The Tachometer Inside Your Smartphone

It’s the latest in instrumentation for the well-appointed shop — an acoustically coupled fast Fourier transform tachometer. Sounds expensive, but it’s really just using a smartphone spectrum analyzer app to indirectly measure tool speeds. And it looks like it could be incredibly handy.

Normally, non-contact tachometers are optically coupled, using photoreceptors to measure light flashing off of a shaft or a tool. But that requires a clear view of the machine, often putting hands far too close to the danger zone. [Matthias Wandel]’s method doesn’t require line of sight because it relies on a cheap spectrum analyzer app to listen to a machine’s sound. The software displays peaks at various frequencies, and with a little analysis and some simple math, the shaft speed of the machine can be determined. [Matthias] explains how to exclude harmonics, where to find power line hum, isolating commutator artifacts, and how to do all the calculations. You’ll need to know a little about your tooling to get the right RPM, and obviously you’ll be limited by the audio frequency response of your phone or tablet. But we think this is a great tip.

[Matthias] is no stranger to shop innovations and putting technology to work in simple but elegant ways. We wonder if spectrum analysis could be used to find harmonics and help with his vibration damping solution for a contractor table saw.

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Robotic Table Saw Automates Finger Joints

We’ve all seen finger joints or box joints, those interlocking puzzle pieces that make laser-cut plywood enclosures such a fixture for DIY projects. But laser cutters make finger joints look much easier to fabricate than they are with traditional woodworking tools, which often lead to disappointing results.

But this finger joint cutting robot is no traditional woodworking tool, and [timschefter] put a lot of work into building the rig. We have to admit that when we first saw the video below, the thought of having a table saw in our shop that could be turned on with a button on a phone gave us pause. But on closer analysis, it looks like safety was a major concern with this build. With a prominent e-stop and an interlock switch, the small table saw that forms the foundation of the robot should be safe enough. On the table top is a sled with a linear slide that moves the workpiece perpendicular to the blade, and the sled moves back and forth over the blade with pneumatic cylinders. The joint is set up with a custom app which calculates the pin width and spacing, which can be evenly distributed across the panel, or, for a bit of geeky fun, controlled to make a joint that encodes a message in Morse.

A lot of work went into this, and while it’s not the first robotic finger joint cutter we’ve seen, it’s pretty impressive. Now if it could only automate dovetails.

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Smooth and Steady Cuts with an Improvised Power Feeder

Some woodworking operations require stock to be fed at a smooth, steady rate, for which purpose a power feeder is usually employed. They’re expensive bits of gear, though, and their cost can usually be borne only by high-output production shops. But when you need one, you need one, and hacking a power feeder from a drill and a skate wheel is a viable option.

It should come as no surprise that this woodshop hack comes to us from [Matthias Wandel], who never seems to let a woodworking challenge pass him by. His first two versions of expedient power feeders were tasked with making a lot of baseboard moldings in his new house. Version three, presented in the video below, allows him to feed stock diagonally across his table saw, resulting in custom cove moldings. The completed power feeder may look simple — it’s just a brushless drill in a wooden jig driving a skate wheel — but the iterative design process [Matthias] walks us through is pretty fascinating. We also appreciate the hacks within hacks that always find their way into his videos. No lathe? No problem! Improvise with a drill and a bandsaw.

Surprised that [Matthias] didn’t use some of his famous wooden gears in this build? We’re not. A brushless motor is perfect for this application, with constant torque at low speeds. Want to learn more about BLDC motors? Get the basics with a giant demo brushless motor.

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A Fix for the Lightweight Machine Tool Shakes

No matter what material you work with, the general rule is that with machine tools, the heavier, the better. Some people can’t afford or don’t want big tools, though, even with their natural tendency to reduce vibrations. That doesn’t mean something can’t be done to help the little tools, like reducing vibration in a contractor-grade table saw.

This one might seem a little outside the usual confines of the hackosphere, but nobody can doubt [Matthias Wandel]’s hacker chops and he really shows off his problem-solving skills with this one. His well-worn contractor-style table saw has had more than a few special modifications over the years, some of which left it with a shimmy sufficient to vibrate workpieces right off the table. He fashioned a friction damper for the saw’s motor from wood, complete with ball and socket joints to allow full movement of the blade height and angle. That didn’t quite do the trick, but his incremental approach finally found the right combination of factors, and the video below shows a saw now stable enough to balance a nickel.

If the name seems familiar but you just can’t place the hacks, check out [Matthias]’s recent wooden domino extruder, his shortcuts to tapping wood, or of course his classic wood gears layout software.

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Adding a Riving Knife for Table Saw Safety

What in the world is a riving knife? Just the one thing that might save you from a very bad day in the shop. But if your table saw doesn’t come with one, fret not — with a little wherewithal you can add a riving knife to almost any table saw.

For those who have never experienced kickback on a table saw, we can assure you that at a minimum it will set your heart pounding. At the worst, it will suck your hand into the spinning blade and send your fingers flying, or perhaps embed a piece of wood in your chest or forehead. Riving knives mitigate such catastrophes by preventing the stock from touching the blade as it rotates up out of the table. Contractor table saws like [Craft Andu]’s little Makita are often stripped of such niceties, so he set about adding one. The essential features of a proper riving knife are being the same width as the blade, wrapping closely around it, raising and lowering with the blade, and not extending past the top of the blade. [Craft Andu] hit all those points with his DIY knife, and the result is extra safety with no inconvenience.

It only takes a few milliseconds to suffer a life-altering injury, so be safe out there. Even if you’re building your own table saw, you owe it to yourself.

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Internet Of Things Woodworking

Woodworking is the fine art of building jigs. Even though we have Internet-connected toasters, thermostats, cars, and coffee makers, the Internet of Things hasn’t really appeared in the woodshop quite yet. That’s changing, though, and [Ben Brandt]’s Internet of Things box joint jig shows off exactly what cheap computers with a connection to the Internet can do. He’s fully automated the process of making box joints, all with the help of a stepper motor and a Raspberry Pi.

[Ben]’s electronic box joint jig is heavily inspired by [Matthias Wandel]’s fantastic screw advance box joint jig. [Matthias]’ build, which has become one of the ‘must build’ jigs in the modern woodshop, uses wooden gears to advance the carriage and stock across the kerf of a saw blade. It works fantastically, but to use this manual version correctly, you need to do a bit of math before hand, and in the worst-case scenario, cut another gear on the bandsaw.

[Ben]’s electronic box joint jig doesn’t use gears to move a piece of stock along a threaded rod. Stepper motors are cheap, after all, and with a Raspberry Pi, a stepper motor driver, a couple of limit switches, and a few LEDs, [Ben] built an Internet-enabled box joint jig that’s able to create perfect joints.

The build uses a Raspberry Pi 3 and Windows IoT Core to serve up a web page where different box joint profiles are stored. By lining the workpiece up with the blade and pressing start, this electronic box joint jig automatically advances the carriage to the next required cut. All [Ben] needs to do is watch the red and green LEDs and push the sled back and forth.

You can check out [Ben]’s video below. Thanks [Michael] for the tip.

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That’s No Moon – That’s a Bamboo Death Star

At first glance, [Frank Howarth]’s turned bamboo Death Star seems like a straight woodworking project. No Arduino controlled lights, no Raspberry Pi for audio clips of an X-wing attack or escaping TIE fighter. In other words: where’s the hack?

It’s a freaking bamboo Death Star!

If that’s not enough for you, check out the pattern on the surface of the finished model. That’s not painted on – those are the layers of the laminated bamboo lumber used to create the rings [Frank] used to form the structure. After lots of turning, sanding and polishing, the characteristic vascular bundles of the bamboo create light and dark panels for a convincing effect of the Death Star’s surface detail. And although we like the natural finish, we can imagine a darker stain might have really made the details pop and made for an effect closer to the original.

Still not hackish enough? Then feast your eyes on [Frank]’s shop. It’s a cavernous space with high ceilings, tons of natural light, and seemingly every woodworking machine known to man. While the lathe and tablesaw do a lot of the work for this build, the drool-worthy CNC router sees important duty in the creation of the multiple jigs needed for the build, and for making the cutout for the superlaser, in what must have been a tense moment.

Bamboo is an incredible material, whether for fun builds like this or for more structural uses, like a bamboo bike. All this bamboo goodness puts us in the mood to call on [Gerrit Coetzee] for a new installment on his “Materials You Should Know” series.

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