Most of us are familiar with the concept of producing PCBs in a panel, and snapping them apart afterwards. V-grooves that go most of the way through a PCB are one way to go about this, but a line of perforations along which to snap a tab is another. But what’s the best size and spacing of holes to use? Sparkfun’s [Nick Poole] spent some $400 on PCBs to get some solid answers by snapping each of them apart, and judging the results.
The nice thing about creating a perforation line (or “mouse bites”) is that drill hits are a very normal thing in PCB production, which makes creating this kind of breakaway tab a very straightforward and flexible method. However, it can be tricky to get results that are just right. Too sturdy, and breaking apart is a hassle. Too weak, and the board may break or twist before its time. On top of that, edges must also break cleanly. We’ve covered panelizing PCBs in this way before, but this is the first time we’ve seen someone seriously look into how to create optimal breakaway tabs.
Data on designing mouse bites was sparse and a bit inconsistent, so [Nick] decided to figure it out empirically and share the results. The full details are available in Building a Better Mousebite (PDF download) but the essence of the recommendations are: 0.015″ unplated holes, spaced 0.025″ apart (center-to-center), tabs a maximum of 0.118″ wide (so as to be compatible with depanelizing tools), and holes that extend into the corners of the breakaway tab to avoid sharp edges. Holes should be placed slightly differently depending on whether one wishes to optimize the cosmetic appearance versus the physical smoothness of the board edge, but those numbers are the core of the guidelines.
To fine tune, [Nick] suggests increasing the spacing between holes to add strength, or just adding additional tabs. What about thickness of PCB? [Nick] tested boards both 0.8 mm and 1.6 mm thick, and while different amounts of torque were needed to snap the boards apart, things still worked as expected regardless of PCB thickness.
When it comes down to it, the best numbers will ultimately be the ones that your process or fab house can most efficiently handle, but [Nick]’s numbers should not steer anyone wrong, and it’s fantastic to see this kind of work go into refining such a common PCB feature.
After 30 Years, Genetic Study Confirms Sarin Nerve Gas As Cause of Gulf War Illness
Troops who had genes that help metabolize sarin nerve gas were less likely to develop symptoms. For three decades, scientists have debated the underlying cause…
The post After 30 Years, Genetic Study Confirms Sarin Nerve Gas As Cause of Gulf War Illness appeared first on SciTechDaily.
Original Source: scitechdaily.com
Vicious Little Desktop Shredder Pulverizes Plastic Waste
We’ve all likely seen video of the enormous industrial shredders that eat engine blocks for lunch and spit out a stream of fine metal chips. The raw power of these metal-munching monsters is truly fearsome, and they appear to be the inspiration for SHREDII, the miniature plastic shredder for at-home recycling of plastic waste.
The fact that SHREDII isn’t all that large doesn’t make it any less dangerous, at least to things smaller and softer than engine blocks, like say fingers. The core of the shredder is a hexagonal axle carrying multiple laser-cut, sheet steel blades. The rotating blades are spaced out along the axle so they nest between a bed of stationary blades; rotating the common axle produces the shearing and cutting action needed to shred plastic.
On version one of the shredder, each blade had two hooked teeth, and the whole cutting head was made from relatively thick steel. When driven by a NEMA 34 stepper — an admittedly odd choice but it’s what they could get quickly — through a 50:1 planetary gearbox, the shredder certainly did the business. The shreds were a little too chunky, though, so version two used thinner steel for the blades and gave the rotary blades more teeth. The difference was substantial — much finer shreds that were suitable for INJEKTO, their homebrew direct-feed injection molding machine.
There’s a lot to be said for closing the loop on plastics used in desktop manufacturing processes, and the team of SHREDII and INJEKTO stands to help the home gamer effectively reuse plastic waste. And while that’s all to the good, let’s face it — the oddly satisfying experience of watching a shredder like this chew through plastic like it isn’t even there is plenty of reason to build something like this.
Thanks for the tip, [Alen]!
Original Source: hackaday.com
Intense Exercise While Dieting May Reduce Cravings for High-Fat Food
In a new study that offers hope for human dieters, rats on a 30-day diet who exercised intensely resisted cues for favored, high-fat food pellets….
The post Intense Exercise While Dieting May Reduce Cravings for High-Fat Food appeared first on SciTechDaily.
Source Here: scitechdaily.com
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