Internal ring gears

[mthuff]

I need to model a normal gear running within a ring, the internal face of which is geared. I can find no means of drawing the latter within the scripts that came with Fusion 360. Is there a script extant for this, and if so, where please?

[Mike.Grau]

Hi @mthuff,

Thank you for asking about that.

You can use this open source tool wsith to generate internal spur gears

and export your gears as *.dxf. Then insert your *.dxf into Fusion 360.

The engineering way would be to start with sketch´s and use the parametric to control the entities.

Once this is set up, you can use it for multiple gears.

I hope this helps. 

Thank you,

[mthuff]

Mike, Thanks - but I can't see the name or link to the "open source tool" you allude to! Probably my error - I don't use forums with much frequency...

[Mike.Grau · Accepted solution]

Hi @mthuff,

Thanks for your asking.

I´m sorry for my bad wording. 
I haven´t attached any link to an open source gear generator but by googling it

I have been able to find a couple one´s who generate gears and allow the export into *.dxf.

I definitively recommend to start from the bottom up and get familiar with gear equations.

You will modify your parameters multiple times during the design process.

Making it parametric in the first shot keeps you from getting frustrated later 😉

Thank you,

[canoe]

I am not sure if this would help but you could create the gear as a normal gear and then Boolean it from the ring. Kind of like using the gear as a cookie cutter.

[etfrench]

That won't work at all   A simple search will return quite a few tutorials on how to design planetary gears in Fusion 360.

[GalindoFinn]

Hi, I have been trying exactly what you suggest with http://hessmer.org/gears/InvoluteSpurGearBuilder.html

However the dxf file generated by this program will not import into F360. Is there any reason for this please?

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@Mike.Grauwrote:

Hi @mthuff,

Thank you for asking about that.

You can use this open source tool wsith to generate internal spur gears

and export your gears as *.dxf. Then insert your *.dxf into Fusion 360.

The engineering way would be to start with sketch´s and use the parametric to control the entities.

Once this is set up, you can use it for multiple gears.

I hope this helps. 

Thank you,

---

[HughesTooling]

Not sure why Fusion doesn't like that DXF but you could use QCad to save as a newer version, see attached.

Note, you will not get smooth surfaces from your file as it's made up from about 800 line segments, no arc or splines at all.

Mark

[GalindoFinn]

Thanks will try QCAD

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@HughesToolingwrote:

Not sure why Fusion doesn't like that DXF but you could use QCad to save as a newer version, see attached.

Note, you will not get smooth surfaces from your file as it's made up from about 800 line segments, no arc or splines at all.

Mark

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[mike46YZU]

Hi,

I made an add-in for F360 for generating internal gears. You can download it here:

https://baxedm.com/python-fusion-360-internal-gear-generator/

I wanted to model an internal gear with a parametric model, but this wont work with involute curves as F360 cannot but constraints on splines in between spline points without throwing an error after the parameters in the model change. I also tried several online DXF generators, which all gave bad geometries or approximated the involutes with straight line segments, resulting is super complex parts that even made my F360 chrash. I tried everything, and eventually saw no other solution but to write my own add-in.

So, no more frustrations when you want to make a internal gear, just use my add-in, enjoy!

BTW, if you want to make internal gears in your home shop, look around on the baxedm site, you'll find lots of info on how to make your very own wire EDM machine.

[HughesTooling]

@mike46YZU  Thanks for doing the script. I have a couple of suggestions. Did you look at the gear script that comes with Fusion?  Like the add-in that comes with Fusion, to get better performance draw 1 tooth then pattern the extrusion. Create the gear in a new component to make it easier to build an assembly, create components from bodies should be avoided.

Don't know if you can just cannibalize the gear script that comes with Fusion. Might be worth doing a check the OD is big enough, just tried to make a gear and got a blank cylinder, took a few second to realise I forgot to set the OD.

Thanks Mark

[MRWakefield]

I thought I'd give this a try using the specifications of a gear I had to model in the past for a scavenge pump (3.0 MOD, 23 tooth 30°PA). Unfortunately there's something not quite right (see attached screenshot). As you can see the flanks of the gear teeth seem to cross each other and produce a triangular cut (you'll see it in the screenshot). I've not done any measuring of the model so I can't say whether the geometry goes too far (diameter-wise) or whether the involute form is a bit off. Anyway, I thought I'd be helpful bring it to your attention.

[mike46YZU]

There is definitely some room for improvement of my add-in. Speeding it up and adding input validation would be the next logical steps. I might add this in the future, but I'm very short on time. It aint pretty, but it works for what I need it to do at this moment.

[mike46YZU]

When writing the script, I googled around to find the correct dimensions of the different construction circles. Which I found were:

pitch_circle_diameter = (teeth*module)
tip_circle_diameter = pitch_circle_diameter - 2*module
root_circle_diameter = pitch_circle_diameter + 2.5*module
base_circle_diameter=teeth*module*cos(pressureangle*pi/180)

These generic geometric rules worked well for the gears that I want to make, which all have at least 70 teeth or so (planetary gear annulus). I noticed that for a smaller number of teeth the geometric rules should probably be different, larger pressure angles also affect this. However I've only implemented the basic rules given above. The add-in should have input validation to warn for this. Making a single add-in that can cope with all ranges of all parameters is a lot harder.

[MRWakefield]

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@mike46YZU wrote:

When writing the script, I googled around to find the correct dimensions of the different construction circles. Which I found were:

pitch_circle_diameter = (teeth*module)
tip_circle_diameter = pitch_circle_diameter - 2*module
root_circle_diameter = pitch_circle_diameter + 2.5*module
base_circle_diameter=teeth*module*cos(pressureangle*pi/180)

These generic geometric rules worked well for the gears that I want to make, which all have at least 70 teeth or so (planetary gear annulus). I noticed that for a smaller number of teeth the geometric rules should probably be different, larger pressure angles also affect this. However I've only implemented the basic rules given above. The add-in should have input validation to warn for this. Making a single add-in that can cope with all ranges of all parameters is a lot harder.

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Yes, gears are definitely a specialist subject. I've had to write code to produce involute spur gears but as in your case it's only been for the most basic profiles. Once you have to consider more extreme examples and you have to start shifting profiles and accounting for interference etc. it certainly makes it more difficult, unless you're a gearing expert that is, which I definitely am not!

[chrisplyler]

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@canoe wrote:

I am not sure if this would help but you could create the gear as a normal gear and then Boolean it from the ring. Kind of like using the gear as a cookie cutter.

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An internal gear that will properly engage around an external gear does NOT have the same geometry as something made per your suggestion.

[Anonymous]

Dear Mr. Mike Grau,

I am facing issue with how to engage the gear tooth. You know, when I rotate the gear tooth, it crosses each other. I've attached the screenshot as well to elucidate. I hope you will guide me how to fix the problem. 

Best Regards.

[TheCADWhisperer]

You have replied to a thread marked as solved and you problem is different than the original issue discussed in this thread.

Attach your file here.

Temporarily suppress the joint. Line up the teeth and then unsuppress the joint.

[Anonymous]

Oh, sorry for that! I am attaching the file as it the prescribed solution is not fixing the problem.

Kind Regards.