Analyzing CNC Tool Chatter With Audacity

January 16, 2020 by Dan Maloney 32 Comments

When you’re operating a machine that’s powerful enough to tear a solid metal block to shards, it pays to be attentive to details. The angular momentum of the spindle of a modern CNC machine can be trouble if it gets unleashed the wrong way, which is why generations of machinists have developed an ear for the telltale sign of impending doom: chatter.

To help develop that ear, [Zachary Tong] did a spectral analysis of the sounds of his new CNC machine during its “first chip” outing. The benchtop machine is no slouch – an Avid Pro 2436 with a 3 hp S30C tool-changing spindle. But like any benchtop machine, it lacks the sheer mass needed to reduce vibration, and tool chatter can be a problem.

The analysis begins at about the 5:13 mark in the video below, where [Zach] fed the soundtrack of his video into Audacity. Switching from waveform to spectrogram mode, he was able to identify a strong signal at about 5,000 Hz, corresponding to the spindle coming up to speed. The white noise of the mist cooling system was clearly visible too, as were harmonic vibrations up and down the spectrum. Most interesting, though, was the slight dip in frequency during the cut, indicating loading on the spindle. [Zach] then analyzed the data from the cut in the frequency domain and found the expected spindle harmonics, as well the harmonics from the three flutes on the tool. Mixed in among these were spikes indicating chatter – nothing major, but still enough to measure.

Audacity has turned out to be an incredibly useful tool with a broad range of applications. Whether it be finding bats, dumping ROMs, detecting lightning strikes, or cloning remote controls, Audacity is often the hacker’s tool of choice.

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Stacks Of Spring Washers Power The Drawbar On This CNC Mill Conversion

January 11, 2020 by Dan Maloney 25 Comments

With Tormach and Haas capturing a lot of the entry-level professional market for CNC machines, we don’t see too many CNC conversions of manual mills anymore. And so this power drawbar conversion for a Precision Matthews mill really caught our eye.

What’s that, you say? Didn’t [Physics Anonymous] already build a power drawbar for a mill? They did, and it was quite successful. But that was based on a pneumatic impact wrench, and while it worked fine on a manual mill, the same approach would be a bit slow and cumbersome on a CNC mill. For this build, they chose a completely different approach to providing the necessary upward force to draw the collet into the collet holder and clamp down on the tool: springs. Specifically, Belleville spring washers, which are shaped like shallow cups and can exert tremendous axial force over a very short distance.

[PA] calculated that they’d need to exert 2,700 pounds (12,000 Newtons) of force over a length of a couple of inches, which seems outside the Belleville washer’s specs. Luckily, the springs can be stacked, either nested together in “series” to increase the load force, or alternating in “parallel” to apply the rated force over a greater distance. To compress their stack, they used a nifty multi-stage pneumatic cylinder to squash down the springs and release the collet. They also had to come up with a mechanism to engage to machine’s spindle only when a tool change is called for. The video below details the design and shows the build; skip to 11:32 to see the drawbar in action.

We’re looking forward to the rest of [Physics Anonymous]’ conversion. They’re no strangers to modifying off-the-shelf machines to do their bidding, after all – witness their improvements to an SLA printer.

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Universal Interface Board Comes To The Rescue Of Bigger Projects

December 19, 2019 by Donald Papp 31 Comments

As soon as a project involves other assemblies, parts, or modules, things get more complicated. Devices like fans, cooling units, probes, pumps, or lighting might have simple electrical requirements, but they are rarely identical. As a result, one’s tidy project ends up having to deal with, for example, a pump that is controlled with 5 V active high logic, a sensor that outputs 5 V active low, lights that expect to be switched with 24 VDC, and a fan that needs a relay right now. But that might change in the future.

That’s exactly what led [Lukas Fässler] to design and build the Universal Interface, a board intended to be a kind of universal translator and interface for all such devices. The idea is to have one Universal Interface board for every external device. For each board, a wide variety of input combinations controls a single output. The boards are “hardware programmable” in the sense that jumpers (zero-ohm resistors) are used to spell out in black and white exactly what combinations of inputs result in which output state. In this way, some standardization and clarity of control can be enforced while still being flexible enough to accommodate changes.

Jumper-configured logic table defining with utter clarity which combination of inputs results in an OFF or ON.

Each Universal Interface board has three inputs and an enable line, each with their own indicator LED visually confirming its state. The inputs are 24 V tolerant and each can be configured with a pull-up, a pull-down, and as an active high or active low. There is one output, but it takes several forms: a sturdy relay, a powerful open-collector output, a 5 V logic output, and a 24 V logic output. Configuring which output state corresponds to what combination of inputs is set by jumpers, so the board is very much WYSIWYG.

[Lukas] is currently using four of these devices with his CNC mill project, all in different configurations, and they’re working reliably. Interested? The GitHub repository for the project has all the board design files.

Steel Tubes And Ground Plates Form The Skeleton Of This DIY Vertical CNC Mill

November 27, 2019 by Dan Maloney 29 Comments

If you’re going to do it yourself, you might as well outdo yourself. That seems to be the thinking behind this scratch-built CNC mill, and it’s only just getting started.

According to [Kris Temmerman], the build will cost about $10,000 by the time he’s done. So it’s not cheap, and a personal CNC from Tormach can be had for less, but that’s missing the point entirely. [Kris] built most of the structural elements for the vertical mill from cheap, readily available steel tubing, of the kind used for support columns in commercial buildings. Mounted to those are thick, precision-ground steel plates, which eat up a fair fraction of the budget. Those in turn hold 35 mm linear bearings and ball screws for the three axes, each powered by a beefy servo. The spindle is a BT30 with a power drawbar, belt-driven by an external motor that [Kris] doesn’t share the specs on, but judging from the way it flings chips during the test cut in the video below, we’d say it’s pretty powerful.

There’s still plenty to do, not least of which is stiffening the column; perhaps filling it with epoxy granite would do the trick? But it sure looks like [Kris] is building a winner here, and if he keeps the level of craftsmanship up going forward, he’ll have a top-quality machine on his hands.

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DIY CNC Router Uses Chains The Right Way

November 19, 2019 by Lewin Day 28 Comments

There are a million and one ways to build your own CNC router, depending on your tastes, budget, and application, your design choices will differ accordingly. [Steve Tyng] was well aware of this when undertaking his project, and built the machine that made sense for him.

[Steve’s] build has a strong focus on keeping costs down, and that’s reflected in the hardware used. Wanting a large work area of 30″ x 60″, off-the-shelf linear rails in 6 foot lengths were prohibitively expensive. Instead, 1″ angle iron was sourced from the local garden centre, and used in conjunction with steel v-bearings. It’s a lot cheaper, and good enough for the application at hand, so why not? Other smart choices abound, such as using an IKEA cabinet as the base, and a fanless computer to run the show to avoid death by dust.

When it came time to build the axes, there was plenty of roller chain on hand. Chain is usually passed up for options such as timing belts or ballscrews in the CNC community, as it tends to stretch over time and offers poor accuracy. However, [Steve] took stock of the drawbacks of the method, and made efforts to overcome these weak points in the design. The Y and X axes were specially designed to keep the chain supported along its length. This helped avoid the problem of long drooping chains and poor tension.

While it’s not an industrial-strength build with world-beating accuracy, it’s a solid CNC machine that can carve out large workpieces without issue. Over the years, we’ve seen plenty of DIY CNCs, built with everything from PVC pipe to welded steel. Video after the break.

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Jubilee: A Toolchanging Homage To 3D Printer Hackers Everywhere

November 14, 2019 by Sonya Vasquez 36 Comments

I admit that I’m late to the 3D printing game. While I just picked up my first printer in 2018, the rest of us have been oozing out beautiful prints for over a decade. And in that time we’ve seen many people reimagine the hardware for mischief besides just printing plastic. That decade of hacks got me thinking: what if the killer-app of 3D printing isn’t the printing? What if it’s programmable motion? With that, I wondered: what if we had a machine that just offered us motion capabilities? What if extending those motion capabilities was a first class feature? What if we had a machine that was meant to be hacked?

One year later, I am thrilled to release an open-source multitool motion platform I call Jubilee. For a world that’s hungry for toolchanging 3D printers, Jubilee might be the best toolchanging 3D printer you can build yourself–with nothing more than a set of hand tools and some patience. But it doesn’t stop there. With a standardized tool pattern established by E3D and a kinematically coupled hot-swappable bed, Jubilee is rigged to be extended by anyone looking to harness its programmable motion capabilities for some ad hoc automation.

Jubilee is my homage to you, the 3D printer hacker; but it’s meant to serve the open-source community at large. Around the world, scientists, artists, and hackers alike use the precision of automated machines for their own personal exploration and expression. But the tools we use now are either expensive or cumbersome–often coupled with a hefty learning curve but no up-front promise that they’ll meet our needs. To that end, Jubilee is meant to shortcut the knowledge needed to get things moving, literally. Jubilee wants to be an API for motion.

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Forget Printing Labels For Your Bathtub Hooch, Why Not Engrave The Bottle?

November 2, 2019 by Gerrit Coetzee 20 Comments

[BlueFlower] sends in this cool wine bottle engraver. It’s a simple machine that reminds us of the infamous EggBot. One axis can move in x and z while the other axis rotates the work piece. The EggBot works in spherical coordinates while this one lives in a cylindrical world.

The base of the device appears to be an older project of [BlueFlower]’s an XY-Plotter/Cutter. The plotter itself is a very standard twin-motor gantry design. In fact, it looks like when the machine is converted to bottle engraving, the drivers which previously moved the Y-axis are re-purposed to move two rollers. The rollers themselves are suspiciously similar to those found inside 2D printers. We all have them kicking around our junk drawers, but it’s rare to see them actually being used. The spindled is just a DC motor with a ball grinder coupled to the end.

As for the final result, we have to admit that the engraved bottles are quite fetching. Catch a video of the engraving process after the break.

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