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Need help with loft/some way to continue a sketch face
jaqbow
Member Posts: 4 ✭
Hey there! I need some help creating a very specific shape using functions. The shape is defined by the function y=2sinx and the intersection in the y direction being that of a semicircle with the radius of sinx, as you can see in the screenshot i provided.
So far I've tried watching a few videos on the loft feature (with the center semicircle and a very small one at the corner), however i cant get it to keep all of the semicircles parallel, nor have them keep the specific radius. I really just want to know if this is even possible in onshape or not. You can see te loft doesnt even go straight it gets larger and then smaller
Here is a link to a 3d desmos graph with he shape since i don't think I am good at explaining it: https://www.desmos.com/3d/zf7myjfcdu
Comments
You're not going to easily (if at all) be able to make a surface which is mathematically exact with NURBS, especially with the standard Onshape surfacing tools. You can definitely get a close approximation. What kind of error band are you ok with? How will this be manufactured?
If each cross section parallel to the right plane is a semi-circle, I might try adding a few more cross sections to your loft. That may help convince the loft tool to parameterize the surface a little closer to what you want.
I would also try boundary instead of loft (however that will not allow internal guides), or fill instead of loft.
Depending on what condition you want the shape to be at the right plane, you may want to model the full shape, not 1/2 and mirror it.
If you really need this to be "perfect" you might be able to write some FeatureScript to create a surface from raw control points that you define using your function. With the correct weights, a degree-3 NURBS curve can be an exact semi-circle, and then you would just need to pick a degree which is good enough to approximate the sin function for the other axis.
There's also this custom feature which might work, but it will approximate the math with a lot of points which may or may not be accurate enough for your needs:
https://cad.onshape.com/documents/57a62df8e4b03de4c9fcf154/w/f6d71f3d862b522902efcd68/e/ece65382fcd820281a9ee704