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Remaking a Curta Type 1 Rev 2

 
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thomasmanegiste



Joined: 03 Mar 2025
Posts: 4
Location: France

PostPosted: Tue Jul 22, 2025 6:28 pm    Post subject: Remaking a Curta Type 1 Rev 2 Reply with quote

Hello everyone,

I'm sharing a projet I'm undertaking: remaking a curta.
The genesis of this projet goes back a little. During the lockdown, I've discovered the curta via a youtube video (https://www.youtube.com/watch?v=loI1Kwed8Pk)

A while later, I've made a tellurion (astronomic contraption that models positions of Sun, Earth and Moon).
https://www.youtube.com/watch?v=tHdg_emv9bs
https://drive.proton.me/urls/TZ1V4R16ZG#g7BRQ7PPiLVf

After making this contraption, I've decided to start making a curta. At first glance, it seems extremely complicated, due to limited mechanical plays, clearances for oil films...

I think this is doable (whithout questions of profit or time), because of the exceptionnal conception : each part is not so complicated. I think this conception was driven by the need to manufacture in high quantity, whithout numerical controlled machines.

The goal of this project is to make a fully fonctionnal Curta Type 1 Rev 2, 1:1 scale. I'm using the original drawings, and I try to buy less tools as possible (I'm making my own special profile mills for gears).

https://drive.proton.me/urls/SB7YSGAQ0C#kcmVdO47eQIq
https://drive.proton.me/urls/X0C3ZZGXZW#xA09qFIgmE0t

I'm currently working on the different gears :

-Counters sliding gears (10038):
https://drive.proton.me/urls/Y3787SAJSG#8pVBM7FVFdaA
These are made out of .5mm sheet metal, then mounted on brass hub (10017, 10020 or 10032)

-Frontal counter gears (10052):
https://drive.proton.me/urls/42XP9E5F10#QZmRcWRIpsvt
https://drive.proton.me/urls/7P567BTBQW#xakU6BPWJB0q

-Counters rollers (10045):
https://drive.proton.me/urls/WSQZHMMRSW#fpXsFju4ZocH
For those parts, I'm planning to use shrink fit workholding fixture to machine the gear.

This project is progressing slowly, as I don't have much time to devote in it (studies etc...).

Let me know if you want regular updates or a deeper view of the machining processes.

One last word: the goal is not to have a 100% conform replica. I'm adjusting the original conception to the available materials, for example the tolerances are varying from the original. I'm also planning to add some interesting features, such as the Silent Curta spring, that weren't implemented on Type 1 Curtas.

Have a nice day,

Thomas.


Last edited by thomasmanegiste on Fri Jul 25, 2025 7:03 pm; edited 2 times in total
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murff



Joined: 27 Oct 2009
Posts: 602
Location: Switzerland

PostPosted: Wed Jul 23, 2025 3:07 pm    Post subject: Reply with quote

What an exciting project!

Which variant do you want to build? I hope an all-metal version... should it succeed -
do you want to produce a small series? I would like to preorder serial number 0002!

How do I get access to the documents? Do I need an account?
(update - I just created an account... interesting pictures!)

I would love to get regular updates on your work!



I wish you good luck and much success!
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Last edited by murff on Wed Jul 23, 2025 7:21 pm; edited 1 time in total
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Kmcqueen



Joined: 14 Apr 2023
Posts: 35
Location: Portland OR, USA

PostPosted: Wed Jul 23, 2025 5:10 pm    Post subject: Reply with quote

I would be interested also - Let me know what to do get access to your photos. I've been trying to picture the process for cutting that spiral groove into the setting shaft for years (without using CNC). I'll be curious to see how you pull that off.
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thomasmanegiste



Joined: 03 Mar 2025
Posts: 4
Location: France

PostPosted: Fri Jul 25, 2025 9:24 am    Post subject: Reply with quote

Hello everyone !

Quote:

Which variant do you want to build? I hope an all-metal version... should it succeed -
do you want to produce a small series? I would like to preorder serial number 0002!


I'm buiding two versions: one all metal, and one with an acrylic outside to see the guts.

I would like to build a serie of curtas, but there are several problems :
-Price : because I can't produce in big quantities, the price will be extremely high. I might sell whithout profit, just for fun, but it will probabely be a thousand at least.

-Technical industrialisation difficuties : to be able to produce several machines, I need to invest in CNC machines (swiss turning center, 3 axis mill), and to rethink my whole process to be more effective.

Depending on how many people want one, I might explore possibilities of serial production. If not, I might make one more for you Very Happy

Quote:
I've been trying to picture the process for cutting that spiral groove into the setting shaft for years (without using CNC). I'll be curious to see how you pull that off.


The principle is to link a linear move (X), with a rotary move (using a rotary table). It might be a little headache, as I don't have a universal rotary table, but it is still possible with a few gears and modifications of my conventionnal mill.

https://youtu.be/uaJsgsLkwQg Example for manufacturing a counterboring mill.

Quote:
Let me know what to do get access to your photos

I don't know why you can't have access to those. Do you mean you can't open the links in my first post?

Let's try this:

[img] https://drive.proton.me/urls/PDTXGCC7MW#BaQEmzgNdeQH [/img]

Tell me if you can see this one. If not, can someone explain me how I should put images? I'm using the img and /img tags.

Have a good day!
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murff



Joined: 27 Oct 2009
Posts: 602
Location: Switzerland

PostPosted: Fri Jul 25, 2025 10:33 am    Post subject: Reply with quote

thomasmanegiste wrote:
Hello everyone !

Quote:

Which variant do you want to build? I hope an all-metal version... should it succeed -
do you want to produce a small series? I would like to preorder serial number 0002!


I'm buiding two versions: one all metal, and one with an acrylic outside to see the guts.

I would like to build a serie of curtas, but there are several problems :
-Price : because I can't produce in big quantities, the price will be extremely high. I might sell whithout profit, just for fun, but it will probabely be a thousand at least.

-Technical industrialisation difficuties : to be able to produce several machines, I need to invest in CNC machines (swiss turning center, 3 axis mill), and to rethink my whole process to be more effective.

Depending on how many people want one, I might explore possibilities of serial production. If not, I might make one more for you Very Happy




OK - I'm there! The early bird price is right Cool

An acrylic case for the Curta series would be cool!
I'm sure a lot of people would be interested in that...

... the historical model:
https://digital.deutsches-museum.de/de/digital-catalogue/collection-object/78037/

PS: The image tags work perfectly - you need to make sure the image source is freely accessible
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thomasmanegiste



Joined: 03 Mar 2025
Posts: 4
Location: France

PostPosted: Fri Jul 25, 2025 12:37 pm    Post subject: Reply with quote

@Kmcqueen
I changed the way I put pictures in my posts. Let me know if it's working for you.
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murff



Joined: 27 Oct 2009
Posts: 602
Location: Switzerland

PostPosted: Fri Jul 25, 2025 1:02 pm    Post subject: Reply with quote

no . . .

between the two Img tages must be the url to a picture file

like this:
https://curta.li/pict/04_werbung/42_innova11.jpg



so you need an image host (or you have your own server...)
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Kmcqueen



Joined: 14 Apr 2023
Posts: 35
Location: Portland OR, USA

PostPosted: Mon Jul 28, 2025 3:29 pm    Post subject: Reply with quote

The new links work for me! Thanks! Also thanks for the machining video - makes complete sense now. I had originally looked at the grooves under magnification and though maybe they were made on a shaper.....but couldn't picture how to get the spiral twist.
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thomasmanegiste



Joined: 03 Mar 2025
Posts: 4
Location: France

PostPosted: Fri Aug 01, 2025 1:53 pm    Post subject: Reply with quote

Hello everyone,
Since the links are working now, I will resume posting. I know that the images should appear immediately, but the storage solution I use gives a link that doesn't end with .jpg or .png, so BBCode doesn't load the image. I'm working on a fix for that problem (making my website to load those images).

Manufacturing of machine's frame:

The frame is made of five parts:
Top body (10011), lower body (10077) and three fastening columns (10064).

Upper body:

https://drive.proton.me/urls/C6CMN8Z2CC#1isjCX37VZMK
https://drive.proton.me/urls/V48GDSH9H0#o16Azw5hV5wC

The first OP is done on a DMG vertical 3 axis mill (no it's not mine, unfortunately).

https://drive.proton.me/urls/MY0JXY2R9M#J66u6bCTgI0M

I've only milled one of the radial slots (machining time was waaay too long, 1mm endmill, 0,002 mm/Z). This slot will be used to trim the part for OP 30.
The frontal groves are machined with a 3mm endmill, with a ramping strategy.

Little tip for Mastercam users:

When using a contour ramping strategy with circular moves, don't forget to untick the option "linearize helixes". Otherwise you will machine a wonderful polyhedra instead of a cylinder.

https://drive.proton.me/urls/CNC7PZEZS0#QZlAFXcYNIiy

The reason lies in the Gcode analysis:

Whithout this option, the gcode will look like this (using Siemens):

G2 X4 Y0 Z-1
G2 X-4 Y0 Z-2

Each line programms one half turn of an helix (180°), while slowly going down.

With this option ticked, the helix will be created as a sum of small discreet moves.

Anyway.

The lower portion is machines with two OP : one lathing OP (unfortunately I didn't take pictures), to machine the Ø33 bore, the part being held with a collet chuck gripping on the Ø8g6.

Lastly, one drilling OP.
The part is trimmed using gage blocks, slid in the radial slot.

https://drive.proton.me/urls/T2CG07E5Q8#DBdiGUYnvjah

I still have to machine the rest of the radial slots.

Lower body:

[url[https://drive.proton.me/urls/03D02BB2BC#bUdIUDdUNNmt[/url]

This part is machined in two lathing OP, and a looong drilling one.

https://drive.proton.me/urls/TCQJK015SM#QbGW1vZAx3ye
https://drive.proton.me/urls/B4TH1XGGTR#WaERKb9RfaYo

This part is not a big challenge, you just have to stay focused while drilling the holes.

Fastening columns :

https://drive.proton.me/urls/DZ89F9ESS4#kET05uREBtsz

At first glance, this part seems easy. Until you realize that the parts must be drawn according to the small table at the bottom right, meaning that for a single production run, a batch of three parts must be within the same hundredth of a tolerance on the length 36.75.

I have defined the following machining protocol (I do not have a spindle stop):
-Machining of the first end
-Turning over and rough cutting to length
-Disassembly and measurement

Then, I machine it to length using an industrial camera to rezero the lathe on the machined end face.

https://drive.proton.me/urls/3QETH97SWR#N9kfhKqi8u7v

Lastly, a bit of threading.

https://drive.proton.me/urls/H2D1QMMXC0#9CpjOyC6psCA

That's it!


Last edited by thomasmanegiste on Fri Aug 01, 2025 7:29 pm; edited 1 time in total
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murff



Joined: 27 Oct 2009
Posts: 602
Location: Switzerland

PostPosted: Fri Aug 01, 2025 4:06 pm    Post subject: Reply with quote

Thanks for the update... You seem to be really getting started!

A question about the materials - you don't seem to always use the same metals - it certainly doesn't matter for the
support columne - but I've read that Herzstark paid close attention to the choice of metals used, which is one reason why
the Curta is so durable.

I'm looking forward to seeing your step drum... that was a tough nut to crack for Herzstark!


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