Stronger 3D Prints — Glue Or Carbon Fiber?

[CNCKitchen], like many others, is looking to make strong 3D prints. Using a high tech PLA bio copolyester compound, he printed a bunch of hooks in two different orientations. He used several different types of glue including epoxy and superglue. You can see the video of his results, below.

In addition to the glue, he used epoxy and bulk carbon fiber, again, in two different orientations. After several days of curing, he was ready to test.

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Fail Of The Week: Taking Apart A Tesla Battery

It takes a lot of energy to push a car-sized object a few hundred miles. Either a few gallons of gasoline or several thousand lithium batteries will get the job done. That’s certainly a lot of batteries, and a lot more potential to be unlocked for their use than hurling chunks of metal around on wheels. If you have an idea for how to better use those batteries for something else, that’s certainly an option, although it’s not always quite as easy as it seems.

In this video, [Kerry] at [EVEngineering] has acquired a Tesla Model 3 battery pack and begins to take it apart. Unlike other Tesla batteries, and even more unlike Leaf or Prius packs, the Model 3 battery is extremely difficult to work with. As a manufacturing cost savings measure, it seems that Tesla found out that gluing the individual cells together would be less expensive compared to other methods where the cells are more modular and serviceable. That means that to remove the individual cells without damaging them, several layers of glue and plastic have to be removed before you can start hammering the cells out with a PEX wedge and a hammer. This method tends to be extremely time consuming.

If you just happen to have a Model 3 battery lying around, [Kerry] notes that it is possible to reuse the cells if you have the time, but doesn’t recommend it unless you really need the energy density found in these 21700 cells. Apparently they are not easy to find outside of Model 3 packs, and either way, it seems as though using a battery from a Nissan Leaf might be a whole lot easier anyway.

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Saving Your Vision From Super Glue In The Eyes

Super glue, or cyanoacrylate as it is formally known, is one heck of a useful adhesive. Developed in the 20th century as a result of a program to create plastic gun sights, it is loved for its ability to bond all manner of materials quickly and effectively. Wood, metal, a wide variety of plastics — super glue will stick ’em all together in a flash.

It’s also particularly good at sticking to human skin, and therein lies a problem. It’s bad enough when it gets on your fingers. What happens when you get super glue in your eyes?

Today, we’ll answer that. First, with the story of how I caught an eyeful of glue. Following that, I’ll share some general tips for when you find yourself in a sticky situation.

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Epoxy Too Thin? Use Wood Flour As A Thixotropic Filler

The world of glues is wide and varied, and it pays to use the right glue for the job. When [Eric] needed to stick a wide and flat 3D printed mount onto the back of a PCB that had been weatherproofed with an uneven epoxy coating, he needed a gap-filling adhesive that would bond to both surfaces. It seemed like a job for the hot glue gun, but the surface was a bit larger than [Eric] was comfortable using with hot glue for. The larger the surface to be glued, the harder it is to do the whole thing before hot glue cools too much to bond properly.

What [Eric] really wanted to use was a high quality two-part epoxy that he already had on hand, but the stuff was too runny to work properly for this application. His solution was to thicken it with a thixotropic filler, which yields a mixture that is akin to peanut butter: sticky, easily spread to where it’s needed, but otherwise stays in place without dripping or sagging and doesn’t affect bonding.

3D printed pad stuck to back of PCB with thickened epoxy.

Common thixotropic fillers include ground silica or plastic fibers, but [Eric]’s choice was wood flour. Wood flour is really just very fine sawdust, and easily obtained from the bag on his orbital sander. Simply mix up a batch of thin two-part epoxy and stir in some wood flour until the sticky mixture holds its shape. Apply as needed, and allow it to cure.

Thanks to this, [Eric] was able to securely glue a 3D printed pad to the back of his animated LED snowflakes to help mount them in tricky spots. Whether for small projects or huge installations, LEDs, PCBs, and snowflakes are a good combination.

3D-Printer Extrudes Paper Pulp Instead Of Plastic

We’ve seen all sorts of 3D-printers on these pages before. From the small to the large, Cartesians and deltas, and printers that can squeeze out plastic, metal, and even concrete. But this appears to be the first time we’ve ever featured a paper-pulp extruding 3D-printer.

It’s fair to ask why the world would need such a thing, and its creator, [Beer Holthuis], has an obvious answer: the world has a lot of waste paper. Like 80 kg per person per year. Thankfully at least some of that is recycled, but that still leaves a lot of raw material that [Beer] wanted to put to work. Build details on the printer are sparse, but from the photos and the video below it seems clear how it all went together. A simple X-Y-Z gantry moves a nozzle over the build platform. The nozzle, an order of magnitude or two larger than the nozzles most of us are used to, is connected to an extruder by a plastic hose. The extruder appears to be tube with a stepper-driven screw that lowers a ram down onto the pulp, squeezing it into the hose. [Beer] notes that the pulp is mixed with a bit of “natural binder” to allow the extruded pulp to keep its shape. We found the extrusion process to be just a wee bit repulsive to watch, but fascinating nonetheless, and the items he’s creating are certainly striking in appearance.

This may be the first pulp printer to grace our pages, but it’s not the first pulp hack we’ve featured. Pulp turns out to be a great material to keep your neighbors happy and even makes a dandy fuel.

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Sharpies And Glue Sticks Fight The Gummy Metal Machining Blues

“Gummy” might not be an adjective that springs to mind when describing metals, but anyone who has had the flutes of a drill bit or end mill jammed with aluminum will tell you that certain metals do indeed behave in unhelpful ways. But a new research paper seeks to shed light on the gummy metal phenomenon, and may just have machinists stocking up on office supplies.

It’s a bit counterintuitive that harder metals like steel are often easier to cut than softer metals; especially aluminum but also copper, nickel alloys, and some stainless steel alloys. But it happens, and [Srinivasan Chandrasekar] and his colleagues at Purdue University wanted to find out why, and what can be done about it. So the first job was to get up close and personal with the interface between a cutting tool and metal stock, to observe the dynamics of cutting. In a fascinating bit of video, they saw that softer metals tend to fold in sinuous patterns rather than breaking on defined shear planes.

Source: American Physical Society.

Having previously noted that cutting through Dykem, a common machinist’s marking fluid, changes chip formation in soft metals, the researchers tested everything from Sharpies to adhesive tape and even correction fluid, and found that they all helped to reduce the gumming action to some degree. Under their microscope they can clearly see that chips form differently once the cutting edge hits the treated surface, tending to act more brittle and ejecting rather than folding. They also noted a marked decrease in cutting force for the treated metal, and much-improved surface finish to boot.

Will Sharpies and glue sticks enter the book of old machinist’s tricks like gauge-block wringing? Only time will tell. But for now, this is a pretty fascinating bit of research that you might be able to put to the test in your shop. Let us know what you find in the comments.

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A Slightly Scientific Examination Of Epoxies

Two-part epoxy is one of those must-have items in your toolbox, albeit kept in a ziploc bag to keep all that goo off the rest of your tools. It’s a glue with a million uses, but which brand is best? Should you keep some cheap five-minute epoxy around, or should you splurge for the fancy, long-setting JB Weld. It’s not a perfect analysis, but at least [Project Farm] has done the experiment. This is a test of which two-part epoxy you can find at your local home supply store is strongest.

The epoxies tested include Gorilla epoxy, Devcon Plastic Steel, Loctite Epoxy Weld, JB Weld original, JB Weld Kwik Weld, and JB ExtremeHeat. This more or less covers the entire gamut of epoxies you would find in the glue aisle of your local home supply store; the Gorilla epoxy is your basic 5-minute epoxy that comes in a double barrel syringe, and the JB Welds are the cream of the crop.

The testing protocol for this experiment consisted of grinding a piece of steel clean, applying a liberal blob of each epoxy, and placing three bolts, head down, in each puddle. The first test was simply suspending weights in 2.5-pound increments to each bolt as a quick test of shear strength. Here, the losers in order were the JB Weld ExtremeHeat, JB Weld KwikWeld, Loctite, Gorilla Epoxy, Devcon Plastic Steel, and finally the JB Weld Original. Your suspicions are confirmed: those fancy new versions of JB Weld aren’t as good as the original. The fact that they’re worse than 5-minute epoxy is surprising, though. The second test — torquing the bolts out of the epoxy — gave similar results, with Devcon Plastic Steel beating the JB Weld Original just barely.

So, what do these results tell us? Cheap five-minute epoxy isn’t terrible, and actually better than the fancy new versions of JB Weld. Loctite is okay, and the Devcon and original JB Weld are at the top of their game. That’s not that surprising, as you can cast cylinder heads for engines out of JB Weld.

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