Swedish Rocket Knives

There are trends in YouTube videos among various video producers. A few weeks ago, it was all about fidget spinners until some niche tech blog ran that meme into the ground. Before that, the theme was red-hot knives cutting through stuff. The setup was simple; just heat a knife up with a blowtorch, cut through a tomato or golf ball, hit stop on the high-speed camera, and collect that sweet, sweet YouTube money.

[David] from RCExplorer.se isn’t like most YouTube stars. He actually knows what he’s doing. When the latest trend of rocket-propelled knives hit the tubes, he knew he could blow this out of the water. He succeeded with a fantastic rocket-propelled machete able to slice through watermelons and fling itself into the woods behind [David]’s house.

Unlike most of the other YouTube stars trying their hand at rocket-powered slicers, [David] is doing this one right. He’s using hobby rocket motors, yes, but they’re reloadable. [David] crafted an engine casing complete with a proper nozzle machined out of stainless for this build. The rocket sled itself is an aluminum bracket bolted to a piece of carbon fiber plate that travels down a rail with the help of four skateboard wheels. A machete is then bolted to the plate, which is propelled down the track a bit faster than 200 km/h.

When it comes to rocket-propelled knives, the word ‘professional’ really doesn’t come into play. This, however, is an amazing piece of craftsmanship that you can check out in the videos below.

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Turning and Burning with a CNC Pyrography Machine

With CNC machines, generally the more axes the better. Three-axis machines with a vertical quill over a rectangular workspace are de rigueur, and adding an axis or two can really step up the flexibility of a machine. But can only two axes be of any use? Sure can, as witnessed by this two-axis CNC wood burning machine.

As [tuckershannon] tells the tale, this was a newbie build aided by the local hackerspace. Axis one is a rotary table of laser-cut wood gears powered by a stepper. Axis two is just a stepper and lead screw sitting on a couple of blocks of wood. A Raspberry Pi under the hood controls the motors and cycles the pyrography pen on and off as it scans across a piece of wood on the rotary table, burning a spiral pattern that makes for some interesting art. Hats off to [tuckershannon] for figuring out the math needed to adapt to the changing speed of the pen over the wood as the diameter gets bigger.

We love this build, can’t help but wonder if some clever gearing could eliminate the need for the second stepper. And perhaps an upgrade from the standard resistive wood burner to an arc lighter pyrography pen would improve resolution. Still, it’s hard to argue with results, and this is a great hack.

[via r/raspberrypi]

Thanks to [Liz] for the tip!

CNC Mill out of a Building Set

I have some aluminum building-set parts on hand and just got a second rotary tool, so I thought I’d try my hand at making a light-duty CNC mill—maybe carve up some cheap pine or make circuit boards. This post explores some of the early decisions I’m facing as I begin the project.

Of primary importance is the basic format of the mill’s chassis. Gantry configuration or put everything in a box of girders? How will the axes move–belts or racks? How will the Z-axis work, the assembly that lowers the tool onto the material? Finally, once the chassis is complete, or perhaps beforehand, I’ll need to figure out how I intend to control the thing.

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Fabricate Your Own Tabletop Gaming Props

Delve into the mysterious world of tabletop roleplaying games. Warhammer Fantasy Roleplay, Shadowrun, Pathfinder, Ars Magica, Vampire, whatever gets your dice rollin’ — metaphorically in the case of a diceless system. This might very well be your daddy’s D&D. If you’re not a gamer, you’re certainly familiar with the concept. People sit around a table pretending to have an epic adventure, often adding a random element with the help of dice. A map is often displayed on the table, sized for figures that show the various heroes and villains.

As a person with access to a variety of CNC machines I find myself wanting to create things to make gameplay more fun. I want to build a scale castle and have a siege. I want to conduct a ship-to-ship battle with wooden ships built to scale. But I also think smaller. What is something I could make that would help us every day? Say, a box for dice. Not every project needs to be the dragon’s lair.

It turns out a lot of other folks have been thinking about the same thing.

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Laser Cutting Orreries

An orrery is a clockwork model of the solar system, demonstrating the machinations of the planets traveling around the sun in a sublime pattern of epicycles. A tellurion is a subset of the orrery, showing the rotation of the Earth around the sun, and the orbit of the moon around the Earth. [HuidongT] created his own tellurion out of laser-cut parts and just a few bits of copper tubes and bearings.

This project was originally inspired by the holzmechanik, a tellurion constructed from plywood gears and brass tube. [HuidongT] saw a few shortcomings in this project: the Earth didn’t spin and the moon didn’t orbit with its natural five-degree inclination. [Huidong]’s tellurion would have these features and include an illuminated sun, demonstrate the change of the seasons, and show lunar and solar eclipses.

While there was a bit of math involved in figuring out the gearing, it’s not much: the Earth would go around the sun every 365.25 days, the moon would go around the Earth every 27.32 days, and there is a difference between sidereal and solar time. A quick script made quick work of the math, and anyone can easily find tools to create gears given a diameter and the number of teeth.

The fabrication of this tellurion was made with acrylic on a laser cutter with a handful of 3D printed parts. The electronics are simple enough — just a motor and a few LEDs, and the completed project works well enough. You can check out a video of the tellurium below.

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A Poor-Man’s Laser CNC Engraver

What do you get when you mix the disappointment that sometimes accompanies cheap Chinese electronics with the childhood fascination of torturing insects with a magnifying glass on a sunny day? You get a solar-powered CNC etcher, that’s what.

We all remember the days of focussing the sun on a hapless insect, or perhaps less sadistically on a green plastic army man or just a hunk of dry wood. The wonder that accompanied that intense white spot instantly charring the wood and releasing wisps of smoke stayed with you forever, as seemingly did the green spots in your vision. [drum303] remembered those days and used them to assuage his buyer’s remorse when the laser module on his brand new CNC engraver crapped out after the first 10 minutes. A cheap magnifying glass mounted to the laser holder and a sunny day, and he don’t need no stinkin’ lasers! The speed needs to be set to a super slow — 100mm per minute — and there’s the problem of tracking the sun, but the results are far finer than any of our childhood solar-artistic attempts ever were.

Do we have the makings of a possible performance art piece here? A large outdoor gantry with a big Fresnel lens that could etch a design onto a large piece of plywood would be a pretty boss beachside attraction. Of course, you’d need a simple solar tracker to keep things in focus.

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Download and Laser Your Own Pulleys

[Scott Swaaley] needed a bunch of timing pulleys for the clock he was building. He had already decided on the MXL profile, but he needed so many of these toothed pulleys in so many configurations (hex-bored, hubless) that it would blow out his budget. Plus, he wanted them transparent as well. So why not just laser them out of acrylic?

Not finding anything useful on the manufacturers’ sites, [Scott] decided to create his own web application to generate the shapes and download them as SVGs, dreaming of a resource like Gear Generator except for timing pulleys instead of involute spur gears. [Scott] has the application running on his GitHub. You can create MXL, XL, and L pulleys with any number of teeth and any hole size. From there you can output as an SVG and laser or mill the pulley.

There’s a lot of potential for projects made with pulleys and we’ve covered them extensively. Check out a 3D-printed strain wave gear, an inexpensive XY table, and even a remote operated gate for more pulley ideas.