It used to be that when we featured one of [Frank Olson]’s DIY ribbon microphone builds, it was natural to focus on the fact that he was building them almost exclusively from wood. But despite how counterintuitive it may seem, and for as many comments as we get that his microphones shouldn’t work without metal in the ribbon motors, microphones like this wooden RCA Model 77 reproduction both look and sound great.
But ironically, this homage features a critical piece that’s actually not made of wood. The 77’s pickup pattern was cardioid, making for a directional mic that picked up sound best from the front, thanks to an acoustic labyrinth that increased the path length for incoming sound waves. [Frank]’s labyrinth was made from epoxy resin poured into a mold made from heavy paper, creating a cylinder with multiple parallel tunnels. The tops and bottoms of adjacent tunnels were connected together, creating an acoustic path over a meter long. The ribbon motor, as close to a duplicate of the original as possible using wood, sits atop the labyrinth block’s output underneath a wood veneer shell that does its best to imitate the classic pill-shaped windscreen of the original. The video below, which of course was narrated using the mic, shows its construction in detail.
If you want to check out [Frank]’s other wooden microphones, and you should, check out the beautiful Model 44 replica that looks ready for [Sinatra], or the Bk-5-like mics he whipped up for drum kit recording.
Not too many people build their own microphones, and those who do usually build them out of materials like plastic and metal. [Frank Olson] not only loves to make microphones, but he’s also got a thing about making them from wood, with some pretty stunning results.
[Frank]’s latest build is a sorta-kinda replica of the RCA BK-5, a classic of mid-century design. Both the original and [Frank]’s homage are ribbon microphones, in which a thin strip of corrugated metal suspended between the poles of magnets acts as a transducer. But the similarities end there, as [Frank] uses stacked layers of walnut veneer as the frame of his ribbon motor. The wood pieces are cut with a vinyl cutter, stacked up, and glued into a monolithic structure using lots of cyanoacrylate glue. The video below makes it seem easy, but we can imagine getting everything stacked neatly and lined up correctly is a chore, especially when dealing with neodymium magnets. Cutting and corrugating the aluminum foil ribbon is no mean feat either, nor is properly tensioning it and making a solid electrical contact.
Research activity into 3D printing never seems to end, with an almost constant stream of new techniques and improvements upon old ones hitting the news practically daily. This time, the focus is on a technique we’ve not covered so much, namely binder jetting additive manufacturing (BJAM for short, catchy huh?) Specifically the team from Oak Ridge National Laboratory, who have been exploring the use of so-called hyperbranched Polyethyleneimine (PEI) as a binder for jetting onto plain old foundry silica sand (nature, free access.)
The PEI binder was mixed with a 75:25 mix of water and 1-propanol (not to be mixed up with 2-propanol aka isopropanol) to get the correct viscosity for jetting with a piezoelectric print head and the correct surface tension to allow adequate powder bed penetration, giving optimal binding efficiency. The team reported a two-fold increase in strength over previous jetting techniques, however, the real news is what they did next; by infusing the printed part (known as the green part) with common old ethyl cyanoacrylate (ECA, or super glue to us) the structural strength of the print increased a further eight times due to the reaction between the binder and the ECA infiltrate.
To further bestow the virtues of the PEI binder/ECA mix, it turns out to be water-soluble, at least for a couple of days, so can be used to make complex form washout tooling — internal supports that can be washed away. After a few days, the curing process is complete, resulting in a structure that is reportedly stronger than concrete. Reinforce this with carbon fiber, and boy do you have a tough building material!
Not bad for some pretty common materials and a simple printing process.
We’ve all encountered the odd plastic part that is broken and unobtainable. Sure, 3D printers can print big replacement parts, but sometimes you just need to rebuild a very specific piece. [AkBkukU] shows off a technique for doing just that using a process you could almost call manual 3D printing. We’ve seen baking soda used to cure cyanoacrylate glue before, but this technique uses it to build layers of glue that are apparently quite solid.
There’s quite a bit of nuance in the video below, but the basic idea is to put a pile of soda on one side of a piece of tin foil and a glob of glue. You dip the part in glue and then into the soda. Each time you get a little thicker layer of glue.
Afterward, you’ll have to file and otherwise shape the new part, but the fact that it can survive being filed should tell you something. We were reminded of how some people use epoxy to form repair parts and then machine them to the exact shape needed. At the very end of the video he builds up layers on a part he can’t dip. Did it work? Watch it and see.
In addition to the manual 3D printing technique, he demonstrates using baking soda to cure repairs on a knurled knob from an old clock radio. That’s a bit more conventional, but if you haven’t seen it done before, it is nearly miraculous.
Simple clamps are great if you need to keep the pressure on two parallel surfaces, but if you have an irregular plane, or you need to cut through it, clamps are not the correct tool. The folks at [NYC CNC] feature a video with a clever hack borrowing from other disciplines. Painters tape is applied to the top of a level mounting surface in the machine and then burnished. The same is done to the bottom of the workpiece. Superglue is drizzled between the tape layers and pressed together so now the stock is held firmly below the toolhead.
Some parts are machined in the video, which can be seen below, and the adhesion holds without any trouble. One of the examples they cut would be difficult to hold without damage or stopping the machine. The accepted wisdom is that superglue holds well to a slightly porous surface like tape, but it doesn’t like do as well with smooth surfaces like metal. Removing residue-free tape at the end of a cut is also cleaner and faster than glue any day.
When I first started getting into 3D printed projects that would require final assembly from multiple parts, I wanted to make sure I had an adhesive that would really hold up. I couldn’t imagine anything worse than spending 10’s of hours printing and assembling something, only to have it fall apart because my adhesive wasn’t up to the task. So I spent a lot of time trolling 3D printing message boards and communities trying to find the best way of gluing PLA. It should come as no surprise that, like everything else in the world, there are a ridiculous number of opinions on the subject.
If you’re printing with ABS, the general wisdom is that solvent welding with acetone is the best bet. You put some acetone on the printed parts, rub them together, and the plastic fuses together. This happens because the ABS melts slightly when exposed to the acetone, so they end up essentially melding into one piece. This sounded like exactly what I wanted, but unfortunately, acetone doesn’t have this same effect on PLA.
After some more research I found people suggesting Weld-On #16, an acrylic adhesive that will actually melt PLA. A little of this applied to the parts, they said, and you can solvent weld PLA just like acetone on ABS. Sure enough, the stuff works great and I’ve used it to put together nearly everything I’ve printed in PLA over the last few years. Only problem is, this stuff is a bit nasty, takes 24 hours to fully cure, and nobody has it locally.
So as an experiment I thought I’d take a look at a few adhesives sold at the local big box retailer and see if I couldn’t find something comparable. Do I need to keep ordering this nasty goop online every time, or can I pick something up off the shelf? More to the point, is solvent welding PLA really any better than just gluing it?
Hackers tend to stash away lots of stuff that seems useless, right up until it saves the day. This includes not just junk in our parts bin but brains full of tips and tricks for the shop. With that in mind, you might want to file away a few of the tips in [AvE]’s video of how he made bulletproof glass for a rainy day.
By his own admission, [AvE]’s video is a little disjointed, and the topic of the bulletproof glass is only covered at the beginning and again briefly at the end. Most of the video concerns the machining of a stout stand for the glass for testing on the range. There’s plenty to learn from the machining, though, and [AvE] is always good for a laugh, so the video is worth a watch. The bulletproof glass itself is part of a long-term project that [AvE] is releasing first to his Patreon patrons – a ridiculously over-built flashlight dubbed “The Midnight Sun”. His first two tries at laminating the Lexan discs were less that optimal, as both brands of cyanoacrylate glue clouded the polycarbonate. Stay tuned to the end of the video for the secret of welding Lexan together into an optically clear sandwich.
As for testing under fire, [AvE] sent the rig off to buddy [TAOFLEDERMAUS] for the hot lead treatment. The video after the break shows that the glass is indeed bulletproof, as long as the bullet in question is a .22LR. Not so much for the 9mm, though – that was a clear punch-through. Still, pretty impressive performance for homebrew.