Improving Cheap Ball Screws

Most 3D printers use leadscrews for at least one axis. These are simple devices that are essentially a steel screw thread and a brass nut that travels on it. However, for maximum precision, you’d like to use a ball screw. These are usually very expensive but have many advantages over a leadscrew. [MirageC] found cheaper ball screws but, since they were inexpensive, they had certain limitations. He designed a simple device that improves the performance of these cheap ball screws.

Superficially, a ball screw looks like a leadscrew with an odd-looking thread. However, the nut is very different. Inside the nut are ball bearings that fit in the grooves and allows the nut to spin around with much less friction. A special path collects the ball bearings and recirculates them to the other side of the nut. In general, ball screws are very durable, can handle higher loads and higher speeds, and require less maintenance. Unlike leadscrews, they are more expensive and are usually quite rigid. They are also a bit noisier, though.

Ball screws are rated C0 to C10 precision where C10 is the least accurate and the price goes up — way up — with accuracy. [MirageC] shows how cheaper ball screws can be rolled instead of precision ground. These screws are cheaper and harder, but exhibit more runout than a precision screw.

This runout caused wobble during 3D printing that was immediately obvious on the prints. Using a machinist’s dial gauge, [MirageC] found the screws were not straight at all and that even a relatively poor C7 ball screw would be more precise.

The solution? A clever arrangement of 3D printed parts. ball bearings, and magnets. The device allows the nut to move laterally without transmitting it to the print bed. It is a clever design and seems to work well.

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Vertical Mill Completes Scrapyard Lathe Build

One thing’s for sure: after seeing [Roland Van Roy] build a vertical mill from industrial scrap, we’ve got to find a better quality industrial scrapyard to hang around.

The story of this build started, as many good shop stories do, at the lathe, which in this case was also a scrapyard build that we somehow managed to miss when it first posted. This lathe is decidedly different from the common “Gingery method” we’ve seen a few times, which relies on aluminum castings. Instead, [Roland] built his machine from plate stock, linear slides, and various cast-off bits of industrial machines.

To make his lathe yet more useful, [Roland] undertook this build, which consists of a gantry mounted over the bed of the lathe. The carriage translates left and right along the bed while the spindle, whose axis lines up perfectly with the center axis of the lathe, moves up and down. [Roland] added a platform and a clever vise to the lathe carriage; the lathe tool post and the tailstock are removed to make room for these mods, but can be added back quickly when needed. Digital calipers stand in for digital read-outs (DROs), with custom software running on a Picaxe and a homebrew controller taking care of spindle speed control.

[Roland] reports that the machine, weighing in at about 100 kg, exhibits a fair amount of vibration, which limits him to lighter cuts and softer materials. But it’s still an impressive build, and what really grabbed us was the wealth of tips and tricks we picked up. [Roland] used a ton of interesting methods to make sure everything stayed neat and square, such as the special jig he built for drilling holes in the T-slot extrusions to the use of cyanoacrylate glue for temporary fixturing.

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Over-Engineered Bottle Opener Takes The Drudgery Out Of Drinking

Some projects take but a single glance for you to know what inspired them in the first place. For this over-engineered robotic bottle opener, the obvious influence was a combination of abundant free time and beer. Plenty of beer.

Of course there are many ways to pop the top on a tall cold one, depending on the occasion. [Matt McCoy] and his cohorts selected the “high-impulse” method, which when not performed by a robot is often accomplished by resting the edge of the cap on a countertop and slapping the bottle down with the palm of one’s hand. This magnificently pointless machine does the same thing, except with style.

The bottle is placed in a cradle which grips it, gently but firmly, and presents it to the opening mechanism in a wholly unnecessary motion-control ballet. Once in place, a lead screw moves a carriage down, simultaneously storing potential energy in a bundle of elastic surgical tubing while tripping a pawl on the edge of the cap. A lever trips at the bottom of the carriage’s travel, sending the pawl flying upward to liberate the libation, giving the robot a well-deserved and sudsy showers. Behold the wonderful interplay of 190 custom parts — and beer — in the video below.

Hats off to [Matt] et al for their tireless efforts on behalf of beleaguered beer-openers everywhere. This seems like the perfect accessory to go along with a game of mind-controlled beer pong.

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Gorgeous Mini-Lathe Makes The Most Out Of Wood And Metal

It’s a cliche that the only machine tool that can make copies of itself is the lathe. It’s not exactly true, but it’s a useful adage in that it points out that the ability to make big round things into smaller round things, and to make unround things into round things, is a critical process in so many precision operations. That said, making a lathe primarily out of wood presents some unique challenges in the precision department

This isn’t [Uri Tuchman]’s first foray into lathe-building. Readers may recall the quirky creator’s hybrid treadle-powered and electric lathe, also primarily an exercise in woodworking. That lathe has seen plenty of use in [Uri]’s projects, turning both wood and metal stock into parts for his builds. It wasn’t really optimal for traditional metal turning, though, so Mini-Lathe 2 was undertaken. While the bed, headstock, and tailstock “castings” are wood — gorgeously hand-detailed and finished, of course — the important bits, like the linear slides for the carriage and the bearings in the headstock, are all metal. There’s a cross-slide, a quick-change tool post, and a manual lead screw for the carriage. We love the finely detailed brass handcranks, which were made on the old lathe, and all of the lovely details [Uri] always builds into his projects.

Sadly, at the end of the video below we see that the lathe suffers from a fair amount of chatter when turning brass. That’s probably not unexpected — there’s not much substitute for sheer mass whenit comes to dampening vibration. We expect that [Uri] will be making improvements to the lathe in the coming months — he’s not exactly one to leave a job unfinished.

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Mechanisms: Lead Screws And Ball Screws

Translating rotary motion to linear motion is a basic part of mechatronic design. Take a look at the nearest 3D-printer or CNC router — at least the Cartesian variety — and you’ll see some mechanism that converts the rotation of the the motor shafts into the smooth linear motion needed for each axis.

Hobby-grade machines are as likely as not to use pulleys and timing belts to achieve this translation, and that generally meets the needs of the machine. But in some machines, the stretchiness of a belt won’t cut it, and the designer may turn to some variety of screw drive to do the job.

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Mechanisms: The Screw Thread

They hold together everything from the most delicate watch to the largest bridge. The world is literally kept from coming apart by screws and bolts, and yet we don’t often give a thought to these mechanisms. Part of that is probably because we’ve gotten so good at making them that they’re seen as cheap commodities, but the physics and engineering behind the screw thread is interesting stuff.

We all likely remember an early science lesson wherein the basic building blocks of all mechanisms laid out. The simple machines are mechanisms that use an applied force to do work, such as the inclined plane, the lever, and the pulley. For instance, an inclined plane, in the form of a splitting wedge, directs the force of blows against its flat face into a chunk of wood, forcing the wood apart.

Screw threads are another simple machine, and can be thought of as a long, gently sloped inclined plane wrapped around a cylinder. Cut a long right triangle out of paper, wrap it around a pencil starting at the big end, and the hypotenuse forms a helical ramp that looks just like a thread. Of course, for a screw thread to do any work, it has to project out more than the thickness of a piece of paper, and the shape of the projection determines the mechanical properties of the screw.

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Huge 3D Printer Ditches Lead Screw For Belt Driven Z Axis

The vast majority of desktop 3D printers in use today use one or more lead screws for the Z-axis. Sometimes you need to think outside of the box to make an improvement on something. Sometimes you need to go against the grain and do something that others wouldn’t do before you can see what good will come out of it. [Mark Rehorst] had heard the arguments against using a belt drive for the Z-axis on a 3D printer build:

  1. The belt can stretch, causing inaccurate layer height.
  2. If power fails, gravity will totally ruin your day.

He decided to go for it anyway and made a belt driven Z axis for his huge printer. To deal with the power loss issue, he’s using a 30:1 reduction worm gear on the drive — keeping the bed in one place if power goes. And after a few studies, he found the belt stretch was so minimal that it has no effect on layer height.

Of course those two issues are but a small portion of the overall ingenuity that [Mark] poured into this project. You’ll want to see it in action below, printing a vase that is 500 mm tall (took about 32 hours to get to 466 mm and you can see the top is a hairy wobbly at this point). Luckily we can geek out with the rest of his design considerations and test by walking through this fantastic build log from back in July. Of note is the clamp he designed to hold the belt. It uses a small scrap of the belt itself to lock together the two ends. That’s a neat trick!

The introduction of a belt driven Z-axis eliminates Z-axis wobble — an issue that can be exacerbated in tall printers. Desktop 3D printers are constantly improving, and we’re always excited to see a new trick work so well. Let us know if you’ve seen any other handy Z-axis modifications out there.

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