Online Involute Spur Gear Builder – Part 2

UPDATE: This post refers to an old version. For information about version 2 see this post.

Before you read on, please make sure that you have seen part 1 which introduces my Online Involute Spur Gear Builder. This second part addresses DXF export and compares the generated tooth profiles with the output from a commonly used OpenScad script.

DXF Export

Unfortunately there are many variants of the DXF format and not every tool is capable of importing the dxf output generated by the tool. Here are a few pointers:

  • Inkscape: Inkscape is a free, open source vector graphics tool that can import the generated dxf output without any issues. Inkscape’s native format is svg but it also supports many other output formats that are useful when dealing with other tools.
  • Illustrator and VectorWorks do not seem to recognize the generated output. Lael and Jeroen Donker reported workarounds (thank you, both!):
    • Lael: Just an update for anyone else trying to use illustrator or having issues importing into drawing programs. I downloaded Dassault draftsight, opened the dxf generated by this generator, then saved it as 2009, 2010 and 2013 dxf. 2009 and 2010 opened fine in illustrator.
    • Jeroen Donker: I found that the dxf output file can be opened in Inkscape (freeware on all platforms) and then saved in any vector format (I use eps) Opening the file in Adobe Illustrator is an easy next step.

Generated Output Comparison

It is interesting to compare the generated output with that of other tools. In particular this makes it quite easy to see when the undercuts become relevant. For the following I used Leemon Baird’s featured Public Domain Involute Parameterized Gears for OpenScad. Upfront I want to clearly state that this comparison by no means is intended to diminish Leemon Baird’s code. Like many other tools it simply does not cater for undercuts which in most real-world scenarios can be ignored. If undercuts are not an issue Leemon Baird’s tool is a perfect choice.

For the comparison I chose a pressure angle of 20°, 8 mm circular pitch, no clearance, and no backlash. For reference here is the scad file with the configuration for the 6 tooth gear and the resulting dxf file generated by Leemon Baird’s script.

The images below (excerpts from the svg file InvoluteGearComparison.svg) show the tooth profiles for tooth count 40, 20, 10, and 6. The thicker black background lines represent the output generated by Leemon Baird’s code. The thinner red lines in the foreground are the tooth profiles generated by my online generator:


As expected the two profiles match almost exactly for large tooth counts. It is interesting to see that even for a tooth count of 20 there is a slight undercut visible. I expect in real live this would not matter since it is compensated for by a non-zero backlash.

12 thoughts on “Online Involute Spur Gear Builder – Part 2”

  1. Hi Dr Rainer.

    I am trying to make a rack and pinion gear for fun….I cant seem to be able to do this.

    I have gone through your instructions, but it keeps giving me an error.

    What am I doing wrong…..I am using a mac?

    Kindest regards

    Tony Watts

  2. Hi Rainer,

    I just wanted to say that I’m really glad to have found your involute gear builder. It is the best I have ever seen. I’m on Mac, and it’s the only thing I’ve found to work on OS X.

    It would be great to chat with you if you have some time!

    – Noel .oO(

    P.S. Cool blog!

  3. Hi Dr. Rainer Hessmer
    Thanks for that very fine tool. Unfortunately in AutoCad 2017 (and 2014) I can not open the dxf file, it says “Tabellenmarken fehlen auf Zeile 32, ungültige oder unvollständige DXF Eingabe ,, Zeichnung abgebrochen”
    Do you have a workaround?
    Hubert K.

  4. By Ahmed( an M.Sc student)
    Dear Dr. Rainer Hessme

    I am very very grateful for all the hard work that you did for this amazing tool, However, I will be really grateful if you could answer my question below:

    Dr, what firstly about the amount of root fillet the online program does not ask for the amount of the radius of the root fillet.
    secondly does the root filet is the circular or trochoidal type,
    finally, does the program take into account the critical correction factor to prevent addendum dedendum interfering.

  5. Hello Rainer,

    I really like your tool. Everything works fine, I just can´t download the dxf. It generates but doesn´t download.

    Thank you


  6. Found this wonderful tool online. Thanks for putting it together, very flexible.

    I think there is a bug in the internal gear treatment of clearance, however. With clearance non zero, the internal gear inner radius is increased (tooth is less tall), and the outer radius is unchanged from ideal (no extra depth in valleys). When creating a gears set with one pinion and one internal gear with a non zero clearance specified, you get this effect:

    Pinion (regular spur gear)
    addendum = standard
    dedendum = standard + clearance (deeper)

    Gear (internal spur gear)
    addendum = standard – clearance (shorter tooth height)
    dedendum = standard

    This results in line to line interference of pinion addendum with internal gear dedendum, and twice the clearance between pinion dedendum and internal gear addendum.

    Looking at the code, I think the problem is the clearance is added to the innerRadius (makes shorter teeth) but not to outerRadius (leaves valleys alone), which seems backwards. For there to be clearance, the internal gear outer radius needs to be increased given the pinion addendum is not changed.

    Maybe I misunderstand how this is supposed to be used, but when I create a gear set this way, I have no actual clearance, which I think is missing the point. If I could upload an image, I could show you this on a CAD drawing.

    Thanks for any help.

    Mike Ciholas

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