3D printed Math Grenade

Calculator hacks are fun and educational and an awesome way to show-off how 1337 your skills are. [Marcus Wu] is a maker who likes 3D printing and his Jumbo Curta Mechanical Calculator is a project from a different era. For those who are unfamiliar with the Curta, it is a mechanical calculator that was the brainchild of Curt Herzstark of Austria from the 1930s. The most interesting things about the design were the compactness and the complexity which baffled its first owners.

The contraption has setting sliders for input digits on the side of the main cylindrical body. A crank at the top of the device allows for operations such as addition and subtraction with multiplication and division requiring a series of additional carriage shift operations. The result appears at the top of the device after each crank rotation that performs the desired mathematical operation. And though all this may seem cumbersome, the original device fit comfortably in one hand which consequently gave it the nick name ‘Math Grenade’.

[Marcus Wu] has shared all the 3D printable parts on Thingiverse for you to make your own and you should really take a look at the video below for a quick demo of the final device. There is also a detailed set of images (82 or so) here that present all the parts to be printed. This project will test your patience but the result is sure to impress your friends. For those looking to dip your toes in big printed machines, check out these Big Slew Bearings for some inspiration.

24 thoughts on “3D printed Math Grenade

  1. I wish someone would make replicas, like real ones the same as the original. I want one, they are intriguing, but I’m not a collector and don’t put that kind of value on them.

      1. ++1
        I always wanted a Curta. Have an addiator, but something is a bit cooler about a tubular thing that you have to crank to get your numbers out. +1 if you also can put a hunk of parmesan in it and use it as a tabletop cheese grater.

    1. I kinda agree with you. I actually do collect calculators. I have an old 1930’s Burroughs manual in perfect working order, and I had a Friden STW-10 that needed repair, I recently got a second STW-10 for next to nothing, and hope to get at least one of them working. I even have a wide variety of calculators form the electronic era! I have a SCM Cogito 240SR, a Friden EC-132, a Commodore 512, a Wang 360SE, A Sony Sobax ICC-600W and many, many others! One thing that NEVER came to mind when thinking of these early calculators, is “small”. ALL these old machines are gargantuan BEASTS! XD

      And then there’s the Curta… The “Peppergrinder”, the “Math Grenade”… Truth is, the prices I see them sell for are probably fair, but dang it, It’s still too rich for my blood! I’d be 100% cool with a repro that could be had for a song, compared to the rather expensive collectible. I kinda wonder where the rights sit? Are the patents expired by this now? Does some company still hold some limited or full right to the name or trademarks? Hmm…

      I’d definitely buy a “repro” Curta, if it were significantly cheaper than the real deal. Collector’s premium is a cruel, cruel beast… I collect for the desire to have these engineering marvels, not necessarily for the desire to have a genuine piece of history (though it’s a nice bonus). An example, is I certainly have never been able to afford a Bell Punch Anita calculator (with “thyratron” cold cathode gas tube based decade counters), like the Anita Mk. 7 through Mk. 10. In 2010, I had the opportunity come up to get six of the thyratron decade counter boards from an Mk. 7, even though the rest of the machine was long gone. I bought them gladly. I currently have 6 bare boards, each with 10 neon tubes and a nixie tube. They do absolutely nothing at the moment, but before I croak, i’d like to build a power supply to power them, and construct a simple enclosure to show them off. I’ll use rotary dials from old school rotary telephones to generate the counting pulses (as opposed to the original Anita’s full entry keyboard). Each board has a carry output that goes tot he next board, and each board contains all the hardware to maintain it’s count and display it’s digit.

      Will it be a real Anita? No… It’ll be a homebrew built with some Anita parts, but I’m TOTALLY cool with that, for the time being.

      Likewise, I’d be cool with a 3D printed Curta, or a repro Curta with a “Made in China” sticker.

    2. I’m surprised Curta-Clones haven’t been manufactured by the industrious Chinese manufacturers yet. The price on the open market for a quality Curta-Clone would probably top $100 USD or more for one. The originals are available for copying so that’s not an obstacle. The Chinese certainly have the precision automated tooling and know-how that is required (not to mention the ability to scale production). Maybe some-day… Or maybe it’s that Roman Numerals don’t have any up-take in China for a device like this? Nah, the clones would be targeting the Western markets, right?

  2. Amazing, to get something with that many parts and critical dimensions to work so well is a very impressive achievement. The real thing is very collectable, you’d be lucky to find a working unit for less than $1000.

    1. Anyone lucky enough to buy a working one – don’t take it apart. In previous articles the majority of them returned for repair were actually returned because the curious owners could not figure out how to reassemble it.

      It is one of my greatest regrets – they were still available new into the 1970s, but electronic calculators were more attractive.

    2. I think it was more a matter of time spent than his design chops, Which are pretty impressive given the mechanical complexity of the mechanism.

      “To combat this problem, I designed the various parts to fit too tightly. After some filing / sanding,
      they fit perfectly and lack high areas that wear away quickly. Unfortunately, this also means that
      each part has to be filed and tested against its mating parts for fit repeatedly until the desired fit
      is achieved. It is tedious and time-consuming, but necessary for reliable function.”

    1. A while back I looked into getting one, and found several on ebay for about $400. Now I’m kicking myself for not getting two. Assuming they weren’t scams (why would you scam with something that specific?*)

      * I realize the asking of this question is probably its own answer

    2. Actually that’s a fair amount of depreciation. Woulda cost 14000 dollars by today’s uber-inflationary period.
      Now a 58 mustang… there’s something that has held its value :)

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