Negative extrusion error

[etfrench]

This GT2-2mm pulley extrudes properly when the distance is positive and fails when the distance is negative.  The pulley was created in Gearotic, saved as an stl, then imported into Fusion 360.  After creating a Mesh section sketch, the Closed Spline curve type was used.

[wmhazzard]

There does seem a few problems with section sketch, see this thread. https://forums.autodesk.com/t5/fusion-360-support/impossible-to-create-fit-curves-to-mesh-section/m-...

There does seem to be a problem with the ellipse. 

[Beyondforce]

Hi @etfrench ,

Will you please attach the file, I would like to test it.

Cheers / Ben.

[etfrench]

I thought it was attached, but doesn't appear so now.  Here it is.

[Beyondforce]

There is definitely something wrong is going on there with the extrude. Also, when you zoom in, the borderline looks like this, WHY? Why the line is not smooth? And why there are two lines?

[etfrench]

The orange line is the mesh section.  The output from Gearotic is in short lines instead of arcs.  It works fine for 3d printing, but when I use the milling machine, I redraw it with arcs.

[etfrench]

The curvature display is rather interesting 😀

[laughingcreek]

What your seeing is a display artifact, not the model itself.  if you right click the body in the browser and change the display detail control to fixed/high, it looks correct.

I found it interesting that there where no edge/tangent lines in the resulting body, so I took a closer look there also.  the profile isn't made up of a bunch of short lines (also a display artifact), but is one single continuous fit point spline.  you can observe this to be true by right clicking on the line and selecting "show control frame".  you have your self a very heavy model as a result of that one outline.  personally, I would model this properly in fusion.  the model would behave better (because it would be much lighter), and all the geometry would be correct (right now you have variations from tooth to tooth)

[etfrench]

@laughingcreek Thanks.  That's another menu item I've never had the occasion to use 😀  Yes, the wonky profile is a spline created by the mesh tools.  The original stl model from Gearotic uses short lines.  The short line model works fine for 3d printing (FDM not SLA) as the variances are in the micron range.  I will spend the time to make a proper model if I'm milling a pulley.  The GT2 tooth form is simply 4 arcs, so it's not hard to do.