If you’re not a woodworker, you might not have heard of the “45-degree rule.” It goes like this: a clamp exerts a force that radiates out across a triangular region of the wood that forms a right angle — 45 degrees on each side of the clamp’s point of contact. So, to ensure that force is applied as evenly as possible across the entire glue joint, clamps should be spaced so that these force triangles overlap. It’s a handy rule, especially for the woodworker looking to justify the purchase of more clamps; you can never have too many clamps. But is it valid?
The short answer that [ari kardasis] comes up with in the video below is… sort of. With the help of a wonderfully complex array of strain gauges and a Raspberry Pi, he found that the story isn’t so simple. Each strain gauge lives in a 3D printed bracket that spaces the sensors evenly along the wood under test, with a lot of work going into making the test setup as stiff as possible with steel reinforcement. There were some problems with a few strain gauges, but once he sorted that out, the test setup went into action.
[ari] tested clamping force transmission through pieces of wood of various widths, using both hardwoods and softwoods. In general, he found that the force pattern is much broader than the 45-degree rule suggests — he got over 60 degrees in some cases. Softwoods seemed to have a somewhat more acute pattern than hardwoods, but still greater than the rulebook says. At the end of the day, it seems like clamp spacing of two board widths will suffice for hardwoods, while 1.5 or so will do for softwoods. Either way, that means fewer clamps are needed.
A lot of woodworking is seat-of-the-pants stuff, so it’s nice to see a more rigorous analysis like this. It reminds us a lot of some of the experiments [Matthia Wandel] has done, like load testing various types of woods and glues.
The key is a modified design based on the Kresling pattern, with each actuator having a specially-designed section (the colored triangles in the image above) that are designed to pop out under a certain amount of positive pressure, and remain stable after it has done so. This section holds its shape until a certain amount of negative pressure is applied, and the section pops back in.
Whether or not this section is popped out changes the actuator’s shape, therefore changing the way it deforms. This makes a simple actuator bi-stable and capable of different movements, using only a single pressure source. Stack up a bunch of these actuators, and with careful pressure control, complex movements become possible. See it in action in two short videos, embedded just below the page break.
This particular story on researchers successfully making yeast-free pizza dough has been making the rounds. As usual with stories written from a scientific angle, it’s worth digging into the details for some interesting bits. We took a look at the actual research paper and there are a few curious details worth sharing. Turns out that this isn’t the first method for yeast-free baking that has been developed, but it is the first method to combine leavening and baking together for a result on par with traditional bread-making processes.
Basically, a dough consisting of water, flour, and salt go into a hot autoclave (the header image shows a piece of dough as seen through the viewing window.) The autoclave pressurizes, forcing gasses into the dough in a process similar to carbonating beverages. Pressure is then released in a controlled fashion while the dough bakes and solidifies, and careful tuning of this process is what controls how the bread turns out.
With the right heat and pressure curve, researchers created a pizza whose crust was not only pleasing and tasty, but with a quality comparable to traditional methods.
How this idea came about is interesting in itself. One of the researchers developed a new method for thermosetting polyurethane, and realized that bread and polyurethane have something in common: they both require a foaming (proofing in the case of bread) and curing (baking in the case of bread) process. Performing the two processes concurrently with the correct balance yields the best product: optimized thermal insulation in the case of polyurethane, and a tasty and texturally-pleasing result in the case of pizza dough. After that, it was just a matter of experimentation to find the right balance.
The pressures (up to 6 bar) and temperatures (145° Celsius) involved are even pretty mild, relatively speaking, which could bode well for home-based pizza experimenters.
Necessity might be the mother of all invention, but we often find that inventions around here are just as often driven by expensive off-the-shelf parts and a lack of willingness to spend top dollar for them. More often than not, we find people building their own tools or parts as if these high prices are a challenge instead of simply shrugging and ordering them from a supplier. The latest in those accepting the challenge of building their own parts is [Advanced Tinkering] who needed a specialty pressure gauge for a vacuum chamber.
In this specific case, the sensor itself is not too highly priced but the controller for it was the deal-breaker, so with a trusty Arduino in hand a custom gauge was fashioned once the sensor was acquired. This one uses an external analog-to-digital converter to interface with the sensor with 16-bit resolution, along with some circuitry to bring the ~8 V output of the sensor down to the 5 V required by the microcontroller. [Advanced Tinkering] wanted a custom live readout as well, so a 3D printed enclosure was built that includes both an LCD readout of the pressure and a screen with a graph of the pressure over time.
Virtually any hobby has an endless series of rabbit holes to fall into, with new details to learn around every corner. This is true for beekeeping, microcontrollers, bicycles, and gardening (just to name a few), but those involved in the intricate world of coffee roasting and brewing turn this detail dial up to the max. There are countless methods of making coffee, all with devout followers and detractors alike, and each with its unique set of equipment. To explore one of those methods and brew a perfect espresso, [Eric] turned to his trusted 3D printer and some compressed gas cylinders.
An espresso machine uses high pressure to force hot water through finely ground coffee. This pressure is often developed with an electric pump, but there are manual espresso machines as well. These require expensive parts which can withstand high forces, so rather than build a heavy-duty machine with levers, [Eric] turned to compressed CO2 to deliver the high pressure needed.
To build the pressure/brew chamber, he 3D printed most of the parts with the exception of the metal basked which holds the coffee. The 3D printed cap needs to withstand around nine atmospheres of pressure so it’s reasonably thick, held down with four large bolts, and holds a small CO2 canister, relief valve, and pressure gauge.
To [Eric]’s fine tastes, the contraption makes an excellent cup of coffee at minimal cost compared to a traditional espresso machine. The expendable CO2 cartridges only add $0.15 to the total cost of the cup and for it’s simplicity and small size this is an excellent trade-off. He plans to improve on the design over time, and we can’t wait to see what he discovers. In the meantime, we’ll focus on making sure that our beans are of the highest quality so they’re ready for that next espresso.
To understand where this all came from, you’ll have to dial back to [Matthias]’s first video, where he was just trying to make a simple corkboard. In an effort to get even pressure over the whole surface of the board, he came up with a shop-expedient vacuum clamp, made from a sheet of thick plastic, some scraps of wood and clamps, and a couple of vacuums. With the workpiece sandwiched between a smooth, flat table and the plastic sheet, he was able to suck the air out and apply a tremendous amount of force to the corkboard.
The comments to the first video led to the one linked below, wherein [Matthias] aimed to explore some of the criticisms of his approach. Using a quartet of BMP280 pressure sensor breakout boards and a Raspberry Pi, he was able to nicely chart the pressure inside his clamping jig. He found that not only did the sensors make it easy to find and fix leaks, they also proved that adding a porous layer between the workpiece and the vacuum bag wouldn’t likely improve clamping. He was also able to show which of his collection of vacuums worked best — unsurprisingly, the Miele sucked the hardest, although he found that it wasn’t suitable for continuous clamping duty.
Corralling electrons is great and what most of us are pretty good at, but the best projects have some kind of interface to the real world. Often, that involves some sort of fluid such as water or air moving through pipes. If you don’t grasp hydraulics intuitively, [Practical Engineering] has a video you’ll enjoy. It explains how flow and pressure work in pipes.
Granted, not every project deals with piping, but plumbing, sprinkler systems, cooling systems, and even robotics often have elements of hydraulics. In addition, as the video points out, fluid flow in a pipe is very similar to electrical current flowing through wires.