IPA) OR ALTERNATE [NON-CHLORONATED, etc.] [MILD CLEANER, DEGREASER, SOLVENT, ETC]

[VERIFY CLEAN WITH VISUAL INSPECTION UNDER WHITE LIGHT AND NO MAGNIFICATION. OILS, DIRT, AND DEBRIS MUST BE NON-VISIBLE.] (if required)

[VERIFY CLEAN WITH WIPE TEST. WHITE CLOTH MUST COME AWAY VISIBLY CLEAN FOLLOWING SINGLE WIPE ACROSS X INCHES OF SURFACE WITH FINGER PRESSURE] (if required)

Example of cleaning note for for a part which can be submerged:

CLEAN: RINCE WITH WATER AND MILD DETURGENT

[AIR DRY, BLOW DRY, TOWEL DRY] (if required)

Example of fast general clean:

CLEAN: BLOW OFF LOOSE DUST AND DEBRIS USING COMPRESSED AIR

Package & Identifying

General marking note which is easy to apply with accessable supplies:

IDENTIFY: PART MARK WITH PART NUMBER AND WORK ORDER (OR PURCHASE ORDER) IN LOCATION INDICATED

[USE PERMANANT INK PEN OR EQUIVALENT MARKING]

[USE LABEL OR TAG OR OTHER NON-PERMANANT METHOD OF MARKING]

General note for packaging and external identification:

PACKAGE & IDENTIFY: [BAG or BOX] PART AND TAG OR LABEL WITH PART NUMBER AND WORK ORDER (OR PURCHASE ORDER)

Minimum Dimension Drawing

An all-encompassing note for complex forms which utilizes GD&T per ASME Y14.5 to define the part based on the cad model and apply volumetric boundaries:

THIS IS A MINIMUM DIMENSION DRAWING PER ASME Y14.47. ALL DIMENSIONS NOT SHOWN ON DRAWING SHALL BE CONSIDERED BASIC PER THE CAD MODEL AND SHALL SATISFY |⌓|[.XXX]| AND |⌖|ø [.XXX] | A | B | C |

See the 3D printed part example for an application of this note.

Be cautious in use of this note. While it can do a lot of defining work, it can make it difficult to interpret and inspect a part. It is very useful for complex forms particularly in 3D printing which can be difficult to define in 2D space. You should never deploy this note, symbology, or GD&T without understanding how it works and the repercussions for your parts. An industry standard for this type of tolerancing, ASME Y14.5, can be found at the library.

Welding

This is a detailed weld note intended to define the weld procedure:

(MATERIAL: MILD STEEL)

PREP: GRIND MATERIAL TO EXPOSE BARE METAL, DO NOT REMOVE MORE THAT 0.010 PER SIDE, CLEAN W/ ACETONE UNTIL VISIBLY FREE OF DIRT & DEBRIS

WELD: [GMAW, GTAW, SMAW] PER [welding code such as D1.1]

MAX AMPERAGE: [XXX]A

MAX FILLER DIAM: [X/Y" such as 1/8"]

FILLER: [filler material spec such as ER705-6 PER AWS A5.18]

INSPECT:

VISUAL INSPECT [visual inspection requirements such as PER D1.1]

PENETRANT INSPECT [penetrant inspection requirements such as PER D1.1] (if required)

TYPE: [penetrant type such as VISIBLE DYE or FLORESCENT DYE] (if required)

SENSITIVITY: [penetrant test sensitivity level which is typically a number grading] (if required)

This type of note is typically referenced in the tail of a symbolic weld callout on the part.

System properties such as strength, corrosion resistance, and fatigue performance are often highly dependent on the weld process and procedure used. For this reason, it is not uncommon to have many limits and specifications invoked on drawings for welds. The reliability of welds is also often associated with the level of inspections (and resulting repairs if defects are found), therefore, design will typically define types and details of inspection required at the design level.

3D Printing

Mechanical Assembly

A note used to detail the installation of a lubricated fastener:

FASTENER INSTALL:

LUBRICATE FASTENER [LIGHTLY, WET, NON-VISIBLE LAYER, etc.] WITH [LUBRICANT]

TORQUE FASTENER TO [XX] [IN-LBS, FT-LBS, etc.] ± [X%]

[TORQUE STRIPE WITH PERMINANT PAINT PEN ONCE TORQUED]

A note used to detail the installation of a fastener with a thread locker:

FASTENER INSTALL:

LUBRICATE FASTENER [LIGHTLY, WET, NON-VISIBLE LAYER, etc.] WITH [LOCKTITE XXX, etc.]

TORQUE FASTENER TO [XX] [IN-LBS, FT-LBS, etc.] ± [X%]

[TORQUE STRIPE WITH PERMINANT PAINT PEN ONCE TORQUED]

NEVER BLINDLY DEFINE

Engineers should never use standards, symbology, notes, processes, or definitions in their work which they do not have a confident understanding of.

If you enticed to invoke a specification to define something on your drawing, go read the relevant portions of it until you understand it at a minimum.
If you are using a symbol and you're not sure what it really does, go review the source documentation (the real one, not some blog).
If someone says, "use this material," go look up it's properties from reputable sources and insure that it satisfies your requirements.

This may seem sinical and challenging, but engineering is a field of establishing processes to avoid failures and repeating mistakes.

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