Fighting Machine Tool Chatter with a 555 Timer

Vibration is a fact of life in almost every machining operation. Whether you’re milling, drilling, turning, or grinding, vibration can result in chatter that can ruin a part. Fighting chatter has generally been a matter of adding more mass to the machine, but if you’re clever about things, chatter reduction can be accomplished electronically, too. (YouTube, embedded below.)

When you know a little something about resonance, machine vibration and chatter start to make sense. [AvE] spends quite a bit of time explaining and demonstrating resonance in the video — fair warning about his usual salty shop language. His goal with the demo is to show that chatter comes from continued excitation of a flexible beam, which in this case is a piece of stock in the lathe chuck with no tailstock support. The idea is that by rapidly varying the speed of the lathe slightly, the system never spends very long at the resonant frequency. His method relies on a variable-frequency drive (VFD) with programmable IO pins. A simple 555 timer board drives a relay to toggle the IO pins on and off, cycling the VFD up and down by a couple of hertz. The resulting 100 RPM change in spindle speed as the timer cycles reduces the amount of time spent at the resonant frequency. The results don’t look too bad — not perfect, but a definite improvement.

It’s an interesting technique to keep in mind, and a big step up from the usual technique of more mass.

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Hacklet 44 – Teardowns

Just about every hacker, maker and tinkerer out there received their early education the same way: A screwdriver in one and a discarded bit of electronics in the other. There is no better way to find out how something works than cracking it open and examining each piece.  In recent years, teardown videos have become popular on YouTube, with some of the great examples coming from users like [EEVblog], [mikeselectricstuff], and [The Geek Group]. This week’s Hacklet is all about the best teardown projects on!

copierWe start with [zakqwy] and his Savin C2020 Teardown. Photocopiers (and multifunction machines) are the workhorses of the modern office. This means there are plenty of used, abused, and outdated photocopiers available to hackers. [Zakqwy] got this monster when it started misbehaving at his office. Copiers are a venerable cornucopia of motors, gears, sensors (lots and lots of breakbeam sensors) and optics. The downside is toner: it’s messy, really bad to breathe, and if you don’t wear gloves it gets down into the pores of your skin, which takes forever to get out. [Zakqwy] persevered and found some awesome parts in his copier – like an  Archimedes’ screw used to transport black toner.

wemoNext up is [Bob Blake] with Belkin WeMo Insight Teardown. [Bob] wanted a WiFi outlet, but wasn’t about to plug something in to both his power grid and his network without taking it apart first. [Bob] did an awesome job of documenting his teardown with lots of great high resolution photos – we love this stuff! He found a rather well thought out hardware design. The Insight has 3 interconnected PCBs inside. The power switching and supply circuits are all on one board. It includes slots and the proper creep distances one would expect in a design that will be carrying 120V AC mains power. A small daughter board holds an unknown chip – [Bob] is guessing it is the power sensing circuitry. A third board a tucked in at the top of the module holds the main CPU, a Ralink/MediaTek RT5350F SoC, RAM, and the all important WiFi antenna.


x-ray[Drhatch] took things into the danger zone with an X-ray Head Teardown. We’re not sure if [Drhatch] is a real doctor, but he does have a Heliodent MD dental X-ray head. Modern X-ray machines are generally radiation safe if they’re not powered up. Radiation isn’t the only dangers to worry about though – there are latent charged capacitors and cooling oils which may contain nasty chemicals like PCBs, among other things. [Drhatch] found some pretty interesting design decisions in his X-ray head. The tube actually fires through the cylindrical high voltage transformer. This means the transformer acts as a beam collimator, focusing the X-ray beam down like a lens. He also found plenty of lead shielding. Interestingly there are two thickness of lead in the housing. Shielding close to the tube is 1 mm thick, while shielding a bit further away is only 0.7 mm thick.


3phaseFinally, we have [danielmiester] with Inside a 3ph AC Motor Controller(VFD). [Daniel] tore down a Hitachi Variable-Frequency Drive (VFD) with the hopes of creating a frequency converter for a project. These high voltage, high power devices have quite a bit going on inside, so the conversion became a teardown project all its own. VFDs such as this one are used in industry to drive high power AC motors at varying speeds efficiently. As [Daniel] says, the cheaper ones are ” just really fancy PWM modules”. Handling 1.5 kW is no joke though. This VFD had a large brick of power transistors potted into its heat sink. The controller board was directly soldered to the transistors, as well as the rectifier diodes for the DC power supply. [Daniel] was doing some testing with the unit powered up, so he built a custom capacitor discharge unit from 3 C7 Christmas lights. Not only did they keep the capacitors discharged, they provided an indication that the unit was safe. No light means no charge.

Not satisfied? Want more teardown goodness? Check out our freshly minted Teardown List!

That’s about all the time we have for this week’s Hacklet. As always, see you next week. Same hack time, same hack channel, bringing you the best of!

Hacking a Christmas Tree for Less Blinkyness

Hacking a Christmas Tree to Blink Slower

What good is a fiber optic self-lighting Christmas tree if it flashes so fast it will put you into an epileptic attack? The answer is “Not very good”, if you ask [Mads Nielsen] a.k.a [EcProjects]. So [EcProjects ] started a little project to slow the Christmas tree’s blinkyness down to a more reasonable rate. The task didn’t seem too difficult at first but turned into a quality tutorial building a variable frequency H-bridge motor control.

After opening the base of the tree [EcProjects] found a 12 volt AC geared synchronous motor turning a multi colored translucent plastic disk. A bright spotlight was shining upwards through the turning disk into the ends of hundreds of small fiber optics. This mechanism dumps loads of multi colored light out the ends of the fibers at the tips of the Christmas tree branches as the disk turns.

His goal was to slow down the motor; however, the rotation was based on the 50 Hz mains signal. In order to continue using this motor a lower frequency AC power source was needed. What follows in the video is an excellent lesson on how an AC synchronous motor works plus how to build a variable frequency control and H-bridge using some transistors, resistors and CMOS 4069 inverter chip.

In the end the frequency drive could only be lowered to about 30 Hz before the synchronous motor would stall and reverse using his design. [EcProjects] was bold enough to include several fails which always provides more opportunity for learning and is greatly appreciated.

If you believe you have a better solution please share your idea in the comments. I’m sure the first proposal will include an Arduino and servo modified for continuous rotation, but any solutions would be fascinating including modifications to his design. You can join us after the break to watch the video.

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