Screwy Math For Super Fine Adjustments: Differential Screws

March 21, 2020 by Danie Conradie 38 Comments

For any sort of precision machine, precision adjustability is required. For the hacker this usually involves an adjustment screw, where the accuracy is determined by the thread pitch. This was not good enough for [Mark Rehorst] who wanted adjustment down to 10 μm for his 3D printer’s optical end-stop, so he made himself a differential adjustment screw.

Tiny adjustment can be made to the green block due to the thread pitch differences

Differential screws work by having two threads with a slightly different pitch on the same shaft. A nut on each section of thread is prevented from rotating in relation to the other, and when the screw is turned their relative position will change only as much as the difference between the two thread pitches.

The differential screw in this case started life as a normal M5 bolt with a 0.8 mm thread pitch. [Mark] machined and threaded section of the bolt down to a M4 x 0.7 mm thread. This means he can get 0.1 mm (100 μm) of adjustment per full rotation. By turning the bolt 1/10 rotation, the relative movement comes down to 10 μm.

This mechanism is not new, originating from at least 1817. If you need fine adjustments on a budget, it’s a very elegant way to achieve it and you don’t even need a lathe to make your own. You can partially drill and tap a coupling nut, or make a 3D printed adapter to connect two bolts.

Fabricating precision tools on a budget is challenging but not impossible. We’ve seen some interesting graphite air bearings, as well as a 3D printed microscope with a precision adjustable stage.

Motorizing A Plasma Cutter On The Cheap

December 23, 2019 by Tom Nardi 5 Comments

A hand-held plasma cutter is an excellent tool to have if you are working with sheet metal, but it’s not particularly well suited to making long or repetitive cuts. Which is why [workshop from scratch] worked his usual scrapheap magic and built his own motorized track for making perfectly straight cuts.

Most of the frame, and even the small truck that rides on it, is made out of square stock in various sizes. A couple of bearings are enough to make sure the movement is smooth and doesn’t have too much slop. Motion is provided by a long threaded rod and two nuts, which are welded to the side of the truck.

If you had the patience (and forearm strength) you could just put a crank on the rod and be done with it, but in this case [workshop from scratch] used the motor, gearbox, and chuck from an old electric drill to grab onto the threaded rod and do the spinning for him. He rigged up an enclosure for the side of the rack that holds the motor, DC power supply, and motor controller, along with a couple of switches and a knob to control the speed.

A modification allows him to enable the plasma cutter with one of the switches on the panel, which gives the setup a much more complete feel than just putting a zip tie on the trigger. With this design, the plasma cutter itself can still be removed from the mount and used normally. You can even remove the motorized component with a few bolts if you just wanted to do manual cuts on the bed.

In the video after the break, the keen-eyed viewer may notice a few familiar pieces of gear in the background, such as the hydraulic bench vise we covered earlier in the year. As the name of the channel implies, [workshop from scratch] is all about building the workshop tools that many take for granted, and they’ve all been phenomenally fascinating projects. While we admire the gumption it takes to try and build a lathe out of scrap granite slabs, there’s something to be said for DIY tools that end up looking nearly as good as commercial offerings.

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Scratch Building A Lathe From Pieces Of Granite

October 29, 2019 by Tom Nardi 12 Comments

As hackers, we’re well accustomed to working with what we have on hand. That’s the name of the game, really. A large majority of the projects that have graced these pages are the direct result of trying to coerce a piece of hardware or software into doing something it was never designed to do, for better or for worse.

But even still, attempting to build a functional lathe using scrap pieces from granite countertops is a new one for us. [Nonsense Creativity] has spent the last several months working on this build, and as of his latest video, it’s finally getting to the point at which the casual observer might recognise where he’s going with it.

We won’t even hazard a guess as to the suitability of thick pieces of granite for building tools, but we’re willing to bet that it will be plenty heavy enough. Then again, his choice of building material might not be completely without precedent. After all, we once saw a lathe built out of concrete.

Building a lathe out of what you’ve got laying around the shop is of course something of a tradition at this point., but if you’re not quite up to the challenge of cutting your own metal (or granite, as the case may be), [Quinn Dunki] has put together a lathe buying guide that you may find useful.

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How Art Became Science In Machining

May 7, 2019 by Quinn Dunki 57 Comments

Machining is one of those fascinating fields that bridges the pre-scientific and scientific eras. As such, it has gone from a discipline full of home-spun acquired wisdom and crusty old superstitions to one of rigorously analyzed physics and crusty old superstitions.

The earliest machinists figured out most of what you need to know just by jamming a tool bit into spinning stock and seeing what happens. Change a few things, and see what happens next. There is a kind of informal experimentation taking place here. People are gradually controlling for variables and getting better at the craft as they learn what seems to affect what. However, the difference between fumbling around and actually knowing something is controlling for one’s own biases in a reproducible and falsifiable way. It’s the only way to know for sure what is true, and we call this “science”. It also means being willing to let go of ideas you had because the double-blinded evidence clearly says they are wrong.

That last part is where human nature lets us down the most. We really want to believe things that confirm our preconceived notions about the world, justify our emotions, or make us feel better. The funny thing about science, though, is that it doesn’t care whether you believe in it or not. So go get your kids vaccinated, and up your machining game with scientific precision. Let’s take a look.

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Hack Chat: The Home Machine Shop With Quinn Dunki

March 18, 2019 by Dan Maloney 4 Comments

Join us Wednesday at noon Pacific time for the Home Machine Shop Hack Chat!

Even if you haven’t been here for very long, you’ll probably recognize Quinn Dunki as Hackaday’s resident consulting machinist. Quinn recently did a great series of articles on the “King of Machine Tools”, the lathe, covering everything from the history of precision machine tools to making your first chips. She’s documented the entire process of procuring and setting up a new lathe, pointing out all the potential pitfalls the budding home machinist may face. You can get a much deeper dive into her machining adventures on her YouTube channel, Blondihacks.

Flinging hot metal chips around is hardly all Quinn has accomplished, though. Long before her foray into machine tools, there was Veronica, a scratch-built 6502 machine Quinn created as an homage to the machines that launched her into a life of writing software. We’ve featured Veronica on our pages a couple of times, and she’s always made quite a hit.

Please join us for this Hack Chat, where we’ll discuss:

How developing software and machining are alike, and how they differ;
How social networks have changed the perception of machining;
Best practices for getting started in machining; and
Are there any new machine tool purchases in the pipeline?

You are, of course, encouraged to add your own questions to the discussion. You can do that by leaving a comment on the Home Machine Shop Hack Chat and we’ll put that in the queue for the Hack Chat discussion.

Our Hack Chats are live community events on the Hackaday.io Hack Chat group messaging. This week we’ll be sitting down on Wednesday, March 20, at noon, Pacific time. If time zones have got you down, we have a handy time zone converter.

Click that speech bubble to the right, and you’ll be taken directly to the Hack Chat group on Hackaday.io. You don’t have to wait until Wednesday; join whenever you want and you can see what the community is talking about.

Already Impressive CNC Router Gets An Extra Axis

November 25, 2018 by Dan Maloney 6 Comments

The type of CNC machine within the financial reach of most DIYers is generally a three-axis affair, with a modest work envelope and a spindle that never quite seems powerful enough. That’s not to say that we don’t covet such a machine for our own shop of course, but comparing small machines with the “big boy” five-axis tools might leave the home-gamer feeling a tad inadequate.

Luckily, there’s a fix that won’t necessarily break the bank: adding a fourth axis to your CNC router. [This Old Tony] tore into his CNC router – a build we’ve featured before and greatly admire – to add a machine spindle that lets him work with the machine much as if it was a CNC lathe. The first video below covers the mechanical part of the build, which involves welding and machining a sturdy assembly to hold a spindle connecting a four-jaw chuck to a Lexium MDrive, a stepper motor with integrated driver and feedback that makes it act more like a servo. [Old Tony] covered integrating the drive into Mach4 in a previous video.

The assembled machine spindle is a beefy looking affair that can smoothly ramp up to 3000 rpm and has decent enough holding torque to allow it to act as an indexing head in addition to a lathe. The second video below shows some tests turning aluminum and steel; we were surprised by how aggressive the cuts can be before stalling the spindle.

No, it’s not a Tormach or Haas or even a Pocket NC, but it’s a great addition to an already capable machine, and we’re looking forward to what [Old Tony] cranks out with it.

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Lathe Headstock Alignment: Cutting A Test Bar

August 7, 2018 by Quinn Dunki 39 Comments

Let’s say you’ve recently bought a lathe and set it up in your shop. Maybe you’ve even gone and leveled it like a boss. You’re ready to make chips, right? Well, not so fast. As real machinists will tell you, you can use all the levels and lasers and whatever that you want, but the proof is in the cut. Precision leveling gets your machine in the ballpark (machinists have very small ballparks) but the final step to getting a machine to truly perform well is to cut a test bar. This is a surefire way to eliminate any last traces of twist in the bed.

There are two types of test bars. One is for checking headstock-to-ways alignment, which is what we’re doing here. There’s another type used for checking tailstock alignment, but that’s a subject for another day.

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