Knives Hewn from Brake Discs Past

Knives are tools that rely heavily on material quality to do their job right. A knife made of cheap steel won’t hold an edge well, and blunt knives are more likely to cause injury, or at the least, be more difficult to use. The trick to making a good knife is to start with good material. Disc brakes just so happen to be a great source of cast iron, and are readily available, so [Diesineveryfilm Customs] has machined a knife out of a brake disc.

The first step is to roughly cut out the knife’s form from the disc. It’s easy enough to cut out with an angle grinder, following up with a belt sander to finish up the grip. After sharpening, the sharp blade is taped off for safety while a wooden grip is added. Holes are drilled in the brake rotor, allowing the wooden parts to be pinned and glued together before a trip to the belt sander for shaping. A string and dye are added to the handle as finishing touches.

It’s a great use of high-quality scrap material to produce a useful tool. An earlier disc brake knife video shares some useful techniques of its own – we liked the shortcut of measuring the disc thickness, then using a matching drillbit to mark the centerline for sharpening.

Perhaps your own knives aren’t sharp enough – check out this home-built adjustable sharpening rig.

Home-Made Metal Brake

Sometimes, the appropriate application of force is the necessary action to solve a problem. Inelegant, perhaps, but bending a piece of metal with precision is difficult without a tool for it. That said, where a maker faces a problem, building a solution swiftly follows; and — if you lack a metal brake like YouTuber [makjosher] — building one of your own can be accomplished in short order.

Drawing from numerous online sources, [makjosher]’s brake is built from 1/8″ steel bar, as well as 1/8″ steel angle. The angle is secured to a 3/4″ wood mounting plate. Displaying tenacity in cutting all this metal with only a hacksaw, [makjosher] carved slots out of the steel to mount the hinges, which were originally flush with the wood. He belatedly realized that they needed to be flush with the bending surface. This resulted in some backtracking and re-cutting. [Makjosher] then screwed the pivoting parts to the wood mount. A Box tube serves as a handle. A coat of paint  finished the project, and adding another tool to this maker’s kit.

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Aluminum bending tutorial and a DIY brake

What makes a project really exceptional? Part of it is a, ‘gee, that’s clever’ angle with a little bit of, ‘that’s actually possible.’ One thing the Hack a Day crew really appreciates is awesome enclosures. Altoids tins will get you far, but to step up to the big leagues you’ve got to bend some aluminum. Luckily, [Rupert] sent in a great tutorial on bending aluminum sheets for enclosures.

To make his press brake, [Rupert] scavenged a few pieces of 38mm bamboo worktop scraps. After assembling a few of these pieces with some hinges, he was ready to bend some aluminum.

One trick [Rupert] picked up is scoring the sheet metal on the inside of a future bend. For [Rupert]’s project, he sent his 3mm aluminum sheet through a table saw set to cut 1mm deep. Of course this should only be done with a blade designed for non-ferrous metals with as many carbide teeth as possible. Judging from [Rupert]’s homebuilt Hi-Fi that used this construction technique, the results are phenomenal.

Motor drivers: half h-bridge with brake and more

Here’s a nice little circuit that will drive a motor and allow you to stop its rotation, giving your robot a set of brakes. It’s part of [JM’s] post about the in’s and out’s of building microcontroller friendly motor controllers (translated).

This particular setup is a half H-bridge. It allows you to drive the motor in one direction only. The MOSFET used on the ground-side of the motor doesn’t actually need to be there. This is the brake which let you electronically stop the motor from spinning. Without it, the motor will keep turning under its own momentum when the half-bridge is shut off. Depending on the application this can be a big problem. There’s a great demonstration of the circuit braking a fast spinning motor in the video clip below the fold.

It is possible to use this driver with PWM, but [JM] has some warnings about inbuilt functions like FastPWM. Make sure you read his admonition, and if you need a refresher don’t miss this Hackaday video segment.

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