Selecting Drawing Specifications

Manufacturing drawings are the language by which engineers communicate their design and requirements to production. These drawings can come in all manner of shapes, sizes, forms and formats. From napkin sketches with one dimension to model based design (MBD) packages, there is a format for everyone. As to be expected, these drawing packages have their own languages which take the form of drawing and dimensional standards. The standards are somewhat regional in nature, so as an engineer or designer it is critical to pick the correct standards based on where your parts will be manufactured.

Here at MFG Concepts, as part of our prototyping and manufacturing consultation services, we produce drawings in your specification of choice. We can even produce multiple packages for multiple manufacturers. Our goal is to ensure long term success of the design, meaning the drawing package should be prepared for the vendor, not just the engineer.

Background:

Production drawings have been a requirement so long as humans have been building. Ancient Greek and Roman buildings all required drawings. When the world started industrializing, it became clear that engineers needed a way to communicate better with their production personnel. Each engineer or designer had their own way of conveying ideas, which lead to confusion. Nationwide organizations began forming to standardize the format and thus language. Originally this was done to facilitate multiple companies all working together on railroads, arms manufacturing, or other large infrastructure projects. Later through organizations like DIN (Deutsche Institute of Standards), ANSI (American National Standards Institute), ASME (American Society of Mechanical Engineers) and finally ISO (International Organization for Standardization), ownership of standards was solidified.

ASME and ANSI Standards:

Most (over 85%) of US based companies utilize drawing formats that are ASME and ANSI standards. Even some foreign companies still utilize these standards. The US maintains its own drawing standards as a result of the Imperial Measurement System and its specific manufacturing heritage. Due to EAR and ITAR export-controlled information requirements, it can be critical to understanding these specifications when doing business in defense, aviation, automotive and other critical industries in the US.

The ANSI and ASME names for our sake are interchangeable as they both utilize the same standards. Some critical ones are:

ANSI Y14.1 – Paper sizes, while simple in nature, are the first trap for many designers. This standard tells us the size of the paper we can print on such as A (Letter) which is 8.5”x11” or B (Tabloid) which is 11”x17” on to C, D and E. When specifying a drawing this can lead to major issues if not adequately considered. For instance, if a drawing is generated for E which is 34”x44”, and the manufacturer cannot accommodate that size, they’ll have to break up the drawing onto A sheets. This can lead to missed or cut off dimensions, wreaking havoc on part manufacturing.

ASME Y14.5 – The US standard for geometric dimensioning and tolerancing (GD&T). This spec tells us how to define relations from one feature to another, and even how to write dimensions. At over 300 pages long, it is substantial.

ASME Y14.43 – The US standard for measuring a production part. This tells us how to use a dial indicator to check runout or what the tolerance of a gage pin should be for checking bore size.

ASME Y14.47 – This specification outlines how to utilize a model-based design (MBD) for manufacture. These MBDs are generated in CAD and never exported to a flat sheet. This requires the manufacturer to have CAD access and knowledge, but makes CNC programming much simpler. It also can be more intuitive, since the manufacturer can orbit the part and investigate any feature in whatever detail they require. Tolerances still need to be defined for manufacture, however.

DIN and ISO Standards:

These specifications are wide spread in usage across the rest of the world. Importantly, they utilize the metric system rather than the imperial system of measurement. DIN and ISO are quite similar for most specifications, even using the same numbering convention. As a rough rule of thumb, DIN is more common in Northern Europe where ISO is more prevalent in Asia. In addition, ISO specs are much shorter, and typically more specific. Instead of one 300-page drawing standard, there’s several 10-page documents. Some of the critical standards are:

ISO 128 – This covers the general rules for drawing production. From which views to include to where they should be located. The title block has its own spec in ISO 7200. See what I mean by many specs.

ISO 1101, 2768 and 5459 – These cover geometric dimensioning and tolerancing (GD&T) and how to inspect for each. Unlike the ASME spec, each of these specs covers the dimension and how to measure it. 5459 specifies how to locate datums and reference to them. 2768 is a multi-part standard which identifies functional tolerancing such as perpendicularity or symmetry in part 2, as well as simple linear or angular dimensions in part 1. 1101 is a more generic specification outlining symbols and principles.

ISO 16792 – The ISO specification for model-based designs (MBD). This specification functions similarly to its ASME counterpart with the same benefits and drawbacks.

What it means for you:

With modern CAD packages drawing standard selection has become easier in some ways, but certain knowledge is lost. By using drawing wizards common to most packages, tolerances are selected for features without any specific tolerancing specification knowledge required. The tolerances are then pasted onto the drawing based on the specification chosen (ISO/DIN/ANSI/ASME).

Companies typically have a template employees rely on which utilizes one off these languages. As a result, they typically will only produce drawings of one type, regardless of the end manufacturer. This is not an issue when the manufacturer and designer speak the same language. Unfortunately, in a global economy, that is rarely the case. Think a US company designing a part to be manufactured in China. All their drawings are per ASME Y14.5, but the vendor only knows ISO. As a result, the vendor has to translate the drawing, leading to increased cost and sources of error.

This is why at MFG Concepts we put a focus on the end user of the drawing package. Our belief is that to best serve the customer, a prototype package should be affordable to manufacture securely. Depending on the product, we might provide three drawing packages to fit every step in the product development journey. A tailored package is often overlooked, but can make all the difference in the market place.

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