How Precise is That Part? Know Your GD&T

How does a design go from the computer screen to something you hold in your hand? Not being able to fully answer this question is a huge risk in manufacturing because . One of the important tools engineers use to ensure success is Geometric Dimensioning and Tolerancing (GD&T).

A good technical drawing is essential for communicating your mechanical part designs to a manufacturer. Drafting, as a professional discipline, is all about creating technical drawings that are as unambiguous as possible, and that means defining features explicitly. The most basic implementation of that concept is dimensioning, where you state the distance or angle between features. A proper technical drawing will also include tolerances for those dimensions, and I recently explained how to avoid the pitfall of stacking those tolerances.

Dimensions and tolerances alone, however, don’t tell the complete story. On their own, they don’t specify how closely the geometric form of the manufactured part needs to adhere to your perfect, nominal representation. That’s what we’re going to dig into today with GD&T.

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Planned Obsolescence Isn’t A Thing, But It Is Your Fault

The common belief is that big companies are out to get the little people by making products that break after a short period, or with substantially new features or accessories that make previous models obsolete, requiring the user to purchase a new model. This conspiracy theory isn’t true; there’s a perfectly good explanation for this phenomenon, and it was caused by the consumers, not the manufacturers.

When we buy the hottest, shiniest, smallest, and cheapest new thing we join the wave of consumer demand that is the cause of what often gets labelled as “Planned Obsolescence”. In truth, we’re all to blame for the signals our buying habits send to manufacturers. Dig in and get your flamewar fingers fired up.

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Custom LCD Module is Unexpectedly Cheap and Easy

Looking to take your project to the next level in terms of functionality and appearance? A custom LCD display might be the thing that gets you there, at least compared to the dot-matrix or seven-segment displays that anyone and their uncle can buy from the usual sources for pennies. But how does one create such a thing, and what are the costs involved? As is so often the case these days, it’s simpler and cheaper than you think, and [Dave Jones] has a great primer on designing and specifying custom LCDs.

The video below is part of an ongoing series; a previous video covered the design process, turning the design into a spec, and choosing a manufacturer; another discussed the manufacturer’s design document approval and developing a test plan for the module. This one shows the testing plan in action on the insanely cheap modules – [Dave] was able to have a small run of five modules made up for only $138, which included $33 shipping. The display is for a custom power supply and has over 200 segments, including four numeric sections, a clock display, a bar graph, and custom icons for volts, amps, millijoules, and watt-hours. It’s a big piece of glass and the quality is remarkable for the price. It’s not perfect – [Dave] noted a group of segments on the same common lines that were a bit dimmer than the rest, but was able to work around it by tweaking the supply voltage a bit.

We’re amazed at how low the barrier to entry into custom electronics has become, and even if you don’t need a custom LCD, at these prices it’s tempting to order one just because you can. Of course, you can also build your own LCD display completely from scratch too.

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Using Pad Printers To Add Color To Artistic PCBs

I’ve done a few experiments in adding color to printed circuit boards. These experiments used a process known as pad printing, and so far all indications are that pad printing is a viable process for truly multicolor artistic PCBs. For this year’s DEF CON, I’m stepping things up and taking them to their logical conclusion. I’m making true multicolor PCBs with orange and blue ink. This is, I believe, the first time this has ever been done with printed circuit board art, and it is certainly the first time it has ever been documented.

You may be wondering why I need more color on my boards. It’s that time of year again where PCB artisans all around the world are gearing up for badgecon DEF CON. For the last few years, independent badge makers have come together to form a demoscene of hardware creation. This year, add-ons for badges are a thing, and everyone is getting in on the game. Tindie is filled with amazing electronic badges and add-ons that will be found at this year’s DEF CON. There are badges featuring the Cromulon from Rick and Morty, baby Benders from Futurama, pikachus, and glowing tacos.

This is all about badge art, but when it comes to rendering an image in fiberglass and soldermask, everyone is working with a limited palette. Yes, you can get pink and orange soldermask, but I can’t find a place that will do it inexpensively. For any PCB, your choice of colors are only green, red, yellow, blue, purple, black, or white. No, you can’t mix them.

But I want both orange and blue, on the same board, cheaply and easily — here’s how I did it.

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The Magic that Goes into Magnets

Every person who reads these pages is likely to have encountered a neodymium magnet. Most of us interact with them on a daily basis, so it is easy to assume that the process for their manufacture must be simple since they are everywhere. That is not the case, and there is value in knowing how the magnets are manufactured so that the next time you pick one up or put a reminder on the fridge you can appreciate the labor that goes into one.

[Michael Brand] writes the Super Magnet Man blog and he walks us through the high-level steps of neodymium magnet production. It would be a flat-out lie to say it was easy, but you’ll learn what goes into them and why you don’t want to lick a broken hard-drive magnet and why it will turn to powder in your mouth. Neodymium magnets are probably unlikely to be produced at this level in a garage lab, but we would love to be proved wrong.

We see these magnets everywhere, from homemade encoder disks, cartesian coordinate tables, to a super low-power motor.

Retrotechtacular: Constructing A Car Engine

Oxford is a city world-famous for its university, and is a must-see stop on the itinerary of many a tourist to the United Kingdom. It features mediaeval architecture, unspoilt meadows, two idylic rivers, and a car plant. That’s the part the guide books don’t tell you, if you drive a BMW Mini there is every chance that it was built in a shiny new factory on the outskirts of the historic tourist destination.

A 1930s Morris Ten Series II. Humber79 [CC BY-SA 3.0].
A 1930s Morris Ten Series II. Humber79 [CC BY-SA 3.0].
The origins of the Mini factory lie over the road on a site that now houses a science park but was once the location of the Morris Motors plant, at one time Britain’s largest carmaker. In the 1930s they featured in a British Pathé documentary film which we’ve placed below the break, part of a series on industry in which the production of an internal combustion engine was examined in great detail. The music and narration is charmingly of its time, but the film itself is not only a fascinating look inside a factory of over eight decades ago, but also an insight into engine manufacture that remains relevant today even if the engine itself bears little resemblance to the lump in your motor today.

Morris produced a range of run-of-the-mill saloon cars in this period, and their typical power unit was one of the four-cylinder engines from the film. It’s a sidevalve design with a three-bearing crank, and it lacks innovations such as bore liners. The metallurgy and lubrication in these engines was not to the same standard as an engine of today, so a prewar Morris owner would not have expected to see the same longevity you’d expect from your daily.

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Electronics Manufacturers React To China Trade Tariffs

Mere weeks ago, the United States announced it was set to impose a 25% tariff on over 800 categories of Chinese goods. These tariffs include nearly every component that goes into the manufacture of any piece of electronic hardware, from resistors to capacitors, semiconductors to microcontrollers, and even the raw components that are turned into printed circuit boards. These tariffs will increase the cost of materials for electronics, even if those electronics are ultimately manufactured in the United States because suppliers and subcontractors must source their materials from somewhere, and more often than not, that place is China.

Now, manufacturers are feeling the pinch. An email distributed by Moog Music last Friday has asked their supporters to contact their senators and representatives.

In the world of musical synthesizers, there is no bigger name than Moog. The company was founded in the 1950s manufacturing theremins, and in the 1960s, production moved to synthesizers. The famous Minimoog, launched in 1970, has been featured on tens of thousands of albums. Modern music simply wouldn’t exist without Moog synthesizers. After a buyout, mismanagement, and bankruptcy in the 1980s, the company was reborn in the early 2000s, moved into a beautiful factory in Asheville, North Carolina, and has gone on to produce some of the most popular synthesizers ever made.

The company’s statement says these new tariffs will, ‘immediately and drastically increase the cost of building our instruments, and have the very real potential of forcing us to lay off workers and could.. require us to move some, if not all, of our manufacturing overseas’. In a statement on Twitter, Moog says they source half their PCBs and a majority of other materials domestically, already paying up to 30% more than if the PCBs were sourced from China. However, because the raw materials for PCB manufacture are also sourced from China, board manufacturers for Moog’s synths will be forced to pass along the 25% tariff to their customers.

The threat of Moog being forced to move production of their instruments to China is real. Like cell phones, laptops, and other finished goods, synthesizers are not covered by the new tariff. As noted by Bunnie Huang, these tariffs have the perverse incentive of shifting US manufacturing jobs to China.

These tariffs have been a point of contention for the electronics and engineering communities. Anyone can easily pull up the distributor information from a Mouser or Digikey order and find the country of origin for an entire Bill of Materials. It has already been confirmed that most of the FR4 and other raw components that go into manufacturing PCBs in the United States come from Chinese suppliers. These items can be cross-referenced with the list of items that will be subject to a 25% tariff next week. Manufacturing electronics in the United States, even if you get your PCBs from US manufacturers and parts from US suppliers, will cost more in just a few short days.