At the end of the day, all it takes to make a guitar go to eleven is a new knob. Making the knob is another thing — that takes a shop full of machine tools, the expertise to use them, and a whole bunch of time. Then again, if you’re pressed for time, it looks like a 3D printer will do nicely too.
While the 3D printing route is clearly the easier option, it sure seems as if [Chronova Engineering] is more about the journey than the destination. In need of some knob bling for an electric guitar, he takes us through the lengthy process (nicely summarized in the video below) of crafting one from a bar of solid brass. Like all good machining projects, this one starts with making the tools necessary to start the actual build; in this case, it’s a tool to cut the splines needing to mate with the splines on the guitar’s potentiometer shaft. That side quest alone represents probably a third of the total effort on this project, and results in a tool that’s used for all of about 30 seconds.
Aside from spline cutting, there are a ton of interesting machining tidbits on display here. We particularly liked the use of a shaping technique to form the knurling on the knob, as opposed to a standard rotary method, which would have been difficult given the taper on the knob body. Also worth noting are the grinding step that puts a visually interesting pattern on the knob’s top surface, as well as the pantograph used to etch the knob’s markings.
Congrats to [Chronova Engineering] for a great-looking build, and the deep dive into the machinist’s ways. If you’re still interested in custom brass knobs but don’t have a machine shop, we can help with that.
Quick, what’s 360 divided by 23? It’s easy enough to get the answer, of course, but if you need to machine a feature every 15.652 degrees around a shaft, how exactly would you accomplish that? There are a number of ways, but they all involve some degree of machining wizardry. Or, you can just make the problem go away with a little automation.
The story behind [Tony Goacher]’s Rotary Table Buddy begins with some ATV tracks he got off AliExpress. His idea is to build a specialty electric vehicle for next year’s EMF Camp. The tracks require a splined shaft to drive them, which would need to be custom-made on a milling machine. A rotary table with a dividing plate — not as fancy as this one, of course –is usually the answer, but [Tony] was a little worried about getting everything set up correctly, so he embarked on a tactical automation solution to the problem.
An RP2040 provided the brains of the project, while a NEMA 23 stepper provides the brawn. [Tony] whipped up a quick PCB and 3D printed a case for the microcontroller, a stepper driver, an LCD display, and a few buttons. He 3D printed an adapter and a shaft coupler to mount the stepper motor to a rotary table. From there it was just a matter of coming up with a bit of code to run everything.
There’s a brief video in [Tony]’s blog post that shows Rotary Table Buddy in action, indexing to the next position after cutting one of the 23 splines. He says it took about ten minutes to cut each spline using this setup, which probably makes to total cutting time far less than the amount of time invested in the tool. But that’s hardly the point, and besides, now he’s set up for all kinds of machining operations in the future.
And we sure hope we hear about the EMF Camp build, too.
Rotary potentiometers, switches, and encoders all share a basic design: adjustment is done via a shaft onto which a knob is attached, and knobs are sold separately. That doesn’t mean one knob fits all; there are actually a few different standards. But just because knobs are inexpensive and easily obtained doesn’t mean it’s not worth making your own.
Why bother 3D printing your own knobs instead of buying them? For one thing, making them means one can rest assured that every knob matches aesthetically. The ability to add custom or nonstandard markings are another bonus. Finally, there’s no need to re-invent the wheel, because [Tommy]’s guide to making your own knobs has it all figured out, with the OpenSCAD script to match.
By default, [Tommy]’s script will generate a knob with three shims (for interfacing to a splined shaft) when pot_knob(); is called. The number of shims can be adjusted by modifying potKnobDefaultShimCount. To give the knob a flat side (to interface with D-shafts), change flatted = false to flatted = true. And for adding a screw insert suitable for a set screw? Change tightenerDiameter = 0 from zero to the diameter desired.
3D printers are good for a lot of things, but making parts for power transmission doesn’t seem to be one of them. Oh sure, some light-duty gears and timing belt sprockets will work just fine when printed, but oftentimes squooshed plastic parts are just too compliant for serious power transmission use.
But that’s not a hard and fast rule. In fact, this 3D-printed strain-wave transmission relies on the flexibility of printed parts to work its torque amplification magic. In case you haven’t been briefed, strain-wave gearing uses a flexible externally toothed spline nested inside an internally toothed stationary gear. Inside the flexible spline is a wave generator, which is just a symmetrical cam that deforms the spline so that it engages with the outside gear. The result is a high ratio gear train that really beefs up the torque applied to the wave generator.
It took a couple of prototypes for [Brian Bocken] to dial in his version of the strain-wave drive. The PLA he used for the flexible spline worked, but wasn’t going to be good for the long haul. A second version using TPU proved better, but improvements to the motor mount were needed. The final version proved to pack a punch in the torque department, enough to move a car. Check it out in the video below.
Strain-wave gears have a lot of applications, especially in robotic arms and legs — very compact versions with the motor built right in would be great here. If you’re having trouble visualizing how they work, maybe a Lego version will clear things up.
Lathes are usually used to turn metal, but internal keyways and splines are operations often performed with a broach. An older tool called a shaper would be perfect here, but shapers are relatively rare these days — or are they? There are many examples of shaper attachments for lathes. These are human-powered devices that scrape a bit of metal off each pass. The lathe itself is used to keep the workpiece in place and move the tool in a repeatable way.
Rather than create a shaper jig from scratch, [John] decided to use his compound slide as the shaper slide itself. He removed the compound slide lead screw, which allowed the compound to slide freely. He then fabricated a double hinged bar and bolted this to the compound slide. Moving the bar causes the slide to move. Just add a cutting tool, and you’re ready to cut a keyway. Add an indexing plate, and you’re ready to cut a spline. You can see the tool in action after the break.
Do you like change for the sake of change? Are you incapable of leaving something in a known and working state, and would rather fiddle endlessly with it? Are you unconcerned about introducing arbitrary compatibility issues into your seemingly straight-forward product line? If you answered “Yes” to any of those questions, have we got the job for you! You can become a product engineer, and spend your days confounding customers who labor under the unrealistic expectation that a product they purchased in the past would still work with seemingly identical accessories offered by the same company a few years down the line. If interested please report to the recruitment office, located in the darkest depths of Hell.
Until the world is rid of arbitrary limitations in consumer hardware, we’ll keep chronicling the exploits of brave warriors like [Alex Whittemore], who take such matters into their own hands. When he realized that the blades for his newer model Ninja food processor didn’t work on the older motor simply because the spline was a different size, he set out to design and print an adapter to re-unify the Ninja product line.
[Alex] tried taking a picture of the spline and importing that into Fusion 360, but in the end found it was more trouble than it was worth. As is the case with many printed part success stories, he ended up spending some intimate time with a pair of calipers to get the design where he wanted it. Once broken down into its core geometric components (a group of cylinders interconnected with arches), it didn’t take as long as he feared. In the end the adapter may come out a bit tighter than necessary depending on the printer, but that’s nothing a few swift whacks with a rubber mallet can’t fix.
This project is a perfect example of a hack that would be much harder (but not impossible) without having access to a 3D printer. While you could create this spline adapter by other means, we certainly wouldn’t want to. Especially if you’re trying to make more than one of them. Small runs of highly-specialized objects is where 3D printing really shines.
The twenty best projects will receive $100 in Tindie credit, and for the best projects by a Student or Organization, we’ve got two brand-new Prusa i3 MK3 printers. With a printer like that, you’ll be breaking stuff around the house just to have an excuse to make replacement parts.