Object Snap Trouble -> Suggested Improvements

[william.mackinnon]

Hi everyone,

Really enjoying a very steep learning curve in modeling with fusion 360 but I think I need a bit of assistance if possible. My background is not CAD its actually Prosthetics and orthotics so this is a fairly new area for me although I have dabled with sketchbook and inventor in the past.

I am having a bit of trouble with the snap feature not performing as I had hoped it would, perhaps you may be able to point me in the right direction. I have looked over all the videos I can find on the subject but with no luck. I'm sure its my inexperience causing the problem.

I have attached a screenshot of the scanned rectified trans femoral plaster model which I had hoped to model over using the snap feature - the intention of closing the sockets distal end, thickening, adding cutouts, trimming,  adding components and so on. Admittedly I havent thought much beyond this point. The problem I have is the detail around the tuberosity...sorry if you look at the scan you can make out a sort of  feature that curves quite sharply up the wall of the model. No matter how many faces I create this area snapping always creates a web and looses definition or comes up with a t spline error , also the t splines end up as a bit of a mess at the top of the model which I havent figured out how to fix.

I appreciate that the snapping feature may have some limitations but feel this is more likley due to my lack of knowledge in this area. Would you be able to make make any suggestions or have advice on how to go about obtaining a better surface model on a model such as this and how I might also deal with the Socket end?

many thanks in advance and apoligies for the novice question.

Bill macKinnon

National Centre for Prosthetics and Orthotics 

University of Strathclyde

[Anonymous]

Hi Bill, great question. I've found in order to make a very high quality Tspline mesh to near perfectly conform to an imported mesh, it is necessary to first create a Tspline loft that closely follows the imported mesh, before doing a Tspline pull operation. In the following thread is a video describing this process, which would be near identical for your mesh, except that the loft profiles would be closed in shape.

http://forums.autodesk.com/t5/design-and-documentation/foot-insole-modelling/td-p/5715117

Looks like a really interesting application, and let us know if you run into any trouble.

Jesse

[william.mackinnon]

Hi Jesse,

Thanks for the reply, going to have a look at it now.

Also noticed I used the SNAP alot in the OP where it should have been the Pull command - my mistake.

In the meantime I managed to create the model (sort of) using the surface tool / snap to surface and create a fairly rudimentary model then by subdividing the faces while trying keep them to a minimum but where the detail was greatest. I didnt spend a great deal of time on this (didnt think it would work lol) and didnt really think through the patching of the distal end. On one hand it worked fairly well and only required a tweak here and there on the other it has left me scratching my head as to how I edit the trim of the socket -still in at the deep end....

way out of my comfort zone here.

Thanks

[Anonymous]

Wow that looks amazing!  So I'm not exactly sure how you did this, my guess is that you first used, while in the Sculpt environment, the Create > Face tool with Object Snap check-marked?  Then you used Modify > Subdivide, again with Object Snap check-marked.  With the latter, I didn't know until trying it just now that the subdivision with object snap will conform to the imported mesh automatically, and quite well, very cool!

It looks like you then exited out of Sculpt and did a Thicken operation?  Either before or after this operation, you can just use a construction plane, a line in a sketch, etc. as the splitting tool in a Split Body operation to clean that end.  

Thanks for the great new knowledge!

Jesse

[william.mackinnon]

I think you hit the nail on the head with how I managed it. I thought there might be more success if the t splines followed the models shape,contours as hinted at in other videos but the cylinder pull didn't do it even when I adjusted the model as closely as I could, maybe due to the orientation of the horizontal splines...... its obvious that t splines aren't fans of sharp edges..... well so I have discovered.

I may have had a .5mm offset applied as well but don't think this would have made any difference. A few points did require a small adjustment but not much at all.

Added a 6 mm operation just to see if it would work - ran into a few manifold warnings (messy on my part) but managed to clean them up once I found out what that was.

The trimming may be difficult but will study your video closely. I have attached images of the trim for this socket which may be tricky as its not symmetric. Again haven't thought about that as yet lol.

Thanks for your assistance...

Bill

If you have any more thoughts let me know.

[Anonymous · Accepted solution]

Hmm, yeah that looks like quite a complex cut you want to do on the bottom there.  You could do the following method.  When in the Sculpt environment, create a sketch (doesn't matter what plane defined on), be sure 3D sketch is on as shown below (or can in Preferences turn it on), then go to Sketch > Project/Include > Include 3D geometry, and start clicking the Tspline faces where the cut will be made.  Then you can create a 3D spline curve, snapping its points onto the now purple Tspline geometries, which serves as a kind of "scaffolding." 

Finally you can do a sweep along that curve.  I did it in the Model environment, and first created a Construction Plane Along Path, placing at the end of the 3D spline curve.  Then I made a sketch on that construction plane, projecting/intersecting the 3d curve, and making a tiny circle centered on that, which served as the profile for the sweep. 

Then you can use that as the cutting tool for Split Body operation of the surface. 

Hope that helps!

Jesse