Kotta Calculator Type I

The CURTA calculator is a purely mechanical portable calculator invented and produced in the 1950s

Possessing intricate structural design and unique mechanical charm, it is an important milestone in human mechanical manufacturing technology

This project is a 3x scale model of the CURTA calculator Type 1, designed specifically for FDM printing, modeled according to mechanical design drawings, and optimized for FDM printing

Model validation material: PETG/PETG-CF

Finished size (approximate): 300*150*150mm

Other configurations include an uploaded mold for easy spring and torsion spring production, optional to print

Notes:

Hardware parts are required, refer to the assembly instructions and BOM for details

Due to different material shrinkage rates, please first cut and print the parts with holes for shaft mating to verify tolerance and determine appropriate hole compensation

Printing instructions:

1、The model requires strong hands-on ability and some basic mechanical knowledge

2、For B2/C1-1/C1-2 plates, -CF type high-strength material is recommended (requires the use of high-wear-resistant nozzles such as hardened steel)

3、Some printed parts have sacrificial supports for easier printing, which need to be removed

4、All multi-color print parts have grooves, which can be brush-painted after single-color printing (the effect is slightly poorer due to the presence of layer lines)

Special thanks:

Marcus Wu's work on the Thingiverse website for the help it provided in understanding the internal structure

Update v1.2 (2024/11/06):

1、Some players reported difficulty removing supports for A1-1/A2 plates, A1-1 has been adjusted to tree-organic tree supports, and A2 has been split into parts for printing

Update v1.3 (2024/11/12):

1、For the hole-shaft mating parts, while ensuring normal transmission, the holes have been uniformly increased by 0.1mm for assembly tolerance

2、Corrected a parameter error in the nut installation part of the [F1] component (original diameter 4.2mm, modified to 3.8mm) to better fit M4 nut installation This part can be reprinted or the nut installation area of the already printed part can be cut and polished

Update v1.5 (2024/11/18):

1、The [B2-1] long shaft has been split into parts and placed for XY plane printing to increase torsional resistance If there are strength issues, it can be reprinted

2、To accommodate the changes to [B2-1], the internal hexagonal connection of [I1-1] has been modified If the long shaft split parts are reprinted, [I1-1] needs to be reprinted

Update v1.7 (2024/11/26):

1、Enhanced and repaired the issue of low strength in the [H3] cylindrical push rod If the push rod is prone to breaking, this plate can be reprinted

Update v1.8 (2025/04/20):

1、Corrected some support issues in Bambu Studio 2.0 software, optimized [E1] support settings for easier removal

2、Adjusted some details of [B2-2] (no need to reprint as it does not affect assembly)

3、Removed some auxiliary supports from [J2] and used slower outer wall printing to achieve the same appearance

Update v1.9 (2026/07/07):

1、Modified an interference issue caused by strengthening the connection point of the [H3] component

Problem description: If the register digit is 2, moving the upper register part is required for carry-over multiplication or division calculations After shifting, the number wheel will interfere with the step carry rod, leading to stepping errors, as shown in the figure below

Thanks to Bilibili user UID3546580554615417 for discovering and reporting the issue

Assembly instructions: