Pack Your Plywood Cuts with Genetic Algortihms

Reading (or writing!) Hackaday, we find that people are often solving problems for us that we didn’t even know that we had. Take [Jack Qiao]’s SVGnest for instance. If you’ve ever used a laser cutter, for instance, you’ve probably thought for a second or two about how to best pack the objects into a sheet, given it your best shot, and then moved on. But if you had a lot of parts, and their shapes were irregular, and you wanted to minimize materials cost, you’d think up something better.

SVGnest, which runs in a browser, takes a bunch of SVG shapes and a bounding box as an input, and then tries to pack them all as well as possible. Actually optimizing the placement is a computationally expensive proposition, and that’s considering the placement order to be fixed and allowing only 90 degree rotations of each piece.

Once you consider all the possible orders in which you place the pieces, it becomes ridiculously computationally expensive, so SVGnest cheats and uses a genetic algorithm, which essentially swaps a few pieces and tests for an improvement many, many times over. Doing this randomly would be silly, so the routine packs the biggest pieces first, and then back-fills the small ones wherever they fit, possibly moving the big ones around to accommodate.

That’s a lot of computational work, but the end result is amazing. SVGnest packs shapes better than we could ever hope to, and as well as some commercial nesting software. Kudos. And now that the software is written, as soon as you stumble upon this problem yourself, you have a means to get to the solution. Thanks [Jack]!

Laser Cut-and-Weld Makes 3D Objects

Everybody likes 3D printing, right? But it’s slow compared to 2D laser cutting. If only there were a way to combine multiple 2D slices into a 3D model. OK, we know that you’re already doing it by hand with glue and/or joints. But where’s the fun in that?

LaserStacker automates the whole procedure for you. They’ve tweaked their laser cutter settings to allow not just cutting but also welding of acrylic. This lets them build up 3D objects out of acrylic slices with no human intervention by first making a cutting pass at one depth and then selectively re-welding together at another. And they’ve also built up some software, along with a library of functional elements, that makes designing these sort of parts easier.

There’s hardly any detail on their website about how it works, so you’ll have to watch the video below the break and make some educated guesses. It looks like they raise the cutter head upwards to make the welding passes, probably spreading the beam out a bit. Do they also run it at lower power, or slower? We demand details!

Anyway, check out the demo video at 3:30 where they run through the slice-to-depth and heal modes through their paces. It’s pretty impressive.

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Laser-cut Cardboard Planetary Gearset is Pretty, but Useless

[Shane] made a project that speaks directly to our heart — combining laser cutting, cardboard, and gears. How could it be any better? Well, it could do anything. But that’s quibbling. It’s fun enough just to watch the laser-cut cardboard planetary gears turn. (Video after the break.)

It was made on a laser cutter using the gear extensions for generating gears in Inkscape, everybody’s favorite free SVG editor.

In his writeup, [Shane] touches on all of the relevant details: all of the gear pitches need to be the same, and the number of teeth in the sun gear (in the center) needs to equal the number of teeth in the ring (outside) divided by the number of planets (orbiting, in the middle). So far so good.

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Full-Color Edge-Lit Laser Cut Acrylic

Edge-lit art has been around for a very long time, and most people have probably come across it in a gift shop somewhere. All it takes is a pane of transparent material (usually an acrylic sheet) with the artwork etched into the surface. Shine a light into the sheet from the edge, and refraction takes over to light up the artwork. However, this technique is almost always limited to a single pane, and therefore a single color. [haqnmaq] wanted to take this idea and make it full-color, and has written up a great Instructables tutorial on how to accomplish this.

If you want to make something like this yourself, the only thing you really need is a laser cutter and some basic electronics equipment. The process itself is so straightforward that it’s surprising that it isn’t more common. You start by taking a photo of your choice and use an image editor to break it up into three photos, one for red, one for green, and one for blue. Each of those photos is then etched into an acrylic pane with a laser cutter. When the panes are positioned in front of each other and edge-lit with their respective LEDs, a full-color image comes to life.

This isn’t the first edge-lit artwork project we’ve featured, but it definitely has the highest fidelity. Because [haqnmaq’s] technique uses three colors, you can use his tutorial to reproduce any photo you like. You could even take this a step further and create animated photos by adding more panes and lighting them up in the correct sequence!

Wii-Motified Laser Cutter refocuses for Contoured Cutting

Still laser cutting all of your parts in 2D? Not the folks over at [Just Add Sharks]. With a few lines of code and an in-tact Wii-Mote, they’ve managed to rig their laser cutter to dynamically refocus based on the height of the material.

The hack is cleanly executed by placing the Wii-Mote both at a known fixed distance-and-angle and within line-of-sight of the focused beam. Thankfully, the image-processing is already done onboard by the Wii-Mote’s image sensor, which simply returns the (x,y) coordinates of the four brightest IR points in view. As the beam moves over the material, the dot moves up or down in the camera’s field-of-view, triggering a refocus of the laser as it cuts. Given that the z-axis table needs to readjust with the contour, the folks at [Just Add Sharks] have slowed down the cutting speed. Finally, it’s worth noting that the Wii-Mote was designed to detect IR LEDs, not a 10600-nanometer laser beam, but we suspect that the Wii-Mote is receiving colors produced by the fluorescing material itself, not the beam. Nevertheless, the result is exactly the same–a dynamically refocusing laser!

Now that [Glowforge] has released a continuously-refocusing laser cutter implemented with stereoscopic cameras, it’s great to see the community following in their footsteps with a DIY endeavor. See the whole system in action after the break!

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Mass Effect Rubber Band Gun a Beauty to Be-holster

This Halloween, crafting most of your props and replicas wont be as easy as hitting “print.” This Mass Effect M-6 Carnifex Rubber Band Gun is the exception, though, and it’s all thanks to the detailed efforts of [eggfooyoung]. Like many others in childhood, [eggfooyoung] dreamed of sporting his own rubber-band gun. Year’s later, he’s made that dream a reality, and one for many others as well.

rubber_band_gun_internals

Mechanically, rubber-band guns, especially semi-automatic ones, are a finely tuned escapade into complex levers and joints. [eggfooyoung] took it upon himself to learn from the best in the craft, in this case, YouTube user [RBGuns] who has posted designes for numerous rubber band weapons. Overall, the M-6 Carnifex is a triumph of shared knowledge, as it’s an iteration of [RBGun’s] M9 build. [eggfooyoung’s] documentation is also everything we’d love to see in a weekend project: design files [PDF], detailed pictures documenting the step-by-step gluing process, and resources to dig more deeply into building your own rubber band guns.

Drawbacks of Laser Cut Delrin–and How to Slip Around Them

Welcome back to part II in this ensemble of techniques with laser-cut Delrin. Thanks for many of the great insights along the way in the comments. In this guide, I’d like to go over some of the more immediate kinks that come to mind when getting started with this material.

Sourcing Delrin Sheets

When it comes to shopping, there are a variety of suppliers to choose from, but there are a few key words and thoughts to keep in mind.

Names

First, Delrin, is the “brand name” that refers to the Acetal homopolymer. Variants may also be labeled, acetal or acetal homopolymer. Delrin’s natural color is a soft white, but dyes can take it into a range of other colors. Black and white are, by far, the most common, though.

Tolerances

In the previous guide, all of the examples were cut from a small range of sheet thicknesses (0.0625[in], 0.09375[in], and .125[in]) sourced from OnlineMetals. As the thickness of the sheet increases, the tolerances on the thickness rating will also become more loose. You might buy a .125[in] plate and find it to be .124[in] in some places and .126[in] in others. If you purchase a .250[in] sheet, however, you’ll find that it may vary as much as .126[in] oversize though!

Buy it Flat

Despite McMaster-Carr being my go-to solution for one-off prototypes where rapid build iterations trump BOM cost, I don’t recommend purchasing Delrin from them as their sheets don’t have a flatness rating and often gets shipped bent in (oddly sized) boxes. (Seriously, has anyone else gotten a few oddly-sized parts in a gigantic McMaster-box before?)

Internal Stresses

Extruded Delrin has internal stresses built up inside of the sheet. There are a variety of reasons why this could be the case, but my biggest hunch is that the extrusion process at the factory results in different parts of the sheets solidifying at different times as the sheet cools, possibly causing some parts of the sheet to tighten from the cooling before other gooier sections have yet to finish cooling. What this means for you is that as your part gets lased out of the sheet, you’re, in a sense, relieving that stress. As a result, the part that you cut–especially for thin sheets–may come out of the laser cutter slightly warped.

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