Opening A Curta — With Great Care

August 12, 2023 by Chris Lott 29 Comments

We’ve always admired Curta mechanical calculators, and would be very hesitant to dismantle one. But [Janus Cycle] did just that — and succeeded. A friend sent him a Curta Model 2 calculator that was frozen up. Just opening the case involved percussive force to remove a retaining pin, and once inside he discovered the main shaft had been slightly bent. No doubt this calculator had suffered a drop at some point in the past.

I’m sticking to the rule of doing no harm — I’d rather not be able to fix this than do something that causes more problems.

But surprisingly, he was able to get it substantially back in working order without completely taking apart all 600+ parts. Most of the issues were shafts whose lubrication had become gummy, and one carry lever was slightly bent. There is still a little more work, but soon this calculator will once again be cranking out results.

Has anyone dismantled a mechanical contraption this complicated before, for example a teletype machine? Let us know in the comments. If you want to brush up on your Curta knowledge, check out the Curta Calculator Page. We also wrote a Retrotechtacular about the Curta before. Thanks to [mister35mm] for sending in this tip.

Continue reading “Opening A Curta — With Great Care” →

Inside Mechanical Calculators

May 1, 2018 by Dan Maloney 25 Comments

For as busy as things can get at the grocery store on a typical afternoon just before the dinner hour, at least the modern experience has one thing going for it: it’s relatively quiet. Aside from the mumbled greetings and “Paper or plastic?” questions from the cashier, and the occasional screaming baby in the next aisle, the only sound you tend to hear is the beeping of the barcode scanner as your purchase is tallied up.

Jump back just 40 years and the same scene was raucous, with cashiers reading price tags and pounding numbers into behemoth electromechanical cash registers. Back then, if you wanted help with any arithmetic with more than just a few operations, some kind of mechanical calculator was your only choice. From simple “one-banger” adding machines to complex analog computers, mechanical devices were surprisingly capable data processing tools. Here’s a brief look at how some of the simpler ones worked.

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3D Printed Curta Gets Upgrades

August 1, 2017 by Inderpreet Singh 16 Comments

It is amazing how makers can accomplish so much when they put their mind to something. [Marcus Wu] has uploaded a mesmerizing video on how to build a 3D printed Curta Mechanical Calculator. After nine iterations of design, [Marcus] presents a polished design that not only works but looks like a master piece.

For the uninitiated, the Curta is a mechanical calculator designed around the time of World War II. It is still often seen used in time-speed-distance (TSD) rallies to aid in the computation of times to checkpoints, distances off-course and so on. Many of these rallies don’t allow electronic calculators, so the Curta is perfect. The complex inner workings of the contraption were a key feature and point of interest among enthusiasts and the device itself is a highly popular collectible.

As for the 3D printed design, the attention to detail is impeccable. The current version has around 80 parts that need to 3D printed and a requires a few other screws and springs. Some parts like the reversing lever and selector knobs have been painted and digits added to complete the visual detail. The assembly took [Marcus Wu] around 40 minutes to complete and is one of the most satisfying builds we have ever seen.

What is even more amazing is that [Markus Wu], who is a software engineer by profession has shared all the files including the original design files free of cost on Thingiverse. A blog with written instructions is also available along with details of the iterations and original builds. We already did a post on a previous version so check it out for a little more background info.

Thanks for the tip [lonestar] Continue reading “3D Printed Curta Gets Upgrades” →

3D Printed Math Grenade

July 17, 2017 by Inderpreet Singh 23 Comments

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.

Retrotechtacular: The CURTA Mechanical Calculator

September 16, 2014 by Kristina Panos 39 Comments

The CURTA mechanical calculator literally saved its inventor’s life. [Curt Herzstark] had been working on the calculator in the 1930s until the Nazis forced him to focus on building other tools for the German army. He was taken by the Nazis in 1943 and ended up in Buchenwald concentration camp. There, he told the officers about his plans for the CURTA. They were impressed and interested enough to let him continue work on it so they could present it as a gift to the Führer.

This four-banger pepper mill can also perform square root calculation with some finessing. To add two numbers together, each must be entered on the digit setting sliders and sent to the result counter around the top by moving the crank clockwise for one full rotation. Subtraction is as easy as pulling out the crank until the red indicator appears. The CURTA performs subtraction using nine’s complement arithmetic. Multiplication and division are possible through successive additions and subtractions and use of the powers of ten carriage, which is the top knurled portion.

Operation of the CURTA is based on [Gottfried Leibniz]’s stepped cylinder design. A cylinder with cogs of increasing lengths drives a toothed gear up and down a shaft. [Herzstark]’s design interleaves a normal set of cogs for addition with a nine’s complement set. When the crank is pulled out to reveal the red subtraction indicator, the drum is switching between the two sets.

Several helper mechanisms are in place to enhance the interface. The user is prevented from ever turning the crank counter-clockwise. The crank mechanism provides tactile feedback at the end of each full rotation. There is also a lock that disallows switching between addition and subtraction while turning the crank—switching is only possible with the crank in the home position. There is a turns counter on the top which can be set to increment or decrement.

You may recall seeing Hackaday alum [Jeremy Cook]’s 2012 post about the CURTA which we linked to. A great deal of information about the CURTA and a couple of different simulators are available at curta.org. Make the jump to see an in-depth demonstration of the inner workings of a CURTA Type I using the YACS CURTA simulator.

Continue reading “Retrotechtacular: The CURTA Mechanical Calculator” →

Hackaday Links May 9th 2012

May 9, 2012 by Jeremy Cook 18 Comments

Homecut – CNC Cutting Directory

So you have a CNC machine that you use as a hobby, but would like to do some actual work on the side? Or maybe you have an idea you’d like made. Homecut is a map directory where you can maybe hook up with the right person.

The Curta Mechanical Calculator

As [leehart] mentioned in our comments section, the Curta mechanical calculator is a truly ingenious piece of engineering. A quick Google search should find all kinds of information on it, but this article could be a good place to start for some mechanical hacking inspiration!

Luxman Amplifier DAC Upgrade

[R. Barrios] wasn’t happy with using the sound card for his HTPC setup, so decided to add a DAC module onto his reciever. The resulting audio quality was very good, and the build came out quite clean. Check it out if you’re thinking of a hack-upgrade to your stereo equipment.

3D Printable Tilt-Shift Adapter

A tilt-shift lens a neat piece of equipment that is used to make a large scene look like they were miniatures. It’s a cool effect, but professional lenses to do this can cost thousands of dollars. This Instructable tells you how to go about printing your own. For more info on the technique itself, check out this Wikipedia article.

New 3D Printer on the Block

If you would like to take the plunge into 3D printing, but are looking for somewhere to get a parts kit, the [ORD Bot Hadron 3D Printer] may be worth a look. The build quality looks great, and the price for the mechanical components is quite reasonable at $399. You’ll need to provide the electronics and extruder. Thanks [comptechgeek]!