How to find central angle of irregularly-shaped object?

[Anonymous]

Disclaimer: I am in the medical field and am doing work in Urology so am working with 3D models of curved penises.

I am trying to find the central angle of curvature of these models but am having trouble finding the best/most precise way of doing so. I tried constructing circles at the base and the tip, duplicating them, then transforming them in order to create axes (as seen below), but this doesn't seem to be very precise and I get different angles every time. Also the lines don't intersect. I also tried creating planes on either side of the shaft, then doing a midplane and trying to construct axes that way but that also didn't work because of the irregular topography. Any ideas? I don't have the most experience with fusion360.

[wmhazzard]

Have you tried using "create mesh section sketch" under the create menu. 

[laughingcreek]

In order to get the 2 legs of your angle to meet at a vertex, they will need to be created on the same plane.  that will be hard to do using axes.

One possible approach would be to move the model so that it is split long wise  by an origin plane (so the cross section at the plane looks like an L).  You can fine tune the plane position by splitting with the plane and then comparing the volumes of the 2 halves (right click body in browser ->properties).

once that is done, place a sketch on that plane and draw your best approximation of the angle with sketch lines.  you can split the 2 halves again with the lines ,and compare the volumes again to further fine tune. 

edit-that last sentence doesn't really make sense. oops

[laughingcreek · Accepted solution]

Here's a screen cast of the process described above.

https://knowledge.autodesk.com/community/screencast/335a3deb-5095-419e-b530-a76bb7a56bce

[Anonymous]

Thanks! So just tried that and get basically an outline of the object at the plane that I set, but how then do I measure the angle? It won't let me construct any lines or anything on that plane. 

[Anonymous]

Thank you so much!

[Anonymous]

Thank you! So when drawing the my best approximation of the angle with sketch lines, the idea is that I want this to be as precise as possible and hopefully be able to be reproducible so if I have multiple people find the angle this way they all get very similar results. I would imagine that sort of approximating where the point of maximal curvature is for the intersection point of the lines as well as approximating where to position the lines can lead to very different angles if done my multiple people for example. So is there a way to make sure the lines that you drew at the end are completely in the center? (maybe something similar to the measuring the two volumes trick that you did)?

[laughingcreek · Accepted solution]

I can't think of a great way to be completely accurate. I would probably place lines by eye ball that are perpendicular across the width and use the center points.  Not mathematically accurate.  but then again, the exact center of the object is going to vary along it's length.  it wouldn't be a straight line.  good enough is relative,  and I imagine there is some artistry involved with what your doing.

A whole different approach might be to create a pipe feature along the lines, and then use the pipe as a visual reference to center everything up.  I can demo that later if your interested.

What do you need to end up with? 2 lines at an angle to each other, or a centered path that might have curves?

Keep in mind that even though eyeballing things isn't really the best approach from a cad perspective, I think it's the best your going to do for this task.  Luckily scale is on your side.  if you can zoom in on an object so it is much bigger than it is in real life on your screen, you can get amazingly close by eyeballing.

[Anonymous]

Thanks! I'm looking to end up with 2 lines at an angle to each other in order to measure angle of curvature, as well as a central path in order to measure length (unless the 2 lines can also accomplish this). I'd love to take a look at the pipe feature as well though! Thank you for the advice.