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Spur Gear Error

Message 1 of 6
447 Views, 5 Replies

Spur Gear Error

Hi, I am creating a spur gear train and have a 8 toothed gear, when I try to create it I get the following error 'drawgear failed : 5 : some input argument is invalid.'.




Can anyone help please?


Message 2 of 6
in reply to: segittins

Without more study, my 1st thought (or question) is the actual size of the gear something that 8 teeth will fit on?

What I mean is can the blank size you set "fit" 8 teeth? There is a correlation between the pitch and circumference.

I have made some gears for my lathe, but I had a known gear to start with so size and teeth were known.

Message 3 of 6
in reply to: 2herds


Thanks for your response.

Managed to figure it out, for some reason the spur gear app wasn't happy with the 'backlash' setting at 0.5, setting it to 0.3 generated the gear.

Message 4 of 6
in reply to: segittins

Both of these are a bit big for the module size. Normally something around 10% of the module should be used.


EDIT. 10% for the root radius is about right but I guess backlash will depend on how you manufacture the gear. I use about 0.01mm on gears I wire erode, for 3d printing you'd need to experiment. One thing to be aware of, gears with less than about 16 teeth need undercuts in the root to stop interference so for these gears the add in does not create good gears.



Mark Hughes
Owner, Hughes Tooling
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Message 5 of 6
in reply to: HughesTooling

Thanks for taking the time to reply.


I managed to find out what was wrong and the backlash value was too high, reducing this to 0.3 fixed the error.


Thanks again. :-))

Message 6 of 6
in reply to: segittins

This error is caused by a code bug in c:/Program Files/Autodesk/webdeploy/production/540c9578410bc15ff261605667cfced82aa9ac6d/Python/AddInSamples/SpurGear/commands/spurGearCreate/


If you speak python, you might be able to fix the bug yourself.   Specifically, when making small gears, sometimes the code can make an arc which is too 'straight' - ie. to the numerical precision fusion360 uses, it appears to be a straight line.


The fix is simple - just make it a straight line!   I changed this line of code:


toothSketch.sketchCurves.sketchArcs.addByThreePoints(spline1.endSketchPoint, midPoint, spline2.endSketchPoint)

into this line of code:


toothSketch.sketchCurves.sketchLines.addByTwoPoints(spline1.endSketchPoint, spline2.endSketchPoint)

And suddenly the whole thing works again!   Note that if you get the error, inspecting the partially completed gear tells you which part it failed at, which gives clues where to adjust the code.


Hopefully the fusion 360 devs can incorporate that fix into the next version!

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