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Creating Smooth Lofts
zach_morris
Member Posts: 25 ✭✭
I was having issues creating smooth lofts on this helmet. https://cad.onshape.com/documents/b2f8fe08679dabeeac1950da/w/17ab1e761096c9e8b822b024/e/0182e42400e098613859acbe After 3dprinting it I determined I need to resize the helmet a bit so I decided to redo the base sketches use Bézier curves instead of splines. Which you can see in this newer version. https://cad.onshape.com/documents/c8d4ffa4f0b6e177f63ac6bd/w/73d5a87a693f9ba067fc2449/e/48df10242fc14a58513304f5
However, the issue I had was that you cannot split the Bézier curves which I needed to do in order to create the proper lofts for the helmet. My solution was to create guidelines in a new sketch and match them up as close as possible to the original Bézier curves to guide the lofts, but I'm still getting creases where the two lofts meet at the crown of the head.
Right now I'm putting a constraint between the separate spline control handles to make the parallel with the thought that the parallel constraint would make the transition between the splines smoother, but when I use curve analysis the curves still aren't perfectly smooth between the two.
Best Answers
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GregBrown
Member, Onshape Employees, csevp, pcbaevp Posts: 253 
Replace Loft 2 with a Fill and make sure to select Tangent continuity for the edges of Loft 1 that you use…
(The way you have created it, Loft 2 is degenerate at both ends with means it will be problematic to make any smooth connection…)0 -
MDesign
Member Posts: 471 ✭✭✭
did you see this post?
You had 2 things that were not going to allow a tangent surface. one you had sketch curves selected to create an edge for your surface Loft 2 instead of the edges of Loft1. and Portrait Guidelines sketch curve was not set to perpendicular or normal to the right plane.
0
Answers
When two curves meet at a point, they have G0 continuity. When they are tangent, they have G1 continuity. Zebra stripes will be smooth with G2 continuity, which means that the curves are not only tangent, but they match curvature.
https://cad.onshape.com/help/Content/surfacing.htm
@zach_morris are you able to turn copy permission on for others to inspect closer?
Replace Loft 2 with a Fill and make sure to select Tangent continuity for the edges of Loft 1 that you use…
(The way you have created it, Loft 2 is degenerate at both ends with means it will be problematic to make any smooth connection…)
Wouldn't this make the inside of the helmet solid and unwearable though? The ultimate goal of this project is to 3dp the helmet and wear it.
This resource is very thorough thank you. Looks like it's time to hit the books!
Changing the cap loft2 to be tangent to the surface it mates too should help you.
It says that all Onshape users can copy. I can only give general people using the link export permissions if I have their email, I tried adding your username, but it didn't find you.
I'm not sure what was going on. when I first tried it it was view only. I made a copy and posted above what I saw.
Also anywhere you have a guide/sketch going into the "right" plane you need to constrain it to be normal to the right plane or set the curve control line perpendicular to the right plane.
One thing I like to do when I'm working toward smooth surfaces is also turn on phantom tangency lines. Makes it easy to see if things are tangent as you move forward.
Not if you choose these edges:
I did this, and it looked a lot better in the colormap, but ultimately there's still a seam. I'm going to print it and see if it even shows up.
I learned a lot from the link you posted. I normally use the iPad version, and Bézier curves are not even an option on there.
So I redid the sketch and the guidelines with beziers instead of splines. Was able to get the curvature analysis much better, but with how some of the curves are I had some of the bezier control arms crossing center. It looked a lot better on the curvature analysis, but when I made the lofts and fills still ended up with the same seam, but slightly less pronounced. I'm going to print it and see it's even noticeable. Any more efforts will have diminishing returns, and if you can't see it in a 3dp not worth going in and cleaning up.
I was able to clean it up no issues. One of the things that tripped me up early learning stage was was for the tangency selection to work on profiles and guides you had to select the edges of the surface and not the underlying curves and sketches. Even if you directly select the tangent face it won't work
Not sure I'm following on this one. When I'm editing the fill on the linked model the original loft surface is not visible, so I only have the guidelines and other sketches to work off of. Could you send a link to your version so I could take a look and see what you did?
did you see this post?
You had 2 things that were not going to allow a tangent surface. one you had sketch curves selected to create an edge for your surface Loft 2 instead of the edges of Loft1. and Portrait Guidelines sketch curve was not set to perpendicular or normal to the right plane.
Before The Fix
After The Fix
Edited my last post to add links and before/after zebra image
I missed that one. But I realized I marked the surface as hidden in the surface tab so I couldn't see the surface to select it to make loft 2. This is making a lot more sense now though. I gave it a test run and that solved my problem! You wouldn't think intuitively that the edge of the guideline and the edge of the loft itself would make any difference.
When you think about how a computer program does what it does it does make sense…. at least to me it does. Can it be programmed not to matter? maybe, but that's above my pay grade.