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Ask questions about your build! Having trouble printing a particular part? Having trouble getting parts to fit? Trouble sourcing non-printed parts? I am here to help

I have completed print and it was awesome challenge for me..happy that I am got success so far.
I assembled everything together and everything works fine so far.
I splitter most of the big parts to print without supports. And glued it together. Thanks a lot for sharing the design files.else print will.be impossible for me.

I have some doubts

  1. How to paint letters with such detail?
    2.the largest spring, 1.8x28x40 or similar is not available anywhere near me and no delivery to my locality. Any suggestions for this?

Any tips on making the carry lever springs? When I use 55mm of wire the center of the spring seems too big but when I start using a smaller length of wire the center becomes too small to fit in the bearing slot. Do you have any pictures of the carry lever assembly?

The carry springs are difficult. I typically start off using the tool to create the initial shape and then fine tune with pliers. In the attached pictures, you can see how things align on mine. However, test the levers to ensure they pop up and down easily. Double check by rotating the step drum & tens bell to ensure that depressed levers pop back up to their original position. The carry gear should interact with the tooth on the tens bell when pressed and when reset, it should not.

If the action isn't quite right, I adjust the position of the two short legs. As long as they are close, you can angle them up or down as you can see in the pictures. If it is too far off, straighten the legs and re-bend at a different position. Both on the original Curta and on this 3D printed version, these springs and the levers are the most finicky parts. Particularly with 3D printed parts that need manual fitting, it is tough to consistently get it perfect without some manual tweaking.

It's annoying these images are not in line with the post... I created a shared album

Amazing!! thank you for sharing and your contribution!!

Sorry if this was already asked and answered but I couldn't find it anywhere.... what printing material do you recommend? Did you print in PLA? is that nylon

I printed it all in PLA. Some of it looks a little like nylon because it was leftover PLA from another project for a client who wanted a translucent look. If you have a hardened steel nozzle, I recommend printing the transmission shafts in a carbon fiber filament for added rigidity. I used https://www.3dxtech.com/carbonx-petg-cf/

What's the correct orientation for the results dial axles? Should the flat of the little notch at the bottom be touching the lip inside the upper housing. or should it be flat against the cutouts in the underside of the digit cover?

I've tried both orientations (build manual shows them facing down) and if facing down, the clearing cap sits a bit too far away to get some dials away from 1 or 9 and rubs on the digit cover. But if they're up, the results dials are very tight to the digit cover and can have issues binding against that.

Up is correct. I will have to correct the build manual. My prints of the digits cover weren't perfect and required some work to allow the dials to spin freely. It's possible that the design isn't quite perfect either and some of the work is due to that.

Thanks - I had success by carefully shimming the insets in the digits cover and shimming the clearing cap teeth by the same amount. It didn't require much, I used some scrap 0.2mm brim.

In my case the results dials are MMU prints and so are less even on the surface and not as practical to sand down. :-)

I'm in the process of printing the carry levers, carry lever bearings, and making the carry lever springs. Do you have any pictures on how to orient the bearings? There are just so many differences in height that the ones I've printed seem to be ruined when I get done filing/finishing them. Also when printing the levers in the orientation described how do you prevent them from wiggling/uneven layers since they are so tall and thin? How precise do both of these parts need to be?

Hi there! I figured out the gear alignment dilemma (my own stupidity) however upon attempts to slice the step drum lower//upper halves in cura, support is not generated on the teeth. Do you have any tips for getting the program to recognize these overhangs? (I have set it to generate everywhere and 0 degree angle, so it's not that.)

I may have uploaded the files before repairing geometry. I'll see if I can find some time to re-upload that soon.

I am sourcing the wire needed to create my springs but wasn't sure how much length I need. Just trying to cut down costs and buy as little wire as I need. This stuff is cheaper than the amazon linked wire but it is 10 feet.


10' should be enough. The length needed per spring is around 2'. You should have enough to make each spring with plenty of room for learning. It takes some finesse to get right. Wind extra loops for each spring and then bend the legs out and cut it down to where it needs to be.

Be careful making them -- I almost broke a finger when I slipped and the spring steel unwound suddenly on me. Definitely wear thick work gloves.

Great to know! Thanks! I will be careful!

What is the file name for the Collar you reference in the build video at 30:57 and in he manual on page 35, i cannot seem to find it in your spreadsheet?

First of all, this is an amazing design. I've printed everything except for 2 parts. I'm having trouble printing the (tens_carrylevers-_tens_slider_for_results.stl) and the (tens_carrylevers-_tens_slider_for_turns_counter.stl). Could you recommend the orientation in which the parts should be printed? I've tried to print it in the upright position (picture down below) but it keeps failing.

Thanks! I apologize for taking a couple of days to respond. The basic orientation is correct. Here are some tips:

  • If you aren't printing with a raft, add one. I cannot print these successfully without one.
  • If your print bed moves along the X or Y axis, you'll want to align the bottom of the 'L' shape with the movement of the print bed.
  • If your nozzle(s) are hitting the print as the carriage moves, try aligning the levers so they are in single file with the end of the 'L' pointing at the next one.
  • Try slowing it down -- vibrations can make these tip.
  • If you aren't using supports, add them. It doesn't help much, but it will keep those small overhangs crisp and give a little extra footprint.
  • While experimenting, printing just one at a time if you have good cooling (two if you don't) might help.

These can be particularly difficult. Let me know if you continue to have problems. I could add cut-away bracing, but it will increase print time and make finishing them harder. The sides need to be pretty smooth to slide nicely in their brackets, so the bracing would need to be cut away and then filed smooth.

Thank you very much for the reply, I will definitely try these tips and I'll post a follow up after I try these.

I'm having trouble tapping the holes in the main casting (page 8 of the instructions).
I have never done any tapping before.
A test tap I did dug in very slowly, and effectively drilled out a smooth-sided hole, rather than a threaded hole.

I found this guide for tapping metal: https://www.dysoncentre.eng.cam.ac.uk/metal-working/threading/Threading-manual

Should I drill the holes out first e.g. 3.3mm for M4? Some other size?
Cooling or transport liquid?
"half a turn into the material and then a quarter turn back" ?
I bought a set of taps that only has one tap for each size, not 3 different taps for each size. Is this important?

Are there any other options like self-tapping or tap-cutting screws?

No need to drill out the holes. They should be sized appropriately already.

Also no need for a cutting / cooling / transport fluid -- The plastic doesn't really heat up enough to warrant that and I am unsure whether those fluids would weaken the plastic or not. When working with metal, the friction and forces involved can cause the tool to dull and weaken producing even more heat and eventually breaking the tool. It also makes the machining rougher and not as precise. Plastic is softer so you won't damage the tool, but you can build up enough heat to start melting the plastic. This is what may have happened to you. Go slowly -- if you're using a drill, try it by hand. It can be done with a drill, but it takes a very steady hand to keep it aligned with the hole and moving as slowly as necessary.

Yes to the half turn in and quarter turn back. The tap will have flutes cut into it (probably either three or four) which collect the cut material. Doing that quarter turn back helps collect that material so it doesn't collect in the path of the cutting edge of the tap. Not doing this can also cause additional heat or the collecting plastic chips can destroy the threads you are cutting.

One tap for each size should be fine as long as you have the correct diameter and thread pitch for the screws you are using.

I haven't tried self-tapping or tap-cutting screws. I'm not sure how well they would work. They would likely need the same treatment as the tap. You'd also need to find screws that fit into the same holes since these are all sized for metric screws. Something like this: https://www.mcmaster.com/#tapping-screws/=1bgsm3a. This is admittedly one of the tough things about this build. I didn't really want to use wood or sheet metal screws on it because they would require altering the design (I wanted to be as authentic as possible) and because they just don't offer the same aesthetic.

Some additional tips: Keep that tap as aligned as you can with the hole. Putting it in at an angle to the hole will cause problems. The holes around the side of the main casting don't go straight towards the center, they are offset at an angle (they follow the same angle as the slots cut in the flanges of the main casting). Take your time, examine the hole, align the tap, turn slowly, and do the quarter reverse turns every half turn. I tend to not do the reverse turns until the tap is nice and established in the hole and I like to re-examine the angle I'm at after a couple of turns to ensure I am still aligned properly.

The set I have is Duratool D00195 20 Piece Tap and Die Set

I'm having trouble with parts like 10219_-_410002.stl double transmission gear.
This part is made up of basic components "mated" next to each other, but there is still small gaps between the components.
Looking at the bottom, there is the outer sleeve, and a very thin inner sleeve with a key bump.

In Cura, the inner sleeve isn't printed, but the key bump is printed "next to" the outer sleeve, i.e. its path is not joined end-to-end with the outer sleeve. Won't be very strong!

However, in ideaMaker (with the settings I have now) the inner sleeve and bump are printed as one, but the diameter of the inner hole is reduced.

Ideally, I think that composite parts like this should be "fused" or "union"ed together so that there are no internal gaps,
and e.g. for this part the slicer would only see one tube.

Another example: 10207 transmission shaft + gear, there is a tiny gap between shaft and gear ...

What settings did you use for: number of shells, top and bottom thickness?

2 perimeter shells. 3 top and bottom layers for 0.2mm layer height models and 5 top and bottom layers for 0.1mm layer height models.

Hello again,
Question regarding the tens slide bearing, you say to print 100% with no support. Can you tell me the orientation of the part you used as I have printed it on its side and on its back but both times WITH support.

It should be with support. Where does it say to print it without? I need to fix that.

I must apologize, I must have looked at this wrong you DO say with support!

The BOM excel file line 68, also is it printed the with orientation as is when I place the file (on its back)?
On a side note, could you model the case that is shown in the exploded view poster from www.vcalc.net?

Just wondering, what are all the little triangles on top of the counter body for? Also, what does that crank pin do?

If you look at the negative space, you will see channels instead of triangles. The channels fit the peg built into the main body so that the upper carriage cannot sit between digits when you turn the carriage for handling multiplication.

Without the name of the file I am unsure which pin you refer to. There are a few pins that might be called a crank pin. One is at the bottom of the main shaft which turns the zero positioning disc with the main shaft. One is at the top of the main shaft and holds the crank to the main shaft. One is actually a little screw that has a nub on the end for holding the handle on to the crank while also allowing the handle to spin on the crank.

Thanks, as for which pin I meant the top one, but thank you for mentioning all the others. :)

Hi Im just starting the build and im double checking everything. I came across the BOM and found that Item No. 56 Main Body says that "combined with 10016 and 10134 for 3D printing" in the Description... ive looked so many times and have no idea where those parts are.
And also if printing the Step Drum (Main_Axle_and_Step_Drum.stl) in one piece, do i have to print the Main Shaft Bottom??

The main body is already combined with those two parts -- you don't need to worry about them. If you're curious about them, you can check out the engineering drawings -- 10016 and 10134. In the original Curta, they are forced fit parts that don't move in relation to the main body, so I combined their shapes with the main body.

Yes, if you print Main_Axle_and_Step_Drum.stl, you will still need the Main Shaft Bottom.

Ok soo what are the print settings for it??
Thanks again

I updated the BOM when I realized that it was unclear: 30% infill at 0.2mm layer height and 25% support infill.
I also fixed a problem with the info for the upper carriage spring (non-printed parts). I originally listed it as, "1.8x28x25mm spring." It should have been, "1.8x28x40mm spring." Hopefully you haven't ordered that yet.

Hi again
Sorry i found a slight mistake in the BOM regarding the number of M4 bolts needed for the Carry Levers... In the build manual it says 25 is needed but in the BOM it says 15.
Also, I thought id ask now, can u please outline which of the rotation lockouts and gears are meant to be glued in place and which are meant to be moving parts. The build manual is confusing to me.
Thanks alot

The manual is incorrect and the BOM is correct. Each bolt holds a carry lever and bearing combination in place.

Ok and as for the rotation lockouts and gears for transmission shafts?

What about them do you need to know?

Which of them are meant to be held in place by the clear nail polish? The manual is confusing to me sorry.

That is determined by the transmission shafts. The ones with grooves cut out of them should have the corresponding gear or lockout fixed in place.

The first shaft from both the results and turns counter shaft groups should have grooves for the lockout gear combinations. The last three results shafts should have grooves for their gears.

Ok thanks alot

is it ok to do 100% infill for the whole step drum upper? Because i am finding it difficult to do a setting change at z.

It should be fine as long as it doesn't curl.

you did use reticlinear for infill pattern right?

Comment has been deleted

I had to print the main axle separate from the lower axle (and step drum). Any tips on alignment of the two? Unfortunately I don't have the Z throw to print together. If needed I will reprint the 2 piece step drum (upper/lower) but I was thinking that I could probably align the pieces once assembled more. Any thoughts?

Is this what you printed? The notch in the top of the lower portion of the main axle helps alignment. You'll just need to make sure you don't have it 180º off.

If you are looking at the step drum upright with the teeth of the step drum to your left, the flat part of the flanged portion of the lower axle should be facing you. The build manual has a photo of the correct orientation (also on instructables).

Kind of lol. I had to split the model to print the tall axle separate from the bottom. So right now I have the lower axle, the upper axle, and the step drum. So I don't have either side of the axle to "key" to the piece.

I may simply edit the lower stl and put in a pin through the lower axle and then reprint just the lower axle. The step drum already has two holes in it, so a pin could go there quickly and easy to align them. Then the pieces will all key correctly. If I do that I will send over the edited stl with the hole in the lower axle.

Was just asking if there was a quick and easy way to align the bearing plate to the flange.

You are correct, aligning the axle to the step drum would be difficult without it pre-aligned. That's why the upper and lower step drum parts divide the axle along with the step drum and use pins to align the step drum parts. The step drum parts act as the key to align everything, the division along the widest part of the step drum allows for a large footprint on the print bed for easier printing, much less support material (by rotating the lower half upside down), and two of the three holes were already there since that was how the plates that made up the step drum were secured on the original Curta.

Yes, you could put a hole through the axle which would allow you to use the hole through the bottom portion of the step drum. That's actually how the original Curta's main axle was fastened to the step drum. The pin was narrower on one end than the other so that tapping it into place wedged the pin into the axle and step drum to form an interference fit (not removable).

Another option is to divide the top portion of the main axle inside the step drum just as I had divided it on the lower piece with a notch to key and align to. So there would be a short segment with a notch cut out of the top and bottom inside the step drum. Then the top and bottom parts of the main axle would be printed separately. That way the division lines wouldn't be visible. However if you do it that way, be careful because the easiest place for the main axle to break is where it interfaces with the step drum. The mate between those should be strong. I typically print the top of the main axle with the step drum and ensure that starting at the last few layers of the step drum leading into the main axle, it's all 100% infill.

Thanks! I will prob try to align it by hand (should not be too hard, I may make a jig) but I have all the measurements. If it fails to work then I will reprint the two pieces. They were easy to do.

I am running into a couple issues. I am using S3d and the gears are slicing weird. What I mean is they dont print as they are supposed to and it shows that way in the preview too. Im not explaining well and I forgot to take a picture so I will reprint if necessary. Also just tried to print the spring clips and they print almost flat. Again in the slicer it shows incorrectly as well in the preview.

In S3D I had to reduce extrusion width on the gears. For my 0.4mm nozzle S3D defaults to 0.48mm extrusion width. Decreasing it to 0.4mm or even 0.35mm should solve that problem. I think I opted for 0.35mm as it allows for better infill in the teeth of the gears. The extrusion width can be reset to default after those parts are printed.

This in fact worked just as you said it would!

Good Morning,
Thankyou, yes I just checked and it is as you say (.48) I will change to .35 and see how it goes. Thankyou and I will keep you posted!

I was always fascinated by the Curta and saw this build on Adam Savages channel, I knew I have to make one!
I started printing the parts but missing some pieces or just overlooked...
In the BOM you have transmission gear listed but I can't find it in the parts list. Is it there with an other name perhaps?
Thanks for this amazing model!

Yes, it has a different file name. I've updated the BOM to add a file name column to make it easier to find those and a couple of other ones.


I am having trouble printing things that have a small surface area touching the bed.
Any tips / ideas or information that can help me start printing?



I used a brim as well or a raft for some of the smallest surface area parts like the pins that I print sideways.


are you printing with a brim ? I normally use 4mm to 6mm
https://www.simplify3d.com/support/articles/rafts-skirts-and-brims/ here it's described what it does. Every slicer has such an option.


Hi !
First things first this is plain awesome. I got my printer a couple of weeks ago and after finding this I'm really into building one myself.

Do you think it's possible to shrink it just a bit ? Lets say about 25% or so. I know , after reading into it, that it's about precision and stability. But I'm a bit concerned about the total size and if I'm going to like it.

I can't judge about the precision but if it comes to stability their would be carbon enriched filaments.

Otherwise what do you think is the most save amount of shrinkage possible ?

75% of 3x is 2.25x -- so it's approaching a 2:1 scale Curta. That's something I have considered trying before.

For printing, one of the big problems you'd be facing is that some of the parts wouldn't be printable with a normal nozzle at that size. You'd have to use a 0.25mm or even 0.15mm nozzle to reach 2:1 scale. In fact, I had to modify some of the parts just to get them to be printable at 3:1 with a 0.4mm nozzle. On my first Curta I used a 0.25mm nozzle for some parts.

For functionality, one of the issues I had with the 3:1 scale Curta is subtraction tends to produce more force on the parts. The weakest part will bend or break. For the most part it is the transmission shafts which bow (but not break) causing steps to be missed. At sizes approaching 2:1, those transmission shafts will be even thinner which would make it easier to bow. Carbon enriched filaments wouldn't help much if these are printed upright as I did. You'd have to print them horizontally and hope they don't curl (they did when I tried).

One possibility for a 2:1 scale Curta is to repeatedly print parts until you get something good (even if it isn't strong) and then mold and cast it with a resin. That should produce pretty rigid parts.

As a side note, I inevitably get a question about a 1:1 Curta -- even DMLS printers probably couldn't pull it off without some machining to finish the parts at which point you might as well just machine the parts from the start. Actually, getting into machining and making the parts at 1:1 scale is one of the things I'd like to do eventually.

PS: I assume your name refers to the command-line text editor. I have to tease a little bit because I used to use Emacs back in the day. I switched to Vim and haven't looked back. :P

Thank you very much on the quick reply and insight of your design.
You're most likely right with the orientation of some parts which open a whole bunch of different problems when they are printed sideways instead of topdown.

And yes it's about a text editor :) not looking back either and I'm not one of those fanatics that try to convince you to switch back ( which you should , but doesn't prevent us to work together in the 3D printing world ;) )

I'll keep you posted once I printed something


On second thought, what crucial parts would you recommend for test printing on lower scale. I'm far off to doubt anything of what you have mentioned because I have utter respect of your work but I'm new to the whole 3D printing stuff and would like to experience it thirst hand were the limits of 3D printing are. ( this also will help in my future designs )


Unfortunately, it's not as simple as just scaling the parts down. If you scale down the parts I've published, you're also scaling down the tolerances / clearances between the parts -- you'd want the tolerances to mostly remain the same while the rest of the model scales. That'll require some CAD work. The models are all available publicly on OnShape (https://cad.onshape.com/documents/57e3f5c529d2af11276b1529/w/eafe4a700fe87f2b71bc3d31/e/f1e5e18535312417d6894ed1).

If you have the ability to make those changes, I would start with the transmission gear sleeves and the zero positioning disc (pay special attention to the teeth -- they must be well defined and sharp enough). The gear sleeves are thin-walled so printing them smaller could be a problem without a smaller nozzle. Be sure to preview what your printer will be doing in your slicer before you go to print anything.

I modified both of those parts to improve the printability with a 0.4mm nozzle at 3:1 scale. Those parts could probably be modified further, but it might require modifying other parts and ultimately lead to redesigning most of the Curta. For instance, the gear sleeves can be widened, but that means that the sleeve may interfere with the step drum's teeth. If that happens, you'll need to move the transmission shafts further away from the step drum a small amount by altering the main casting and the bearing plate. Once that is done, the carriage casting or the digit dials may need modification to be slightly further out from center to match up with the top of the transmission shafts. Then the positioning of each of the carry levers may need to be tweaked and the housing would also need widening to account for the small amount of extra size added to the other parts.

It may be totally possible, but you may also dig yourself a pretty deep hole chasing the rabbit. Now if you have an SLA printer, you don't have to worry about nozzle size and may be able to print those parts at 2:1 scale without going down that rabbit hole. The parts would still probably need to be scaled without scaling the tolerances, though.

Thank you once again for the insight and ruining my hopes on shrinking it ;)

I only understood half of it, which convinced me to stick to your original design, maybe that I pick up this topic again after I have a better understanding of this complex machine.


It may be difficult to follow the names of the parts and how they interact together coming into it new -- reading through the build manual will probably help with that. Also, the part files are named and the OnShape document I linked has the parts named. It probably is a good idea to build it at 3:1 first before attempting to scale it down, though.

Btw, if you want to understand the device more or are just plain fascinated with it (like me), I highly recommend the Curta Calculator poster (http://www.vcalc.net/cu.htm). It has an exploded view of the Curta and most of the parts are labeled. I wish I had that when I was getting started. The names of most of my parts are based on the google translation from the German part name listed on the engineering drawings which aren't always super accurate.