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Help with loft errors?
jim_zamecnik
Member Posts: 5 ✭
Hi - Brand new Onshape user…3 days in. Fairly experienced with 2D (LibreCAD) but this has been a challenge. I've been through some of the intro tutorials and a ton of videos and googling for clues. My interest is modeling rc glider fuselages, potentially for making 3D printed molds.
https://cad.onshape.com/documents/e8ab9d2dda466efe61e6b654/w/06537b56c3e593568ddc42ee/e/dde4361032512bd6dd957a7f?renderMode=0&uiState=697ea8cf9c605a148af80a5b
So this is where I am….a fuselage half I'm attempting to loft. I cannot get it to follow the splines defining the edges of the "Fuse side" sketch. I'm actually happy with it behind former 4, the way the top line ended up being curved. A happy coincidence. The issues are mainly ahead of former 3. The top surface between formers 3 and 4 will be removed when I cut the wing saddle, so even though it looks a bit odd it's probably fine.
Any pointers are appreciated.
Also, if anyone can tell me why the "former 4" sketch is undefined when the nearly identical formers 1, 2 3, 5 & 6 are all fine, it will save me pulling the last of my hair out. Constraints and getting sketches defined has been a major roadblock for me. I understand the principal but end up with blue or red lines anyway. I end up throwing random constraints at it or selecting the whole sketch and applying the "fix" constraint. Sometimes that works!
Thank you.
-Jim
Comments
@jim_zamecnik
Former 3 and 4: End point is not constrained to the origin, even it is positioned very very close to it.
Close-up:
Using the "Fix" does lock them in place, though not necessarily to THE place. ;0)
Try not to use the "Fix". Else, the loft may find the curves you use do not actually meet, so it can't ctreate closed surface:
After fixing that, the loft works:
This model can be made to work, but I suggest you go through the surface modeling excercises in the learning section. You did not pick the best approach from the start, so you end up having avoidable troubles.
Try to start with the larger image. Visualize the general shape (E.G. by 3D curves as seen above) before attempting to create formers. Make the shape first, add details like elevator mountig surface (much) later, and so on.
https://cad.onshape.com/documents/62cc9f1146682aec3efd07d8/w/9c9fba56d365aecbda696ec8/e/4229468f0fb0d5ee102c5ad6?renderMode=0&rightPanel=appearancePanel&uiState=697f85e02dd498a7d3f15908
Wow Martin, thanks so much for the help. That looks exactly how it looked in my brain! :-)
I will compare your drawing to mine and see where I went wrong. I did zoom in and find some missed connections, but I guess not all. Still a lot to learn after 4 days of Onshape experience :-) I was planning on starting fresh to improve the workflow; now I have a few more things to be aware of.
I'll go through the Learning Center surface modeling exercises. I knew I probably wasn't doing things in the best order. I started out following this YouTube tutorial but then I wandered off on my own when I "thought" I knew what I was doing.
Thanks again!
If anyone goes to my original document link posted above, I've gone back in and tried to see where my mistakes were. And made a giant mess in the process. I'm going to look over Martin's corrected version, then start from scratch.
I knew this 3D CAD thing was going to be an adventure when I started!
@jim_zamecnik
Haha, Yesss. Looks easy from the outside until you meet the crucial and unforgiving details within. I'm an aeromodeller myself, so I think I understand your situation.
With them points are all being on each other, there is one important thing: They do not acually sit on each other (or on a curve) until they are logically constrained to each other. Two fixed constraints on two independent points will not create any relationship between them. Once you get that, it becomes much more relable. taking care of tangency is another 'secret' trick: If neglected, missing tangency in the curves you start with, will lead to warped surfaces downstreams. That is also true for the guide curves.
One more hint: If you model half of the fuselage (which I recommend to save on work and reduce the error rate), create some helper geometry to help with tangency after mirroring the other half. Look at what I did with the nose: There is an extruded surface that is only used to make sure the two halves meet smooth and with no bump at the mirror plane. Good luck!