Why Do We Have To Follow Drawing Standards?

December 14, 2020 John Burkhert

Can you imagine? There was a time when creating drawings meant using paper and a pencil. The main variable was the type of so-called lead in the pencil. Even in those primitive times, it was necessary to agree on an overall language. The particulars that allow the community to get their message across were determined by standards. The standards, in turn, were driven by the requirements of the equipment that archived and reproduced the drawings.

hand drawing schematic

Image Credit: AutoGuide - Pencil work was a job in itself.

Archives: One Driver of Drawing Standards

One of those pieces of equipment was microfilm. You might recall that microfilm was used to store lots of drawings in a small space. Bringing those tiny pictures back to human-readable sizes would lose some of the sharpness of the data. The standards were set up so that we could still make out the images and data with no doubt about what we saw.

Drafters would pencil in the linework and run the pencil over the object lines again and again to make sure it was certain to come back from the photographic shrinkage. Text sizes and, importantly, space between characters, was a function of the size of the drawing. Smaller A and B size documents could use .125 inch minimum text height while C-size formats and above required .140” letters and numbers. Minimum spacing between rows is half of the text height so that taller lettering gets more space. 

Text size is one example of typical drawing requirements. When it came to Department of Defence work, there were, and are, a huge ecosystem of standards. One document will reference several others. Those documents, in turn, will expand to other relevant documents. It seems as if the entire Library of Congress is in play by the time all of the interlinked specifications are on the table.

The government will set the bar for their vendors and will send auditors out with calipers to measure the size of the text and other aspects of the documentation. Their rules are enforced by the authority to stop shipments if the overall document package fails to meet expectations. In a way, they’re not even concerned with the product itself. Their primary concern is that the entire program can be resurrected from the microfilm records if the company itself was somehow removed from the face of the earth.

A Custom Carries Forward out of Momentum 

Bureaucracy in the commercial sector is trying hard to catch up and move forward at the same time. ISO, ANSI, IPC and other organizations are looking to replicate the process control without quite so much emphasis on reliability, traceability and excruciating completeness. Businesses that do not work on government contracts are free to adopt whatever methodology they choose including making up their own.

There is no legal mechanism to hold the consumer product documents to any standards. Telecoms and other large outfits that work both sides of the fence are likely to keep their sub-contractors in line with prevailing practices. Supplier guidance is a valid strategy when you’re flying by the seat of your pants. You will have to grow into a system eventually. It’s how we keep the wheels turning.

For the most part, the IPC and other standards organizations took the governmental regulations as a template. From there, they could strip away the unnecessary mumbo-jumbo and add in the particulars for enterprise. For example we still categorize PCBs for toys as class-1 while business machines are class-2 and high reliability is class 3. The entire build scheme of a hardware product is based on those three buckets.

General Principles of Documentation

  • Everything should be traceable to a standard definition.

  • Document everything once then refer to the controlling document for the characteristic.

  • A drawing is a what-is document.

  • A procedure is a how-to document.

  • Continuous improvement - don’t allow success to slow the march of progress.

  • Maintain a tight logistics loop including revision control and traceability of inventory.

  • These and other measures apply to the entire supply chain.

What we mean by traceability in a document sense is that somewhere, there is a source of the information and that source is in a secure location. We can retrieve that data any time we need it. As far as physical inventory, the dynamic includes not only the part number and revision but the time, place and purpose that the item was procured in the first place.

Documenting everything once dovetails with traceability in that a second source of information that contradicts the first needs to be avoided. The top document in that case is the laws of the locality followed by the contract, the purchase order, then the particular drawings and finally the standards called out to fill in the gaps. In a smaller sense, it applies to the application of dimensions so that there is only one way to interpret the physical minimum and maximums.

drawing requirements manual

Image Credit: Ebay - A phone book size style guide where the word “shall” means something very specific. New 11th edition copies are priced near $900 USD.

Fabrication and Assembly Drawings are considered to be inspection documents that depict a completed unit. While there are exploded view images that can be generated, they’re best used as an illustration in a process document. The main difference is that a procedure is limited to letter size paper while drawings make up the larger paper sizes.

That may seem like nonsense in a world where a .pdf file can be any size we like. Still, there’s more to it than keeping the drafters out of the loop of the factory flow documentation. A binder with the relevant specs is more practical than a drawing that covers the whole desk. Rework instructions and test procedures also fit the small format mold. Some of this is clearly a hangover from a time when computer monitors were not sitting on every desk in the factory.

A key principle is that of continuous improvement. That’s why we have the revision block. We’re expected to stress test the product to the breaking point. Then, whatever broke is strengthened and the product torture starts over. Extending beyond the Reliability Lab, we strive to improve all aspects of engineering execution in pursuit of a prosperous product lifecycle.

Getting everyone in your organization on board is a horizontal approach. A big part of continuous improvement is extending it through the entire vertical. The prime contractor is responsible to the customer but also has to be a conduit to the subcontractors to make sure that they are in compliance and passing it down to their vendors. Doing all of this with a complete paper trail is costly.

drawing requirements manual

Image Credit: Amazon - Jerome Lieblich has made a life’s work of documenting the documentation process.

Much of the commercial sector is not obliged to take it to that extent. The automotive industry comes to mind as a place where definitive quality control is a must. If a defective component was used and found to be an issue down the road, all instances of that component have to be replaced through a recall.

Managing their inventory so that they have provenance of every part helps ensure that they don’t have to replace every example if the failure is contained to a certain lot or date code. Pushing the requirement down through the supply chain strengthens the awareness of quality while enabling the factory to pinpoint problem parts.

Creating documents that convey the design requirements is the essential deliverable of our job. We can call it artwork but it is also very technical work that helps determine outcomes. While the reason for some of the documentation procedures seem to be from another time, they serve the continuity that allows us to communicate our own goals. As an organization grows, so does the formality of their documents. All we have to do is improve it a little every day.

 

About the Author

John Burkhert

John Burkhert Jr is a career PCB Designer experienced in Military, Telecom, Consumer Hardware and lately, the Automotive industry. Originally, an RF specialist -- compelled to flip the bit now and then to fill the need for high-speed digital design. John enjoys playing bass and racing bikes when he's not writing about or performing PCB layout. You can find John on LinkedIn.

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