Harmonic Analyzer Does It With Cranks And Gears

Before graphic calculators and microcomputers, plotting functions were generally achieved by hand. However, there were mechanical graphing tools, too. With the help of a laser cutter, it’s even possible to make your own!

The build in question is nicknamed the Harmonic Analyzer. It can be used to draw functions created by adding sine waves, a la the Fourier series. While a true Fourier series is the sum of an infinite number of sine waves, this mechanical contraption settles on just 5.

This is achieved through the use of a crank driving a series of gears. The x-axis gearing pans the notepad from left to right. The function gearing has a series of gears for each of the 5 sinewaves, which work with levers to set the magnitude of the coefficients for each component of the function. These levers are then hooked up to a spring system, which adds the outputs of each sine wave together. This spring adder then controls the y-axis motion of the pen, which draws the function on paper.

It’s a great example of the capabilities of mechanical computing, even if it’s unlikely to ever run Quake. Other DIY mechanical computers we’ve seen include the Digi-Comp I and a wildly complex Differential Analyzer. Video after the break.

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Making Models With Lasers

Good design starts with a good idea, and being able to flesh that idea out with a model. In the electronics world, we would build a model on a breadboard before soldering everything together. In much the same way that the industrial designer [Eric Strebel] makes models of his creations before creating the final version. In his latest video, he demonstrates the use of a CO2 laser for model making.

While this video could be considered a primer for using a laser cutter, watching some of the fine detail work that [Eric] employs is interesting in the way that watching any master craftsman is. He builds several cubes out of various materials, demonstrating the operation of the laser cutter and showing how best to assemble the “models”. [Eric] starts with acrylic before moving to wood, cardboard, and finally his preferred material: foam core. The final model has beveled edges and an interior cylinder, demonstrating many “tricks of the trade” of model building.

Of course, you may wish to build models of more complex objects than cubes. If you have never had the opportunity to use a laser cutter, you will quickly realize how much simpler the design process is with high-quality tools like this one. It doesn’t hurt to have [Eric]’s experience and mastery of industrial design to help out, either.

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Cardboard Longboard Uses Quarter-Isogrid Structure

Skateboards are most typically crafted by hand, carved out of wood layered by care. However, many makers have sought to explore alternative techniques. [Technovation] decided to combine alternative materials and digital fabrication techniques to produce this attractive cardboard longboard.

The structure of the board was designed in Fusion 360, featuring a quarter isogrid design. The structure consists of stringers connected by ribs, all made of cardboard, with interlocking slots to hold everything together. 1/4″ plywood is then used to reinforce the truck mounts, and a top and bottom baseplate of 4mm acrylic is installed to protect the cardboard from damage.

The parts for the board are all laser cut, making production and assembly a snap. No glue is used, either – the structure is able to hold itself together perfectly well with its slotted construction. The team note that having a rider on the board does create some significant flex, but it hasn’t caused a failure in practice.

Skateboards are a popular maker project, and we’ve seen all kinds over the years. Modern manufacturing techniques are often brought to bear, or designs are created to solve tricky travel problems. Video after the break.

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Laser Cutting Wooden Pogo Pin Test Jigs

Now as far as problems go, selling so many products on Tindie that you need to come up with a faster way to test them is a pretty good one to have. But it’s still a problem that needs solving. For [Eric Gunnerson] the solution involved finding a quick and easy way to produce wooden pogo test jigs on his laser cutter, and we have a feeling he’s not the only one who’ll benefit from it.

The first step was exporting the PCB design from KiCad into an SVG, which [Eric] then brought into Inkscape for editing. He deleted all of the traces that he wasn’t interested in, leaving behind just the ones he wanted to ultimately tap into with the pogo pins. He then used the Circle tool to put a 0.85 mm red dot in the center of each pad.

You’re probably wondering where those specific parameters came from. The color is easy enough to explain: his GlowForge laser cutter allows him to select by color, so [Eric] can easily tell the machine to cut out anything that’s red. As for the size, he did a test run on a scrap of wood and found that 0.85 mm was the perfect dimensions to hold onto a pogo pin with friction.

[Eric] ran off three identical pieces of birch plywood, plus one spacer. The pogo pins are inserted into the first piece, the wires get soldered around the back, and finally secured with the spacer. The whole thing is then capped off with the two remaining pieces, and wrapped up in tape to keep it together.

Whether you 3D print one of your own design or even modify a popular development board to do your bidding, the test jig is invaluable when you make the leap to small scale production.

The Practical Approach To Keeping Your Laser In Focus

You could be forgiven for thinking that laser cutters and engravers are purely two dimensional affairs. After all, when compared to something like your average desktop 3D printer, most don’t have much in the way of a Z axis: the head moves around at a fixed height over the workpiece. It’s not as if they need a leadscrew to push the photons down to the surface.

But it’s actually a bit more complicated than that. As [Martin Raynsford] explains in a recent post on his blog, getting peak performance out of your laser cutter requires the same sort of careful adjustment of the Z axis that you’d expect with a 3D printer. Unfortunately, the development of automated methods for adjusting this critical variable on lasers hasn’t benefited from the same kind of attention that’s been given to the problem on their three dimensional counterparts.

Ultimately, it’s a matter of focus. The laser is at its most powerful when its energy is concentrated into the smallest dot possible. That means there’s a “sweet spot” in front of the lens where cutting and engraving will be the most efficient; anything closer or farther away than that won’t be as effective. As an example, [Martin] says that distance is exactly 50.3 mm on his machine.

The problem comes when you start cutting materials of different thicknesses. Just a few extra millimeters between the laser and your target material can have a big difference on how well it cuts or engraves. So the trick is maintaining that perfect distance every time you fire up the laser. But how?

One way to automate this process is a touch probe, which works much the same as it does on a 3D printer. The probe is used to find where the top of the material is, and the ideal distance can be calculated from that point. But in his experience, [Martin] has found these systems leave something to be desired. Not only do they add unnecessary weight to the head of the laser, but the smoke residue that collects on the touch probe seems to invariably mar whatever surface you’re working on with its greasy taps.

In his experience, [Martin] says the best solution is actually the simplest. Just cut yourself a little height tool that’s precisely as long as your laser’s focal length. Before each job, stick the tool in between the laser head and the target to make sure you’re at the optimal height.

On entry level lasers, adjusting the Z height is likely to involve turning some screws by hand. But you can always add a motorized Z table to speed things up a bit. Of course, you’ll still need to make sure your X and Y alignment is correct. Luckily, [Martin] has some tips for that as well.

Creating A Laser Cutter From A 3D Printer

The average FDM 3D printer is not so different from your garden variety laser cutter. They’re often both Cartesian-coordinate based machines, but with different numbers of axes and mounting different tools. As [Gosse Adema] shows, turning a 3D printer into a laser cutter can actually be a remarkably easy job.

The build starts with an Anet A8 3D printer. It’s an affordable model at the lower end of the FDM printer market, making it accessible to a broad range of makers. With the help of some 3D printed brackets, it’s possible to replace the extruder assembly with a laser instead, allowing the device to cut and engrave various materials.

[Gosse] went with a 5500 mW diode laser, which allows for the cutting and engraving of wood, some plastics and even fabrics. Unlike a dedicated laser cutter there are no safety interlocks and no enclosure, so it’s important to wear goggles when the device is operating. Some tinkering with G-Code is required to get things up and running, but it’s a small price to pay to get a laser cutter on your workbench.

We’ve seen [Gosse]’s 3D printer experiments before, with the Anet A8 serving well as a PCB milling machine.

A Laser Cutting 101

If you’ve worked with a laser cutter before, you might not find much new in [Maker Design Lab’s] recent post about getting started. But if you haven’t, you’ll find a lot of practical advice and clean clear figures. The write up focuses on a tube-style laser cutter that uses a gas-filled tube and mirrors. Some cheap cutters use a diode, and many of the same tips will apply to those cutters.

You can probably guess that a laser cutter can cut like a CNC and also engrave where the cut doesn’t go all the way through. But it can also mark metals and other surfaces by using a marking solution. If you’ve done CNC or 3D printing, the process is similar, but there are a few unique things to know, like the use of the marking solution.

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