[Ben Krasnow]’s Take On DIY Air Bearings

We’ve got to admit that watching [Ben Krasnow]’s new video on air bearings is tough. We found our eyes constantly checking the spherical air bearing in the foreground, which for the first eight minutes of the video just kept going. It was strangely hypnotic, and made it hard to concentrate on all the other cool stuff [Ben] was up to.

If the topic of air bearings seems familiar, it might be because we recently reported on DIY air bearings made from used EDM electrodes. [Ben] saw that too, and dusted off his old air bearing project. Literally, as it turns out, because the graphite blocks whose porosity and softness make them the perfect material for air bearings also makes for a dusty workshop. We’d recommend breathing protection of some sort while machining graphite. In addition to simple puck bearings, [Ben] came up with more complicated designs, including the aforementioned spherical bearing. He used the steel ball itself as a precision tool to grind the graphite out, first by coating it with abrasive and then by cutting grooves in it to act like a file. A cylindrical bearing was also cut, this time with sandpaper glued directly to the ground steel rod that would seat in the bearing.

[Ben]’s other innovation is vacuum preloading, where he applies both vacuum and pressure to the bearing plenum. The vacuum provides the force needed to capture the moving element while the pressure bears the load. It’s a careful balancing act, but it works well enough to capture the large steel ball and keep it turning effortlessly.

We really liked [Ben]’s take on air bearings, especially his thoughts on creating fully enclosed cylindrical bearings. Those could be useful for low-friction linear drives, and we look forward to seeing more on those.

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Used EDM Electrodes Repurposed As Air Bearings For Precision Machine Tools

If you’ve ever played air hockey, you know how the tiny jets of air shooting up from the pinholes in the playing surface reduce friction with the puck. But what if you turned that upside down? What if the puck had holes that shot the air downward? We’re not sure how the gameplay would be on such an inverse air hockey table, but [Dave Preiss] has made DIY air bearings from such a setup, and they’re pretty impressive.

Air bearings are often found in ultra-precision machine tools where nanometer-scale positioning is needed. Such gear is often breathtakingly expensive, but [Dave]’s version of the bearings used in these machines are surprisingly cheap. The working surfaces are made from slugs of porous graphite, originally used as electrodes for electrical discharge machining (EDM). The material is easily flattened with abrasives against a reference granite plate, after which it’s pressed into a 3D-printed plastic plenum. The plenum accepts a fitting for compressed air, which wends its way out the micron-sized pores in the graphite and supports the load on a thin cushion of air. In addition to puck-style planar bearings, [Dave] tried his hand at a rotary bearing, arguably more useful to precision machine tool builds. That proved to be a bit more challenging, but the video below shows that he was able to get it working pretty well.

We really enjoyed learning about air bearings from [Dave]’s experiments, and we look forward to seeing them put to use. Perhaps it will be in something like the micron-precision lathe we featured recently.

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The Machinists’ Mantra: Precision, Thy Name Is Rigidity

“Everything is a spring”. You’ve probably heard that expression before. How deep do you think your appreciation of that particular turn of phrase really is? You know who truly, viscerally groks this? Machinists.

As I’ve blathered on about at length previously, machine tools are all about precision. That’s easy to say, but where does precision really come from? In a word, rigidity. Machine tools do a seemingly magical thing. They remove quantities of steel (or other materials medieval humans would have killed for) with a slightly tougher piece of steel. The way they manage to do this is by applying the cutting tool to the material within a setup that is so rigid that the material has no choice but to yield. Furthermore, this cutting action is extremely precise because the tool moves as little as possible while doing so. It all comes down to rigidity. Let’s look at a basic turning setup.

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Precision Pantograph Probes PCBs

Electronic components are getting smaller and for most of us, our eyesight is getting worse. When [Kurt] started using a microscope to get a better view of his work, he realized he needed another tool to give his hands the same kind of precision. That tool didn’t exist so he built it.

The PantoProbe is a pantograph mechanism meant to guide a probe for reaching the tiny pads of his SMT components. He reports that he has no longer has any trouble differentiating pins 0.5 mm apart which is the diameter of the graphite sticks in our favorite mechanical pencils.

[Kurt] has already expanded his machine’s capability to include a holder for a high-frequency probe and even pulleys for a pick-and-place variation. There’s no mention of dual-wielding PantoProbes as micro-helping-hands but the versatility we’ve seen suggests that it is only a matter of time.

Four bar linkages are capable of some incredible feats and they’re found all around us. Enjoy one of [Kurt]’s other custom PCBs in his Plexitube Owl Clock, or let him show you to make 3D objects with a laser engraver.

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Hackaday Trims Its Own Resistors

There are times when you might want an odd-value resistor. Rather than run out to the store to buy a 3,140 Ω resistor, you can get there with a good ohmmeter and a willingness to solder things in series and parallel. But when you want a precise resistor value, and you want many of them, Frankensteining many resistors together over and over is a poor solution.

Something like an 8-bit R-2R resistor-ladder DAC, for instance, requires seventeen resistors of two values in better than 0.4% precision. That’s just not something I have on hand, and the series/parallel approach will get tiresome fast.

Ages ago, I had read about trimming resistors by hand, but had assumed that it was the domain of the madman. On the other hand, this is Hackaday; I had some time and a file. Could I trim and match resistors to within half a percent? Read on to find out.

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Moving Microns With A High Precision Linear Stage

As anyone who has experimented with their own home-made CNC machinery will tell you, precision isn’t cheap. You can assemble a gantry mill using off-the-shelf threading and kitchen drawer slides. But it’s a safe assumption that if you put the tool at a particular position it won’t be quite at the same position next time you return. But if you take your budget from dirt cheap to reasonably priced you can do much better. [Adam Bender] designs high-precision automation systems for a living, so when he needed a precision linear stage for a personal project he achieved micron level accuracy for under $500.

micron-precision-linear-actuator
Red parts are the two spring-loaded nuts

He explains the problem of backlash with an inexpensive lead screw — the wiggle between threaded components that cause positional chaos. His solution uses two nuts preloaded against each other with a spring. There is still a stick-slip issue; a tendency to move in lurches due to differences between the coefficients of static and dynamic friction between the materials. Careful choice of machining stock for the nut to picking materials in which these coefficients were almost identical reduced the stick-slip to as little as possible.

He goes into significant detail on the design, manufacture, and testing of all the components of his stage, its body, sealing system, and control. If you are a precision CNC guru maybe you’ll find it interesting as a cleverly designed component, but if you are a mere dilettante you’ll find it fascinating to read a comprehensive but accessible write-up from a professional in the field.

This build probably goes a step beyond most we’ve featured in the past, but that’s not to say we’ve not seen some pretty good efforts.

Shop Made Squareness Comparator

[Stefan Gotteswinter] has a thing for precision. So it was no surprise when he confessed frustration that he was unable to check the squareness of the things he made in his shop to the degree his heart desired.

He was looking enviously at the squareness comparator that [Tom Lipton] had made when somone on Instagram posted a photo of the comparator they use every day. [Stefan] loved the design and set out to build one of his own. He copied it shamelessly, made a set of drawings, and got to work.

[Stefan]’s videos are always a trove of good machine shop habits and skills. He always shows how being careful, patient, and doing things the right way can result in really astoundingly precise work out of a home machine shop. The workmanship is beautiful and his knack for machining is apparent throughout. We chuckled at one section where he informed the viewer that you could break a tap on the mill when tapping under power if you bottom out. To avoid this he stopped at a distance he felt was safe: 0.5 mm away.

The construction and finishing complete, [Stefan] shows how to use the comparator at the end of the video, viewable after the break.

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