Another small loft problem

[dantahoua]

Hello!

One of my first post here. I always manage to find answer myself but this time I tried everything and cannot find a solution... I prefer not to use the form/mesh mode as I found it (with my experience) less precise...

So the problem I have is that the loft always make a small hollow on the center line. I kind of understand in a way why he is doing that and at the same time I'm like "why don't you follow my rail?"!!!

This hollow is really obvious when I manufacture the piece on my CNC...

You can see on the picture, I want the part highlighted in orange to be "flat on the center line" as my upper bout rail is.

I think Fusion struggle here as I go from one curve to a really different one with 2 rails constrain. It is less worst if I loft from the upper bout curve to the center point and use the center curve as rail.

I join also an export of my Fusion 360 file if someone want to look at it, All the strating sketch are there as also all my test (with mesh and other surface).

Do you have any idea? 

[TheCADWhisperer]

Why are you not capturing design history?

[TrippyLighting]

1. As a beginner you should not work without the timeline enabled.

2. Do not piece together the loft profiles, and rails from several segments. It can work but often results in problems.

3. If you to piece those together, at the very minimum they need to have tangent constraints between them, better G2 curvature continuity.

4. Only Sketch half of everything.

5. This should be one single loft for half of the instrument.

This is NOT a beginner project. We have a current thread going on where another user string something very similar with a Gambasso ( I guess Viola Da Gamba like size). 

What is good is that you are not trying to use too many rails or profiles.

This obviously is not your instrument (its from that other thread) , but this can be done:

[dantahoua]

Thanks!

1-I add to remove timeline to try Form and Mesh to see if I could do something better with it... I should have uploaded my first file, the one "before" the mesh... But you know when you start to try a lot of stuff...

2-Ok, will try but sometime I have at least 4 sides to take into account...

3-Not sure I understand this one, can you point me somewhere with a good explanation?

4-In fact I always start with the half sketch and more with guitar as my center line is often the core of the design. On this one I thought everything was good before I manufacture the part that's why there is everything, but I'll strat over from scratch with only the "half". Here you just confirm me it's a good practice! 🙂

5-But the loft could go from many curve? I would check the post you're referring to. I never said it's a beginner project, did I post it on the wrong place? I'll start it from scratch next week. If you have other suggestion, I'll take them into account.

I alway try to keep everything as simple as possible, so when you say to use just one loft for one half, I wish I really mange to do that. I try to use simple curve and basing sketch tools for my curve to be as much smooth as possible...

Thanks a lot. 🙂

[TrippyLighting]

Do you still have that initial design with the timeline and all or at least most of the sketches ?

[dantahoua]

This is the only one I have with less stuff in it. All the original Sketches are in there.

The guitar shape is imported from Illustrator.

Then I use the lower/middle/upper bout line to create plane and to create my spline for those curvature.

I have to go now, I'll be back tomorrow evening. I'll be able to try to make another from sratch if it could help you to help me! 🙂 Ah ah. Thanks a lot for your help. I think I'm not that far from understanding...

[TrippyLighting]

Building an instrument is precision work, you know that better than I do.

CAD work also requires deliberation and precision to achieve great results.

Thus use that imported garbage from illustrator for visual reference and NEVER build geometry from it!

[dantahoua]

Ah you're right! Now that I am more confident with sketch in Fusion I will
do it in Fusion with spline. Should take me 10min to do it tomorrow! 😊

[dantahoua]

Here is the new file. I made the guitar shape with spline. I tried to loft but seems still to have a odd shape at each extreme bout of the center line. Maybe you could explain me what would me the better way to loft here. 🙂

[dantahoua]

So I tried a lot of stuff with my new file (see previous post), still not be able to have the loft perfectly regular. There is probably something I don't see or do not understand...

[Johnc911]

can you elaborate on where the problem is with your latest file? maybe with a screenshot showing the area that you think is off.

[TrippyLighting]

Looking at your file I would concur that you are missing several important CAD concepts and lofting anything is really too advanced of a topic. For example your symmetry axis does not coincide with there sketch origin.

I'll create a screencast later of how I would do this. But for now I have to actually attend to my day job 😉

[dantahoua]

Just for information, here is some screenshot, looks like it's good but it is not...

[dantahoua]

No problem. Thanks for your time, I'll wait your screencast. Sure I miss some basic CAD concept. I'm a quick learner, just show me and I'll understand.

When you say my symmetry axis is not good, I thought making a construction plane following my center line before mirroring the half guitar would be enough... So if I understand well, my "center line" should be aligned with the origine X or Y for exemple?

Anyway, I have to work me too. 🙂 

[TrippyLighting]

You've not identified the real problem area. When you mirror the geometry you'll find that tangency is missing across the symmetry axis.

[TrippyLighting]

Again, screencast will follow later.

[dantahoua]

Oh waou!

I just tried to remove my "offset" curve I made as I saw that when you offset a curve seems it doesn't keep the curvature informations like tangent. I thought it would be simpler with this "offset" curve for the flat plane but in the end it adds more curve to the design...

So I went with a simpler one but I'm still ending with something odd!

Can't wait to see your screencast and understand what I miss !!! 🙂 Many thanks in advance.

Maybe would be great to have those kind of screencast as "reference" for people like me to avoid basic CAD errors... Just thinking out loud. 🙂

[Johnc911]

Also look at how @TrippyLighting 's Zebra analysis is higher fidelity than yours. Use the "high quality" option in Zebra analysis to get this.

[TrippyLighting]

Also, I've found that often, depending on the model it helps to set the display detail control from "adaptive" to "fixed/high".

[TrippyLighting · Accepted solution]

Here is a screencast I created late last night: