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Curta Calculator Type I scaled at 3:1

by mwu, published

Curta Calculator Type I scaled at 3:1 by mwu Dec 6, 2016
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Summary

The Amazing Curta Calculator is now 3D Printable!

I am doing an Ask me anything on Reddit /r/3Dprinting on Tuesday Sept 19th at 3pm EST / 12pm PST!

New group for discussion, bragging rights, and help with Curta builds: https://www.thingiverse.com/groups/curta

Bill of Materials
Build Manual
Assembly Video (The build manual contains more details, but this is a good visual guide)
See video of the Curta in action.
See for my original build for details on the project.
The CAD files are shared on OnShape

Update 10/20/2017
Updated the BOM to fix the size of the upper carriage spring and eliminate confusion in description of the main body.

Update 9/29/2017
Updated the BOM to add a file name column to make it easier to find the correct files. Also removed the remaining references to the old 0.25mm nozzle requirement.

Update 9/11/2017
Added a split step drum to reduce the required printer print volume! Minimum print volume is now 160x160x170mm!

Update 8/21/2017
Fixed some naming problems with files and in the BOM. Also added the two files I had missed below into the BOM.

Update 8/18/2017
Added missing bolt sleeves for zero positioning lever and anti reversal pawl.

Update 7/6/2017
After manually aligning all the 5mm number stencils on the lower and upper housing and then messing up the paint, I decided to create stencils for it (lower_housing.dxf and upper housing numbers.dxf). Those stencils are now uploaded.

Also, I have added a group for those building the Curta. I will be answering questions there and I look forward to seeing pictures of people's in-progress builds: https://www.thingiverse.com/groups/curta

Update 6/27/2017
Updated the main axle and step drum model. The old one works, but the hole for the crank handle pin was 90 degrees off. This change is basically cosmetic.

Update 5/3/2017

  • Updated a few files that were requiring too much manual fitting work.
  • The zero positioning disk is updated for easier printing / better teeth for the anti-reversal pawl.
  • Added missing crank pin file.
  • Adding dxf files representing paint masks for numbering and lettering. I cut these from vinyl with a Cricut machine.
  • Updating the BOM because the torsion springs for anti-reversal pawl and zero positioning lever recommended in the BOM were way too strong. I ended up making these springs by hand. The BOM is now available as PDF and XLS files.
  • Adding the initial draft of the build manual. This covers the entire build process -- including making the springs mentioned above. Feedback on this build manual is desired and welcome -- help me improve it for others please.

Update 3/29/2017 -- In the process of preparing the build manual, I have a list of several files which need correcting to get correct assembly and functionality out of the Curta. I recommend waiting until I can get these changes published before doing much printing if you haven't yet. Particularly, the mount hole for the crank handle on the main shaft was 90 degrees from where it should have been.

While the build manual is taking me some time, I am excited by the progress on it so far. In the process I have disassembled and reassembled the second Curta which helped me find and eliminate extra friction. I will have another video of the Curta going up soon which will cover a simple, but difficult calculation that has eluded a correct result on the 3D printed Curta until now. That calculation is simply starting at 0, adding 1, then subtracting 1. The result should be a completely zero result with zero showing on the turns counter as well. Since the Curta utilizes addition for subtraction, the calculation requires the Curta to rotate every result and turns counter dial to 9 and a carry operation to cascade all the way around bringing each digit back to 0.

Update 3/9/2017 -- I have assembled a second Curta and taken loads of pictures along the way. I can now either work on a build manual utilizing the photos I took or a series of build videos. There are a LOT of photos and a lot of steps involved. What would you prefer (google form poll)?

Update 1/18/2017 -- I have updated the transmission gear and lockout parts to be printable using a 0.4mm nozzle instead of a 0.25mm nozzle. Thanks to the feedback from MikeHenry. I also updated a repaired Lower Housing.stl due to non-manifold edges.

Update 01/06/2017 -- I found that the tens bell also had non-manifold edges causing problems when slicing. A repaired copy has been uploaded.

Update 12/30/2016 -- I found that the main axle and step drum had non-manifold edges that may cause problems when slicing (Simplify3D skips a few layers in the next to last row of teeth). I uploaded a repaired copy.

Update 12/17/2016 -- I found a part I had missed uploading a file for. It's the securing spring for the zero positioning plate. I have now added the file and added it to the BOM.

Update 12/12/2016 -- I just added layer height, infill, orientation, and support notes to the printed files in the BOM. First step in getting actual build instructions.

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Important
I had a mistake in my BOM. The size of the upper carriage spring was listed as 1.8x28x25. That was incorrect. I have uploaded a fixed copy to the proper size -- 1.8x28x40. I didn't realize it until I ordered more at the wrong size. I hope this post prevents some of you from ordering incorrectly as the only source I know is in China and shipping takes a while.

I have a printer with a small build plate (area). I know that part of the coolness in this project is its size, but how small can I make the overall build before it's too small to print?

The scale is already about as small as it can be done on an FDM printer. It might be able to be scaled down a little bit if you use a small nozzle (such as the experimental high resolution 0.15 nozzle from e3d). I haven't tried it so I don't know if that would work. It would be very hard to get some of the parts to stick at that size and it would also involve scaling the parts down while keeping the tolerances the same (not scaled down).

Scaling it down means going back to the source CAD files and doing the work there rather than just scaling down these files in your slicer.

I'm not sure what kind of printer you have, but there have been a few posts from folks here who may be attempting a 2:1 scale Curta on an SLA printer.

can u sell me the dxf file all done on the vinyl pls

I'm working on a different way of doing the letters and numbers that won't require the vinyl. The vinyl isn't something I can easily reproduce and sell because the shapes are really too small for the machine. It tries to cut them, but fails on the small bits -- especially with numbers like 0 with an inside and an outside. I had to cut multiple copies for each set of numbers and combine the bits and pieces together. The vinyl also gets pulled and torn in places so it doesn't sit flat after cutting and won't ship very well.

bearing plate and zero positioning disc can u split in half so don't have to use up lots of support

can u sell me the dxf file all done on the vinyl pls
i have some pic of what i printed so far
Thank you

I am working on an easier system for getting the letters and numbers on the Curta. I plan to utilize a pantograph and either a Dremel with a flexishaft attachment and engraving bit or a pen style engraver (http://amzn.to/2xLiL2I). I have the Dremel rather than the pen style engraver -- not sure if it would be underpowered or not.

Hi,
With the new split step Drum parts can you tall me the settings for infill, resolution & support please? I have probably 5/8 parts printed
Thanks,
Jeff

Lower part: 20% infill at 0.2mm layer height. 30% support infill.
Upper part: 30% infill at 0.2mm layer height until 16mm height and then 100% infill from there on up.

Printing now,
I just want to thankyou again for making such a wonderful model available for us on Thingiverse!
Jeff

OK,
Thank you!
Jeff

how do i get the right size for the dxf files thanks

The dxf files should already be scaled to the size they should be. However, I noticed that when I imported them into the design program for Cricut, that they didn't look right, so I exported them as a highly scaled up png image. I then imported them to the Cricut design program and scaled them back down.

what can i use to print the dxf files on normal printer thanks

I used qCAD to create them (https://github.com/qcad/qcad) to just view and print the files, you can use https://viewer.autodesk.com/

I was just looking at printing and realized that at least one of the files I uploaded has lines not visible against a white background. I will update those soon.

can u sell me all the hardware needed pls

Do you mean all of the non-printed parts? The Bill of Materials spreadsheet contains links to where those parts can be found.

hey i have a issue i can print one part too big how much for u to print this thanks Main_Axle_and_Step_Drum.stl

how much for a finishedone if u sell it thanks you i can put together so is it cost less

Thank you
0490710840

I put up an alternative to the Main_Axle_and_Step_Drum.stl and main_shaft_-_main_shaft_bottom.stl recently for supporting smaller printers. They are Step_Drum_upper.stl and Step_Drum_lower.stl connected with three copies of step_drum_joining_pin.stl with some superglue (or any cyanoacrylic glue)

Thanks for taking the time to create this masterpiece and extra thanks for sharing it. I never heard of this type of calculator until I stumbled across Adam Savages Youtube video on it. I especially like the box you made to house it. This is being added to my 'must do' list after I improve my 3D printing skills and 3D printer. Thanks again. Keep up the great work!

Thanks, I appreciate it!

The box was actually made by https://www.etsy.com/shop/cocobolostudio. I didn't intend to take credit for it and I noted this in the comments of the video.

that's an awesome work you did, i always wanted to have a curta on my own, and i never could. so i'm drooling for your model since i've seen it on adam savage's tested. it actually was the final argument making me buy a 3d printer
i'm looking to make an actual lifesize of the curta not a giant one, as i wish it to be easily carried around, so is it possible? or will it be difficult to scale down because of tolerances? and, if doable, how should i adapt both printed and non printed parts?

anyway i'm gonna make one giant too because i'm craving for one.
again this is an incredibly awesome work and you're a dedicated and talented awesome guy :)

Thanks for all the compliments. It wouldn't be possible to build a working 1:1 scale Curta by pushing plastic. One might be able to go down to 2:1 with an SLA printer, but scaling down isn't as simple as directly reducing the size in your slicer (search the comments here for more info).

To go 1:1 the Curta would need to be built with the original materials or something with equivalent strength and rigidity (not sure what modern materials could approach that). The parts are incredibly small and tolerances are very tight, so AFAIK today's CNC machines wouldn't cut it unless you used a watchmaker's CNC machine which is incredibly expensive.

I would like to attempt it and I do have some ideas for approaching 1:1 scale, but I would probably still need a home machining shop for some of the work.

Thanks you for the answer it proves how dedicated you are for your project and that you diserve the compliments :)

I get it, it's not easy to scale it down, as expected.
I'm not aware of all technical subtilities now, but i'm about about to get a formation in machining, so, if i'm lucky enough to get it and lucky enough to be allowed to use the CNCs for personnal project, i'll maybe try to port your project to full metal and eventually scale it down to 1:1.
Be sure that if i do, i'll happily update you on the work and give you credit back

If you are able to cut a 1:1 Curta on the CNCs, I bet Mr. Savage would be interested in that :)

No doubt he would! Didn't thought about it but now you got me twice as much motivated to do it. :) Even if it is not doable it'll be a lot of extra learnings to show at the end of my formation.

Thanks for everything and keep up with the good work!

My next major 3D printing project will be your superb Curta Calculator design. I see in the BOM the resolution things need to be printed at - but it is not clear what nozzle size I can use throughout. Can I use a 0.4mm nozzle to print EVERYTHING or are there pieces that need a smaller nozzle size?? I am assuming that everything can be in PLA - again, please let me know if this is not the case. I intend printing the outer case in black PLA to minimise the painting required :)

Yes, a 0.4 mm nozzle should have you covered. I did have to reduce extrusion width on a few parts to help S3d with it's slicing. PLA is what I used for everything.

If you are going with black PLA to reduce painting, I suggest also printing the selector knob, the upper portion of the selector shaft, the carriage knurling, the carriage cage, the results dials, the clearing cover, the ring under the crank collar, the crank collar, the crank itself, the crank handle, and the pin screw for the crank handle all in black.

Many thanks for getting back on this so quickly :) This is going to be a GREAT project. I already have the black type 1, the black type 2, and the grey type 2 Curta calculators - so I HAVE to print out your version to complete the set :) As I have original Curtas I am of course aware of the effort you have put into this 3D project. To say that I am totally amazed is a massive understatement!! Thank you for all your hard work.

This is just insane. The amount of work you have put into this is just awe inspiring. Until the Adam Savage video I had not even heard of this device but now I really want one, real or 3D printed.

I know the feeling. I got started on this project after I saw https://youtu.be/loI1Kwed8Pk and had the same desire. I checked eBay and realized that the prices were higher than I wanted to pay for what is essentially a fun conversational piece / paper weight. Sure it's functional, but I wouldn't exactly carry it around to do math. I decided to print a working portion of the device, but later I got pointed to the engineering drawings which allowed me to build the entire device with all of its functionality.

I've looked through both your videos and the unboxing with Adam Savage, and I never saw the use of the upper ring of the calculator (the one labelled 1,2,3,4,.....) that controls multiplications of 1's, 10's, 100's,....Is this feature in this model? The real overarching question is, does this 3D printed model truly replicate the true Curta Calculator? Can it do all the same operations?

Thanks in advance...absolutely love this idea and will be printing my own for sure!

Yes, that feature is in the model. The model has all functionality of the original including the decimal place based multiplication (on computers this is called a shift operation since the digits get shifted over) as well as the safety features: the anti-reversal pawl (preventing reverse rotation), the ring on the main shaft that prevents the calculator from shifting between addition and subtraction mid-operation, the ball bearing that prevents the carriage from being rotated mid-operation, etc (too many to list).

Wow...just wow...so impressed man, can't wait to start this project!

I wonder, to get down to a 1:1 scale, if you had all the delicate and small shafts, axles and gears metal sinter 3d printed through a company like shapeways, then do the rest plastic on a home 3d printer, you could end up with something very much like the original without the several hundred to thousand dollar price tag of one on ebay.
Actually with modern cheap sinter metal parts, and robotic manufacturing and assembly, a company could probably make novelty replica curta calculators far cheaper then the originals without inflation. Now wouldn't that be cool, maybe even as a crowd funding limited run or something.

Good idea, and I looked into it before. The only material Shapeways offers DMLS is Aluminum which isn't cheap. Just the main body is over $100 with that process. Also, some of the parts require steel. The steel Shapeways offers is steel powder with a glue binding. That binding is then replaced with bronze. The result is about 60% steel and 40% bronze. They also state limitations about size that might be problematic.

Ive been playing around with uploading some of the different STLs at a 1/3 (so 1:1 scale) up to your scale and with the steel a lot of the little counting gears and shafts are anywhere between a couple of dimes to a couple of dollars per part before you add on labor, and only the few big parts like the step drum (which could be separated from its axle) where closer to $20 dollar material cost (at 1:1 scale). Most of the price is a labor cost per part which can be mitigated by nesting all the part needed on one or multiple big mesh's (like how plastic model kits come where you have to cut all the individual parts away.) I think all the critical part could be gotten at good enough quality to value ratio around the 1.5:1 scale. and with metal for the moving parts at its core it would be much more durable. the housing, handles, main counting body and other such large or static part can be printed on a 0.15mm or 0.25mm nozzle. I think I'll try to make that work after I get a large plastic one done first.

That would certainly be an interesting build. Let me know how your progress goes.

Is a 0.25mm nozzle required as specified in the title of your OnShape document? Can we get away with a standard 0.4mm nozzle?

Have you considered adding bearings/bushings and changing out some of the 3d printed cylindrical parts that act as bearing surface for metal (aluminum?) rods to reduce friction and ware?

The 0.25mm nozzle was originally required, but I made changes to the few parts that needed a nozzle that small and managed to make it printable with just a standard 0.4mm nozzle.

Which points in particular were you thinking of?

I went back through your build video, and I can't seem to find the bit where I originally identified the area where I thought bearings would be a good alternative. Maybe I'll come across it again. However, my general philosophy is not to over-rely on 3d printed parts when I can buy stronger, more precise standard hardware instead. I was thinking the support shafts/columns could be 4mm threaded rods glued into a 3-d printed cylinder so that you don't risk over tightening the screws. I feel like the zero-positioning pin could be aluminum as well. There are numerous places where you screw bolts directly into plastic (tens bell spring, anti-rotation-plate, transmission shaft lock ring, etc). While it may be overkill, I'd have used heat-set inserts in these areas rather than tapping the plastic itself.

Additionally, the main crank should be split into 2 parts. If you remove the shaft that the crank handle attaches to and make it a separate part, you can make the handle MUCH easier to print; you can put the top surface of the main crank on the print bed and print it upside down without support. If and when I make one, this will DEFINITELY be something I do. (I may also make that shaft for the crank handle out of aluminum, but I realize that's not an option for everyone.)

Would you be opposed to me forking the design?

My goal was to keep the Curta as close to the original design as I could. I have no problem with you forking the design.

That's fair. Thanks!

Comments deleted.

What 3D printer did you use?

For the first Curta I built, I used a gMax 1.5 printer that I sourced and built myself (my first printer, but the second printer I built). The second Curta was built on a Triple C-Bot I built (very similar to the D-Bot here on thingiverse -- https://www.thingiverse.com/thing:1001065), but with three lead screws driven by a single stepper (the triple c-bot is here: http://openbuilds.org/builds/triple-c-bot.1757/).

D-Bot Core-XY 3D Printer

Simply amazing work, congratulations from Brazil !

Thanks, I appreciate it!

Just watched the 'Tested' package delivery/opening for Adam, I had been following your progress for quite a while and was happy to see you made one for Adam. What a masterpiece and a nice touch to deliver in the beautiful wooden box! I too would like to give this a shot with SLA at 2:1, but know once I get started, I will be in for a long project. I can't imagine the time you put into modelling the 600+ parts it took to build this beautiful computer, I just wanted to thank you for sharing such a project! Stunning work all the way around, maybe the best 3d printed project I have ever seen! Thank you, -j.

Yup, I have made two now. The first one for myself (currently unpainted), and one for Adam. The box was an idea I had after watching him get excited about weathering a box he had custom made to fit something. He talked about his love for boxes, so I knew I had to deliver the Curta in one.

2:1 should be a challenge -- I look forward to seeing someone log their success or why they fail. Failures can be very enlightening.

Modeling took about a month. Luckily for me, many of the 600+ parts from a Curta are duplicates or near-duplicates. There were only around 100 unique parts to model and many of those were pretty simple. Some that I enjoyed doing were the teeth of the step drum -- I made one sketch with all ten teeth and then extruded each slice of the step drum by selecting a different number of teeth from the sketch for each extrude.

Thanks for your interest and good luck on the 2:1 scale Curta. Please keep me informed with progress!

Hi, how much it weight ? Just to approximate the number of spool I'll have to buy..

The weight by itself (3 lbs or 1.36kg) is a little bit misleading -- the weight includes a bunch of non-printed parts (screws and nuts mostly) and doesn't include a bunch of support material that is required. It can be done in about two spools, but getting three would be safe.

What type of plastic did you use to print this? Just standard PLA?

Yes, standard PLA

Is there a description somewhere of your hardware tools, software tools, and process?

Yup, check the build manual listed under the files. There is also an instructable with basically the same content as the build manual

Just seen this on a Tested, what an amazing build Marcus. I'm proud to say I own an original Type 2 Curta in my collection of oddities. I tried to download the BOM but get a 404 error, any chance of a new upload of the BOM please? Many thanks.

Thanks! The link in the description was old because I had updated the file. The BOM in the files list was correct. I've updated the link.

Many thanks, I should have just downloaded all the files in the first place.

When I get my 3d Printer back to a working state then I'll do this!

How did you get that perfect finish on this?

I mostly followed Joel Telling's video on painting Harry Potter wands (https://www.youtube.com/watch?v=pnqntteQx80) and added a bunch of extra sanding between coats of primer paint the actual paint, and a clear coat. Between the black and the clear coat I did some wet sanding with 1500 grit sand paper.

Firstly this is awesome, wanted one of these since I knew they existed. Thanks for putting in the hours of designing and sharing

I was wondering what is the odds that I can print these parts at 60% scale? I have a custom prusa i3 style printer set up for extreme tolerances and small parts so using a 0.15 mm nozzle I am confident that I can print the parts to fit, the only concern I have is with ratios and the moving parts. If my logic is correct, it should work as long as everything is scaled equally?

once again thanks for sharing!

60% is close to 2:1 scale instead of the 3:1 scale it is currently at. The hard part about scaling is that you would want to scale everything except the tolerances I added between parts -- otherwise there would be a lot of work to manually fit parts (there already is). To do that you would need to visit my OnShape 3:1 Curta document and make a copy to scale it down. I modeled the parts to 1:1 scale, then I used formulas for most of the tolerances and finally applied a 300% scale transformation so it shouldn't be too hard to alter those tolerances and the scale operation to be for 2:1 scale... not hard, but a lot of repetitive work.

Some concerns I have about scaling it down are:

  • Part strength -- particularly the main shaft. At 3:1 scale I broke the main shaft a few times when I over-stressed it (mainly because parts were misaligned, but still...). At 2:1 scale it will be easier to over-stress it. Also at 1:1 scale some of the parts are too weak to function properly in plastic such as the selector shafts. I'm unsure how that would work at 2:1 scale.
  • Transmission Shaft rigidity -- The transmission shafts can bow under enough pressure and skip teeth on the step drum. That causes the result to be off by however many teeth are skipped for that digit. This usually happens during carry operations -- especially ones that cascade through the digits such as for subtraction. At 2:1 scale the transmission shafts will be thinner and even more prone to bowing under pressure.
  • Non-printed parts -- I spent a lot of time finding the right springs. The spring rates don't always seem to quite scale directly and I had difficulty finding acceptable equivalents at 3:1. You may need to experiment to find the right ones at 2:1. I also had trouble finding some of the balls used and ended up using a different size for the ones I used in the selector knobs in order to make it easier on others which required altered models. Finally, the screws and nuts used are not scaled exactly 3:1 since for many of the screws it would have put them between standard metric sizes. At 2:1 you'd have to walk through the models and engineering drawings and alter sizes to match the closest metric size to the scaled screw size. For instance, the nut at the top of the reversing lever is M1.4 on the original. At 3:1 it would be M4.2 so I altered the models to be sized for M4. At 2:1 it would be M2.8 so the closest would be M3.

All that said -- don't let me stop you if you want to try it. There were a few posts around when I got started on this project that said 3D printing a Curta couldn't be done.

Thanks for the quick reply, it would be a challenge to print a smaller one, ideally, I would like to print a 1:1 scale Curta but I'm pretty sure 3D printing will not be capable of that for another few years. The strength of the parts you mentioned would always be an issue and thanks for sharing your experiences.

As for the springs, I have a few suppliers that should give me enough variety to find the correct springs. The other hardware such as the nuts and bolts, I am considering to adjust the scaling, for example, scaling to 65% instead of 60 to compensate.

thanks again

Yea, I think a 1:1 scale Curta may require the materials that it was originally made with. Some of those materials can be 3D printed today, but I'm not sure it could be done at the size with the precision that are required. Even if it could be done today, those machines are way out of my price range. If the tech isn't up to par today, you are correct that it might be in a few years, but even then the price would likely still be out of range. I do have some ideas regarding a way to approach 1:1, though. It requires a combination of techniques / processes and only a part of that is 3D printing.

McMaster Carr is the main place I knew of to look for springs. I ended up finding a couple on eBay. The hard thing about McMaster Carr is that it's all in imperial units (I'm an American and I really wish we'd just get on the darn Metric bandwagon). I did find some places on the net that had springs closely matching what I needed, but they only supplied in bulk... grr...

For the nuts and bolts I recommend thinking of it as calculating what standard size is closest to the scale you're attempting rather than scaling them to a particular percent that matches a standard size. It may already be what you were planning and it's a small difference with the same result. However, it makes it easier to think about which means less likelihood for a miscalculation.

I just saw the video of Adam Savage receiving one of your Curta computers and realised I haven't responded to your comments.

I am currently still studying engineering so I have access to some interesting equipment and people with the skills to reproduce a 1:1 scale Curta, although this would take a fair amount of convincing and I would need funding. So, for now, 3d printing with some machining is the best I can do.

I am in South Africa so large chain hardware stores are almost nonexistent but smaller owner run and own hardware stores are generally quite useful for finding the correct springs so it will take some shopping around but I think that part will be possible.

I was considering scaling all parts before starting construction and possibly assembling the calculator in CAD software to check for clearances, tolerances and ensuring the nuts and bolts will fit. This way if I print all the parts after scaling and the virtual assembly I should avoid miscalculations.

Yes, a virtual assembly helps a LOT. I avoided many time consuming reprints by doing that... although I still had some time consuming reprints I had to do, just not as many :)

I bought a 3d printer just to do this project. I have a little more work to do to upgrade the printer before I'm happy with it, and need more practice before taking on a project this big, but I'm anxiously awaiting the day I start printing...

Bravo on taking on such a big project for a first experience! I'm very happy to have inspired so many people.

I'll be watching the Curta thingiverse discussion group. If you run into issues you need help with, I have a troubleshooting topic or you can just pop in to show off progress or an end result.

I am soooo doing this one. I've been fascinated with those for years, and unfortunately they are quite expensive. Thank you for your work kind sir. As soon as I finish printing these accessories and prusa printer parts.

Awesome, I look forward to another Curta make!

It's people like you that cause unrest. I am obsessed with the Curta calculators and now I have to print this and play with it. I can't stop thinking about it. BRAVO!

Here via the Make:magazine article, and from there the reddit post (which i sub to but apparently missed when it first went by). Just saying hi and congrats for a great model, it's truly a demonstration of how far the tech has come and what patience and determination can do to your hobby. I hope to get around to building it one day!

Welcome and thanks for the compliments!

Hey! This is probably my favorite thing on thingiverse, and my math professor dad (who I want to give this to as a gift) loves stuff like this, do you think that you'll ever make a version that is the original size?

If I do, it almost certainly will be made from the original materials -- I ordered a 1:1 scale selector shaft and selector knob from Shapeways. The parts work, but the fingers on the selector knob are so small and fragile that it wouldn't hold up to use. The selector shaft is like a toothpick made from plastic with the helical groove and divots in it, so I'm afraid that would snap in time too.

I have a 200x 200 build plate with a 180 height, what items need the 220 height so I may find a way to print diagonally or outsource to get the full height?

The update is now up. There is now an option to print the step drum in two parts -- Step drum upper and lower. There is a pin to combine the parts (print three of them). Just use a bit of superglue to combine everything.

I have an update coming to reduce the height requirement on the printer from 220mm to 170mm. See https://twitter.com/marcuswu/status/904507501181358080. Unfortunately, it will require another day or two to work out an error I introduced before I can test and then release those updated files.

I have a extra large height with a new printer, but now I'm just going to be closely watching while I gather resources and start fall break when I can get a nozzle set for small parts and have the printer steps calibrated. The thing is once they are, I should not adjust it until it is fully printed.

but bringing the printer settings closer to the mean will increase popularity.

I wish I got to have my own tv show for years then get to buy whatever I want fr my own, slightly smaller tv show.

The models should be printable on a 0.4mm nozzle which isn't anything special. The design did originally have a few parts that required a 0.25mm nozzle, but I updated the design between my Curta and Adam's to remove that requirement.

The main shaft and step drum requires the height. The upper and lower housings require the full width and depth specified while the lower housing requires 170mm of height. The transmission shafts need 170mm of height as well. After the lower housing the next widest / deepest part (the upper sleeve) requires 143mm of width and depth.

Fantastic project! I too came here from Adam's unboxing. Question: Is the main axle and step drum supposed to be printed as one item? I have started printing the parts now, and have completed the bottom housing (almost 50 hours) and about 15 other pieces.

Currently the step drum and the upper portion of the main axle are combined into one part. The lower portion of the main axle is a separate print that slides into the bottom of the step drum.

The main axle and step drum combination are apparently taller than many 3D printers can print, so I have a version where the bottom part of the step drum is combined with the step drum and the step drum is divided in two near the top. This would reduce the required printable z-axis height from 220mm to 170mm (see https://twitter.com/marcuswu/status/904507501181358080). That design also significantly reduces the amount of support material required for the step drum which also reduces the print time. I think the original design required around 12 hours of print time for me. It is now around 6.5 hours.

Unfortunately, while putting it together yesterday I noticed that I introduced an error into the angle of the main axle when I combined the two so I cannot release those files yet. If you can print the existing models, I suggest you do that unless you can wait another day or two on the updated models.

Thankyou,
I use S3d and separated the two pieces and printed them individually but I think I will wait for your revision and see which works best.

How many individual parts make up this print?

Dare I ask how long it takes to print all the parts ?

I calculated it out and it's around 9 days, 14 hours, and 44 minutes non-stop printing on my printer. That's assuming no failures and that someone is there to immediately remove one print and start the next. Filing and sanding the parts to fit properly and assembling it takes longer.

Very nicely done. Really beautiful work.
That's a lot of parts surely requiring a lot of work to get things to function together. I will be hoping for some printing time soon to have a go at this myself.

Awesome, thanks!

Note to everyone, I have a thingiverse group (https://www.thingiverse.com/groups/curta) where I would love to see progress photos and any questions people may have building theirs.

Hey Boss,
I'd really like to print one, but I'd like to print the most up-to date version. Any chance of an update soon? I'd be more than happy to work on some issues you're having. I'm proficient with Fusion360 and have 3 printers of my own. Currently work as an R&D engineer and just love the history behind the curta. Ever since I saw your post on Reddit, I've wanted to print one and the time is now.

Thanks again for your work, Luke

Just uploaded an update. The BOM is updated, paint masks are added, and an initial draft of the build manual is added. As far as I know, these files should now be correct and the main changes left are to the build manual as I find things that need better wording and as I am able to add more images to it. Feedback on the build manual is desired and welcome.

You are the man! I can't wait to get started. Thank you much!

I do have some updates coming soon as well as paint masks for numbering and lettering on some of the parts. I was out of town for a bit for a wedding so those have been on hold. I will try to get those uploaded today.

If Thingiverse counted multiple likes, I'd click this project every time I went on line. Amazing!

Thanks, I appreciate it!

I've updated the description of this thing to list a poll (https://docs.google.com/a/digitaltorque.com/forms/d/e/1FAIpQLSeJQcq5njLh1_Z-IPOROXWmYAR7QqbMc7tr924hxTVYikhf6Q/viewform?c=0&w=1) on how you would like to see build instructions for the Curta. Please fill this out -- it's just one question.

Wow! This is incredible.

I am waiting until the instruction set is complete, but I am definitely watching this. If you have a video I would love to see it in action.

I finished the second Curta and took tons of pictures on interval while working on it. I will be using those to document the build process soon. Here is a vid I took recently: https://youtu.be/ShFkJgck6Pw

Hi,
Really great that you have made the effort.
I was trying to sort the files according to the POM and have few problems. I couldn't find few files (and obviously had few left that didn't fit into the POM table).
item # 2 --> I found 10061, but 10029 not really
item # 70 --> is it the "digits axle"
item # 71 --> ?
item # 72 --> is it the "main shaft pin", there is no number so I can't compare it with the original drawings

I'm thinking to build it or at least give a try. I have ordered almost everything except two springs.
How strong should "torsion spring for zero position lever" and "torsion spring for anti-reversal pawl" be? I have real difficulties to find the matching ones and was wondering if I could bend something similar by myself.

Do you have more pictures from the assembly process? Clearly it will be a huge effort to write instructions, thus I would appreciate already when I could see some pictures of the assembly process.

Thanks a lot!

10061 is the selector shaft and 10029 is the cylinder that goes around it with the number markings on it. I combined the two and then split the selector shaft in two (to reduce the support required). The selector shaft is named Selectorshaft-_selector_shaft_bottom.stl. The top of it is called Digit_Selector_Axle.stl.
Yes, #70 is the digits axle.
71 and 72 are mainshaft-_Main_shaft_pin.stl and Part_Studio3-_main_axle_dowel_rod.stl -- the longer one is to connect the main axle to the crank handle and the shorter one is to connect the zero positioning disc to the main axle.

The two torsion springs were the most difficult for me. I ended up making them myself the first time around, but not in a way that would be easily reproducible. I did some searching and linked to mrspring.com and McMaster Carr to items that should work, though I have not tried them yet. I'm working on building a second Curta -- if they don't work, I'll update the BOM with something that does.

I don't have a lot of pictures from the assembly process yet, but I will be taking a lot in this second build. I'm also working on assembly renderings from the 3D models.

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What a terrific project. I'm starting now on a 3D print of the 3X version but wondered if you had given any thought to machining the 1X scale model from aluminum, steel, or brass bar stock? The idea intrigues me though it seems like an ambitious machining job.

I would love to, but I don't have the tools (Mill or lathe) and I don't have the experience working on them either.

Thanks - I have both lathe and mill, but as I saw it looks like a really ambitious machining job so I'm starting with a 3:1 scale 3D print first on my Zortrax M200 printer. So far it looks like larger pieces are best done in PLA+PHA because that doesn't warp, and smaller parts are better done in ABS because those print better with my printer. How well does your 3D print model work?

Yes, it is a pretty ambitious machining job, but many of the parts are pretty simple with a few complicated ones in the mix (the selector shafts come to mind). I hope to one day learn to machine and build a 1:1 scale Curta.

Mine was working quite well until I made the mistake of lying it sideways on my desk. It rolled off and landed with a sickening crack. Multiple parts are broken, but I haven't had a good chance to reprint and repair because I am busy working on a build manual and a commissioned copy. I don't think I will do any more commissioned copies for those reading... I didn't think I would even do one, but that is a whole different story.

For me, some of the harder parts to print are those selector shaft parts and it seems like those would be really simple to machine, even at 3:1 scale so I may give that a shot if the printed parts have problems.

Really sorry to hear about your damaged model. I did the same thing with a large modular arm but only a couple parts broke on that so fixing it wasn't too bad. It's especially sad on something as complex and time-intensive to build as your Curta calculator so good luck on getting it repaired.

It must be tough to get a fair price on commissioned copies of the Curta - most folks have no idea how much time goes into the printing and post-processing, let alone the time to design it in the 1st place.

A fair price for a 3D printed Curta with all the time necessary to manually fit all the parts would run (significantly) more than a real Curta. In this case I'm doing it for someone I couldn't say, "No," to (in fact, I was honored to say, "Yes
) and plus I get a trade for a real Curta and some publicity too which will be fun.

I really didn't have much trouble with the selector shaft parts. The peg on the top of the selector shaft and the peg at the top of the bearing that the selector shaft sits on did break a few times. I printed those at 100% after having them break. I have considered (and still am) printing them with a hole instead of a peg and fitting a pin in its place. The pin could be a metal one, but I've had good experience with printing pins horizontally that are pretty strong and that would keep more of the Curta 3D printed.

Not really a big deal on breaking my Curta -- I'll reprint the parts when I get time and I've gotten pretty good at taking the thing apart and putting it back together. Really, the time consuming part has been printing and fitting the parts (more fitting than printing). I am preparing the external parts of my Curta for painting and that also takes significant time to get it right (especially with the knurling on it). I also need to find a good way to get custom made decals or paint masks to get the numbering and lettering on it before I can consider mine done.

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Nice that you get an actual Curta and publicity out of the deal.

My Zortrax printer maxes out at something like 80% fill (they only have options for low, medium, high, and maximum) so solid is not an option. I also thought about using metal pins on the selector shaft parts if the plastic ones break off. It would be easy to drill holes in the applicable parts with a lathe and there might be an appropriately sized dowel pin available. By printing those parts horizontally, do you mean on their side? I don't think that would work at all well on the Zortrax but maybe you mean something else.

By the way, which brand and model of 3D printer are you using?

Yes, on their side. I can't print a larger diameter than about the size of the support columns on their side due to the angle of overhang at the bottom of the cylinder diameter and I have to use a raft or a big brim / skirt. I also slow down the print to reduce the likelihood of longer cylinders warping with the small contact area. For a small pin like the ones we are talking about or the carry pins for the results dials, I print them on their side on a raft then clean them up with a needle file afterwards because it isn't the best geometry to print that way, but it does make the pin much stronger.

I printed the first Curta on a modified gCreate gMax 1.5 (not the plus version). I am printing the second one with a triple c-bot (http://openbuilds.org/builds/triple-c-bot.1757/) running on a replicape (http://www.thing-printer.com/product/replicape/). Not having a large print bed moving back and forth quickly on the y axis for small features or infill in tight areas is a help. I am also enjoying the reduced moving mass of the core-xy. I am printing at twice the speed and getting significantly quieter operation and a better quality result.

Thanks for the info on your printers. Looks like they (or probably the slicers used) provide some nice capabilities that I don't get with the Zortrax. Oddly enough the 10207, 10208, 10209, and 10216 shafts print vertically pretty well for me so long as the raft sticks to the print bed. I'm having major problems with 10220-410003 and similar sleeves for those parts though. That little V feature that protrudes from the inner sleeve wall toward the center of those parts fails to render in my slicer, apparently because the slicer doesn't recognize a wall less than 0.5 mm thick and can't make a wall less than 0.9mm thick. I'm fiddling with slicer settings and changes to the Onshape part files to see what I can do to fix that but am not hopeful.

I just updated those parts (10218, 10219, 10220, 10221, 10222, and 10230) to be more easily printable with a larger nozzle. On my slicer I did have to reduce the extrusion width some, but it should print without a 0.25mm nozzle now.

Thanks - this comes at a good time for me as I have time to try those parts again and was about to see what I could do in Onshape. I'll report back in a day or two on how it goes for me with the new parts.

I've already printed the zero positioning disc and those little teeth seemed to come out pretty well for me. Time will tell if it works as good as it looks.

Thanks again for the revised parts - I really appreciate the effort.

I have been busy printing a second Curta and have been needing to print those for a while, but my 0.25mm nozzle is clogged and I don't have a tool that small to clear it out (tried some other methods already). So the updates weren't entirely altruistic :).

Currently I'm printing the large lower housing. On my old printer that was a 60 hour print. This one should finish in just over half of that time... assuming it succeeds.

There is no reason the curve needs to be a single wall (I just followed the engineering drawings directly) -- it can be capped and filled so that the outside of the is a cylinder and between the 'V' and the cylinder is filled with material.

In addition, there is also no reason that the spacers that make the part thicker can't reach all the way to the bottom of the part so that there are no thin portions of wall. I avoided that issue since I have a 0.25mm nozzle. If I get a moment, I can make those changes or if you have already made them, if you send them my way I'll update the files and add credit to the description.

In fact, there is only one other part I can think of I really needed the 0.25mm nozzle and that was on the zero positioning disc. The toothed portion of it that combined with the anti-reversal pawl prevents backwards rotation doesn't print with a great edge on the teeth when printed with a 0.4mm nozzle. It may have worked, but I didn't want to take a chance on it. My new printer got better definition with a 0.4mm nozzle, but I'll have to test it to see if it's good enough. I'll be able to check that out soon.

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You just made my dream ! I have always wanted a curta !

For anyone watching, I just updated the printed files in the BOM to include details on how they should be printed -- layer height, infill percentages, etc. For parts that I said to print horizontally, I did that for strength even though they don't come out as round. Sometimes filing is necessary to smooth those out and fit them with other parts. There are two types of screws that need to be printed -- one for each of the selector knobs and one for the main crank handle. Those along with the tops and bottoms of the frame supports need to be threaded. I encountered a lot of splitting of parts when putting them through a die before I found that if I filed the layer lines down, it eliminated that problem.

I hope to begin writing up an actual build document soon.

Awesome job! I just decided to search for this to see if maybe someone had made this amazing piece of engineering printable and lo-and-behold you put it up just 5 days ago! I know what I'm printing next!

This is Amazing!

Thank you very much mwu for sharing! I've been watching your updates on your blog for months, hoping someday soon you'd release the files.

Mechanical Calculators are hobby of mine, and I've always dreamed of seeing and using a Curta in person, or, by some miracle, owning one myself. Looks like my dream just became that much closer to reality!

This is amazing work! I think people sometimes underestimate the mechanical marvels these devices were, the Curta being the apex of their design ingenuity. Thanks for shining a light back on a page of history many have forgotten!

Many Thanks,
Dan I.

I wish I could have gotten it released sooner -- real life intervenes more than I would like :) I also wish I had a build guide, but that will take longer.
Thank you for your interest and support!

Quick question. Is it possible for the chrome steel 5mm ball bearing that's available on Amazon to replace the 5.3mm steel shot or does it have to be exactly 5.3mm? Regardless, THANK YOU for posting this (I'm Mr. Pute on YouTube who's been bugging you about it)!!!

The 5.3mm ball is used with a spring to snap the selector knobs (used to input a digit) to a number so that it cannot sit between digits. Given that its main function is just to sit in the detents in the selector shaft, the 5mm ball will most likely work.

To be sure, I can update the selector knob's hole to be 0.3mm smaller to eliminate slop caused by the smaller ball. The springs listed for the selector knobs are small enough to account for the smaller hole so that won't be a concern.

Good suggestion -- I was thinking that steel shot would be a problematic part since the only way I could find it was an entire bag.

Awesome! I'll hold off on printing that part until you make a modification. I'll order the 5mm ball and confirm whether or not it works properly after I assemble. I'm looking to make two of these (one as a Christmas present and one for myself) within the next couple of weeks. Thanks again!

It is updated now -- both the model and the BOM to reflect the new ball size.

It's very ambitious to make one of these before Christmas. Significant time is necessary to manually file and ensure proper fit of each part. I also had to do a lot of calibration to ensure carry operations work properly. Good luck -- Also I don't mind answering questions along the way.

Fantastic! Thanks! I'll keep you updated on how it goes.

cant wait to print this

Now I can own my own one. And I still know how to use it. Thanks ;-)

Now I can own my own one. And I still know how to use it. Thanks ;-)

So I'm not the only one who dreamed of owning an over-sized Type I. This is a work of art!

Thanks :). The over-sizing is simply a result of what my printer is capable of. If I had a mill and lathe and the skill, I would have made one at 1:1 as close to the original as possible.

No, it is perfect! I am a huge fan of up-scaled machines and cut-aways, so this is my catnip :)

Simply amazing work, congratulations!

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