Online Involute Spur Gear Builder v2

Version 2.0 of my online involute spur builder is available now: Online Involute Spur Gear Builder v2. It is a complete rewrite of version 1 which was introduced 2014 (part1, part 2).

Version 2 creates higher quality output without ragged edges at higher speed. Like before, undercuts as needed for small tooth counts are correctly handled; clearance, backlash, and profile shift are fully supported.

As an extreme case the image on the left shows a 12 tooth gear meshing with a 5 tooth pinion (tool link). Notice the extent of the undercut. The image on the right (tool link) shows the same gears but this time with profile shift applied. The profile shift considerably strengthens the pinion gear teeth.

Without profile shift Involute gears with undercut and profile shift.

The key differences of v2 compared to v1 are:

  • Modern SVG output
  • Higher quality output (no ragged edges) without excessive segment counts. No more need to fiddle with quality parameters.
  • Significantly faster than v1 at any acceptable quality levels
  • Parameters are automatically injected in the URL; i.e., the URL fully specifies the output and can be shared with others.
  • Corrected internal gear generation (e.g., clearance is properly applied)

In case you are interested in how the gear shapes are created, the first post that introduced version 1 is a good start. Then this pdf document provides more detail about how v2 accomplishes the smooth curves that v1 struggled with. Internal gears are particularly challenging in this regard. Here is just a teaser:

Internal Gear Shape Creation

Cycloidal Gear Builder

Introduction

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., http://woodgears.ca/gear_cutting/template.html). 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:

Application_v1.0_Screenshot

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:
    OutputInFirefox
  • 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:

CustomSlopDefinition

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.

DefaultVsCustomSlop

Install

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 http://code.google.com/p/drh-horology/source/checkout. For the generation of the svg output I use a slightly enhanced version of Ben Peterson’s SVG framework library.

License

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.