Cycloidal Gear Builder


As part of my research into wooden clock making I learned about cycloidal gears and was surprised that I couldn’t find a free or open source tool for generating templates for this kind of gear. Free options do exist for the more common convolute gears (e.g., I did however find Hugh Sparks’ excellent write-up on cycloidal gears and the associated JavaScript based calculator. The calculations reflect the British Standard 978, Part 2.

New Open Source Gear Builder Utility

UPDATE: The information below is still valid but in the meantime I created an Online Cycloidal Gear Builder which is easier to use and does not have any install requirements. You will probably want to use it instead of the older desktop app. More info here.

Back to the original blog post …

To remedy the lack of free and open source tools for cycloidal gears I created a .Net 3.5 WinForm application that generates SVG (Scalable Vector Graphics) output for meshing gears. Under the hood the application uses the formulas as described by Hugh Sparks. Here is a screenshot of the application:


The middle left part is the input section. Based on the inputs a number of output values are calculated and displayed in the left section. For an explanation of the term module and the various output values please see Hugh Sparks’ web page. In order to generate an SVG graphic for the specific gears click on the ‘Generate & save SVG‘ button. By default the output is saved as a file called CycloidalGear.svg in the folder that the program is executed from. Another output file can be specified by clicking on the ‘…’ button. Note that an existing file with the same name will be overwritten! This is on purpose since it makes it fairly simple to use a browser to display the graphical output. The typical usage pattern is as follows:

  • Specify the input parameters
  • Click on the Generate & save SVG button
  • Open the generated svg file in a modern browser that has SVG support (Firefox or Chrome work very well). You should get something like this:
  • Now you can repeatedly change parameters and regenerate the svg output. Each time after clicking theGenerate & save SVG button, switch to the browser and refresh its output by clicking F5.

The generated output can be further enhanced by using a vector graphics editor that supports SVG. One attractive option is Inkscape, an open source, multi-platform vector graphics editor that directly operates on the SVG file format.

The British Standard 978, Part 2 results in quite a bit of room between the trough of one gear and the apex of the other. It is possible to override the default behavior by checking the box ‘Custom Slop‘ and specifying the desired slop in mm:


The figure below shows meshing teeth with default slop (left) and custom 0.3 mm slop (right). Notice that on the right the dedendum circle of one gear almost touches the addendum of the other. The distance is the specified 0.3 mm.



The application is implemented in C# and requires Windows with .Net 3.5 installed. Most Windows PCs have this version of the .Net framework already installed. If it is missing it can be downloaded from here. To install Gear Builder please follow these steps:

The application is self contained and does not depend on the registry, etc. As a result it can be simply uninstalled by deleting the extracted files.

Source Code

The application is coded in C# using Visual Studio 2010. The source code can be accessed from the associated Google code project site, specifically For the generation of the svg output I use a slightly enhanced version of Ben Peterson’s SVG framework library.


The application itself, as well as the associated source code, are covered by the permissive MIT license. The application leverages Hugh Sparkes’ formulas as well as Ben Peterson’ SVG library. Both do not come with specific licenses.

27 thoughts on “Cycloidal Gear Builder”

  1. Hey Doc!!
    I am a salesman/ eng/Purdue looking for some info. I have a customer using Nabtesco cyclodail boxes. 1 arc/min blash. back n the day I reped Dojen now Dojen/Onvio Mass. I think Sumotoma
    maybe Siemans makes these things ?? I work on commision only and love the freedom. I bring these
    these apps to potential manufactures. I have been looking for other MFGs ?? Can u give me some leads as 2 who else makes them. Thx

  2. great work.. i was wondering if i might be able to get some help am using emg30 with the MD25 through Arduino but i seem to be getting a communication board error..

    have you come cross this?


  3. Nice one glad to see it ……..

    Actually I want to know more about this cycloidal gear , and its profile and also about its manufacturing how it is made.

    And some more knowledge about gears.

    So sir I am requesting you to please help me in this.


  4. FANTASTIC! I’ve been waiting for some genius to make an open source cycloidal gear generator! And such a great interface, simple, Perfect!
    Thank you for sharing your brilliance. Now all we need is escapement wheels…!
    All the best, John

  5. Rainer,

    An excellent utilty – thanks.

    Is there any chance of a DXF output as well as the SVG as it would be nice to be able to see the output in AutoCad?


  6. Phil, I don’t have plans to add support for DXF but you might be able to get the desired output from within Inkscape after installing this add-in: Inkscape DXF Export Extension. I have not tried it myself, though.

  7. Thanks Rainer. I have tried Inkscape but when I try to open the DXF in Autocad 2005 I get very strange results which make it unusable. Cheers. Phil.

  8. I’m building the Clock from ScrollSaw woodworking magazine.Summer 2013 issue 51. On the article that covers ratchet mechanism, how is the weight cord attached and how are the weight attached to the ratchet assembly. Any info would help.


  9. Hi I’m working on a cutting system for wooden clock gears and came accross your open gear planner

    I have windows 8 install and could not open the exe. files. your help would be appreciated

  10. Hi Zeldar,
    The gear builder depends on the .Net 3.5 framework which, by default, is not installed on Windows 8. You can find instructions for how to enable .Net 3.5 here: Installing the .NET Framework 3.5 on Windows 8 or 8.1

    1. Awesome gear generator, thanks for sharing!
      I am experimenting designing cycloidal gears with FreeCAD and did a video on YouTube and want to make sure it is OK to share a link to your gear generator
      Best Regards

        1. Here is the link to the video on Youtube

          FreeCad allows all parameters to be fully customizable and the animation helps in seeing the meshing
          I am not an engineer, but 40 years of experience as an AG technician help in having a feel for what should work
          And indeed my latest clock with a Grasshopper escapement works nicely
          I will be happy to share how to get the geometry, CAD program do make it easy

          Also links of interest about cycloid gears:
          Owner allowed me to share the links, so here they are
          Meshing of cycloidal gears

          Geometry of cycloidal gears:

  11. Thanks for making this program available. Unfortunately I was unable to download the source via SVN, the server gives the error that it can’t find it.

    Any advice on how I might proceed from your program and Hugh Sparks’ work to getting the tooth profiles in rectangular or polar co-ordinates?


  12. Dear Dr.

    I have a small cnc lathe that is controlled by sending X,Y coordinates. Is there any way I can use your program or an equation from it to calculate moves to make a gear cutter. It seems like the tops of clock teeth are derived from circles and the base is trapedoidal?
    Tthis would be easier than printing the teeth and measuring the paper!

    Thanks for your program and attached article…


    R. Wood

  13. Fascinating information. Look forward to playing around with this and helping people understand the concept of cycloidal gears to customers, and lay people.

  14. Dear Dr. Hessmer

    It looks like you may not be monitoring this blog any more, but in case you happen to see this, the “cycloidal gear builder” is a really nice program, thank you.

    Unfortunately the DXF output I have downloaded from is failing when imported into AutoCAD 2013.

    I will try and edit the DXF file to make it work; the important parts obviously are the polyline entities.

  15. Very interesting details you have observed , regards for putting up. “I don’t know what you could say about a day in which you have seen four beautiful sunsets.” by John Glenn.

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