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Using Inkscape, I want to draw a inner gear.

In Inkscape, there is useful extension to draw a gear. I've used that extension to draw gear with tooths pointing to outside of a circle, like so:

enter image description here

but I want to draw a gear with tooths pointing to the center of a circle -- draw a inner gear:

enter image description here

Is there some tool, which will allow me to flip a tooths of outer gear around the circle, so the tooths will point into a middle of a circle? Or, how You would draw such shape?

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  • Can you post a picture of a sample of this gear you want to draw? – jqning Jun 8 '15 at 0:26
  • The involute is the same on both sides of a involute gear (depicted) – joojaa Jun 8 '15 at 6:19
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  • You can just interprete the space between the teeth of an outer gear as teeth of the inner gear and vice versa. This may not be very realistic but may suffice for your needs. For example the following two were generated from the same output of the gear renderer:

    outer and inner gear from the same rendered gear

  • If the above does not satisfy you, the only way I see is something like this:

    1. Create some cocentric circles.
    2. Extensions → modify path → add nodes
    3. Combine everything.
    4. Edit paths by nodes, connect the points as desired and remove the rest. Compare to steps 13–15 of this answer of mine.
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  • Initially I've thought to something similar, but the shape of the teeth of the inner gear is unrealistic (there is no leisure to spin a gear, see also here and here as reference). There is an interesting doc here. – Paolo Gibellini Jun 8 '15 at 9:40
  • @PaoloGibellini Its the same shape its just that the very base needs to be trimmed off. Yeah i have reference i front of me both in physcal form and as full 3d models. – joojaa Jun 8 '15 at 11:07
  • @joojaa The shape of the space between the teeth needs to be different from the shape of a single tooth. – Paolo Gibellini Jun 8 '15 at 15:02
  • @PaoloGibellini its a bit wider and starts at different height but its still essentially the same shape. That is why we use involutes their pair no matter how offset is an involute of the base circle. Differently sized circles come off with diffeently scaled sections of involutes. I didnt say the image depicted here is correct just saying it is essentially correct. For graphics design good enough. If you want the exact shape then lets move over to engibeering.se – joojaa Jun 8 '15 at 15:10
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    @PaoloGibellini anway the formulation for the involute shape can be found here – joojaa Jun 8 '15 at 17:02
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I'm able to create realistically looked image, but I need to draw a series of gears, which will be used in animation and my approach has several drawbacks, which will heavily complicate my quest.

The gears are always meant to be combined with other gears, right? And classical circular gears, if combined, has to have the same shape of involute to work together. So if I want to draw a inner gear with counterpart outer gear, I have to use the same shape of involute for both gears, but on inner gear, the involutes will be flipped towards center of a circle.

  1. We can use Inkscape Extension → Render → Gear to create a perfect classical outer gear easily.
  2. Duplicate that gear and on the duplicate remove all nodes except one involute.
  3. Flip the involute around, create a circle, slightly bigger than original outer gear, and place the involute to inner part of the new circle.
  4. Mark center of the circle, and to this center move the point of rotating of the involute.
  5. Duplicate the involute and while pressing Ctrl rotate duplicate by one step. Because we have the point of rotating in center of circle, the duplicates will move regularly on the circle.
  6. If you are lucky, after few finishing touches, you will end up with inner gear, which could be combined with original outer gear.

enter image description here

But this approach has one big issue. You cannot easily adjust the diameter of gears, because by stretching the gear, you are also changing its involutes.

Is there a way, how to use some oject as a stroke for another object?

Imagine I will have one involute used as a stroke of two circles. I can then change the diameter of the circles without changing its involutes or change the involutes of both circles by simply modifying one underlying involute object.

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  • While most of your answer answers your question, you also ask a new question, which will break our question-and-answer format. If you want to ask about this, you really have to ask a new question. However, take a look at extensions → generate from path → pattern along path first. If this helps you to achieve satisfying results, you can update this answer. Also note that scalability will always be an issue with gears. – Wrzlprmft♦ Jun 9 '15 at 5:51
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I'm a little perplexed by the complexity of the answers that have already been provided. Can you just cut the shape of the gear out of a circle?

  1. Render the gear as normal (this will represent the negative space in the center)
  2. Create a circle (send behind the gear to make things easier to see)
  3. Align the circle and gear
  4. Convert the circle to a path Ctl + Shift + C

  5. Select the gear and ungroup it Ctrl + Shift + G (For some reason, the extension renders the gear and groups it with itself, this prevents you from cutting the path, which is by this step is needed.)

  6. Select the gear, then the circle

  7. Click Path > Difference

This will cut the shape of the gear out of the circle. Is this not what you were trying to accomplish?

Note: If you want to make a gear that will fit this shape, copy the original gear first and set it aside. Change its path to inset (Path > Inset) and it should fit. If you need more control, play around with the stroke width, even using a white stroke.

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  • For a real gear, not really but @Wrzlprmft has exactly the same answer. – joojaa Jul 9 '15 at 12:43

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