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.

Turn Your New Years Resolution Into a Belt Grinder

We’re just over a month into the new year, and some people’s resolve on those exercise plans are already dwindling. There’s some good news though. That treadmill can be hacked into a nice belt grinder for your shop.

[Bob]’s treadmill belt grinder is based on a 2.5 horsepower motor he salvaged from a broken, donated treadmill. This motor needs 130 VDC to run, which is a bit of a challenge to generate. Fortunately, lots of treadmills seem to use the same MC-60 motor controller, which is compatible with this motor. Due to the widespread use of this controller, they can be found on eBay for about $30.

With the motor spinning, [Bob] built up a frame for the grinder, added rollers to hold the belt, and a spring based belt tensioner. The motor’s speed set point is controlled by a potentiometer, and the controller varies the power to keep a constant speed. Since the motor is capable of some serious RPM, a tachometer was added for feedback to prevent high-speed belt shredding.

The final result is a very professional looking tool for under $200. What would a grinder like this be used for? Knives of course! 2″ belt grinders are perfect for shaping and grinding knives and swords. In fact, you can see one in use in this sword hack.

Check out a video of the build after the break.

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The Most Sensational Calipers On The Planet!

Everyone here probably has a pair of cheap Chinese calipers kicking around the workbench. This means everyone here also knows how quickly the batteries in these handy little tools die. [Thosnbn] also noticed this, but instead of simply complaining and wishing the problem would go away, he decided to do something about it. He built a battery pack for his calipers, giving this tool a two year battery life.

The idea for this build came after [thosnbn]  completely destroyed a pair of these cheap calipers. At the time, the fix was to tape a AA battery to the tool, and solder wires directly to the contact pads for the tiny button cell battery. This fix worked, and after dealing with the ugliest tool known to man for a few years, [thosnbn] decided to clean it up a little.

The new battery enclosure was designed in Fusion360, includes handy features like a switch, and is completely 3D printed. It took a few weeks for [thosnbn] to get all the parts to fit together correctly, but the end result is great. This battery pack fits neatly on the back of the calipers, holds a single AA battery, and the lid is tightly secured with a pair of machine screws.

Unfortunately, [thosnbn] chose to share this project on imgur, a site that does not support sharing .stl or other 3D printer files. It does, however, serve as inspiration for you to make your own battery pack for a pair of cheap calipers.

The Mother Of All Paper Cuts

A Dremel is a fantastically handy tool to have around the workbench, but there is one glaring and obvious downside: you will always run out of cut-off discs. if you’re trying to break into a fancy snap-fit enclosure that has been inexplicably glued together, you’ll invariably need to run down to the hardware store to shell out some cash for a tiny tube of cut-off disks.

[KB9RLW] has the answer to this problem. He’s cutting wood and plastic with paper discs spinning at 35,000 RPM.

The paper used for this application is just a piece of junk mail or heavy, probably glossy card stock. After poking a hole in this piece of paper, tracing a circle with a homemade compass, and cutting out the cutting disk with a pair of scissors, this cut-off disc is easily mounted in the standard Dremel mandrel.

The test cut [KB9RLW] shows us is on a plastic wall wart that’s a glued together, snap-fit mess. The paper cut-off wheel makes short work of this nigh-impenetrable brick of plastic, revealing the electronic goodies inside. This cut-off wheel will also cut through small bits of wood, like a bit of molding.

After cutting halfway through the wooden molding, the paper disc quickly disintegrates — this is the same behavior we last year when this trick was being used on a table saw. But any home should get more than enough junk mail for a steady supply of paper Dremel cut-off discs. While this new attachment for your fancy rotary tool won’t last very long, it is a very expedient way to get into bits of electronics without paying Dremel several cents for a cut-off disc.

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Good in a Pinch: The Physics of Crimped Connections

I had a friend who was an electronics assembly tech for a big defense contractor. He was a production floor guy who had a chip on his shoulder for the engineers with their fancy book-learnin’ who couldn’t figure out the simplest problems. He claimed that one assembly wasn’t passing QC and a bunch of the guys in ties couldn’t figure it out. He sidled up to assess the situation and delivered his two-word diagnosis: “Bad crimp.” The dodgy connector was re-worked and the assembly passed, much to the chagrin of the guys in the short-sleeved shirts.

Aside from the object lesson in experience sometimes trumping education, I always wondered about that “bad crimp” proclamation. What could go wrong with a crimp to so subtly futz with a circuit that engineers were baffled? How is it that we can rely on such a simple technology to wire up so much of the modern world? What exactly is going on inside a crimped connection anyway?

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Metalworking Hacks Add Functionality to Snap-On Tool Chest

Problem: you’re a student mechanic and you’ve already poured a ton of money into a Snap-On roller cabinet loaded with the tools of the trade, but you still need sensible storage for your cordless tools. Solution: a DIY version of Snap-On’s PowerCab cordless tool station at a fraction of the cost.

rnqvgsoMechanics seem to have a love-hate relationship with Snap-On tools. Some love the brand, others hate it, but the majority seem to hate that they love the tools. It sounds like [GenTQ] reached her limit on brand loyalty when even her 50% student discount wasn’t enough to entice her to add Snap-On’s admittedly very cool KRL1099 cabinet for cordless drivers and chargers. So it was off to Harbor Freight for their seven-drawer side cabinet for less than $200. The cabinet was gutted of drawers, a frame for the new slide-out was welded up, and sheet steel was fabricated into organizer shelves and a new drawer front. A power strip and drag-chain were added to feed the chargers, and the new drawer went off to the powder coater for a matching paint job.

It may not have the Snap-On badge, and purists may cringe at the mixed-marriage with Horror Fright, but we like the results just fine. And she saved something like $1200 in the process. We think Harbor Freight gets a bad rap, deservedly so for some tools, but there are hidden gems amid the dross just ripe for the hacking, as [GenTQ] ably shows.

[via r/DIY]

Free Routing for gEDA

If you lay out PC boards using software, it is a good bet you have an opinion about autorouters. Some people won’t use a package that can’t automatically route traces. Others won’t accept a machine layout when they can do their own by hand. You can, of course, combine the two, and many designers do.

The open source gEDA PCB package (and pcb-md) have an autorouter, but it is pretty simplistic. [VK5HSE] shows how you can use a few tools to interface with the Java Freerouting application, to get a better result. For example, the original router made square corners, while the Freerouting application will create angles and arcs, if configured properly.

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