Loft between 3 faces / Smooth out model

[ruben_van_lerberghe]

Hi everyone,

This is my first project on Fusion although I have gone through tutorials and think I have a good understanding of the basics by now. It would be great if the following could be cleared up:

For the joint between the armrest, the back leg and the connection between the two armrests, I used loft. This however does not give me a smooth transition. I used Loft in other areas as well so I wonder if for this problem, I better use an other command? 

And if i want to smooth out other areas of the model, is it best to convert to T-Splines ? ( modifying the same joinery after converting it does not go well) 

Another issue is that when i want to shorten the back leg, the armrest goes down as well. I've tried removing constraints but this remains a problem where i can only redo the spline that makes the armrest. 

A more general question, and hopefully also appropriate to ask here: Looking at the design history, did I make mistakes/create potential issues in the future. Parts of this chair need to be CNC'd so I need to get this model ready for that process as well. 

Thanks in advance,

Ruben

[TrippyLighting]

 That is a nice demonstration of techniques I use often and it demonstrates well what makes it enjoyable to develop surface models in Fusion 360!

However, in the video Class A surfacing was mentioned a number of times and in past years there was an Autodesk University class named "Complex Topology and Class-A Surface Modeling with Fusion 360". 

Let's clarify that Fusion 360 cannot be used for Class A surfacing/modeling for a number of reasons.

The default stitch tolerance in Autodesk Alias, one of only a hand full of real Class A modeling software is 0.001 mm.

The tripod model I cannot even stitch at 0.01mm.  I have to increase the stitch tolerance to about 0.04mm before it stitches. 

 

The reason for that becomes pretty obvious when the model is examined with the curvature map analysis tool:

 

The curvature comb on the edge, which  was initially a perfectly smooth spline  after stitching decays into this horribly wobbly mess:

 

The reason for all this is that a 5 sided boundary patch in many instances creates anything but a very smooth transition as mentioned several times in the video. The right technique for really smooth curvature would be to dissect that 5-sided patch into three 4-side patches.

 

Alas, Fusion 360 does not really have any tools to do so.

I am not saying that it needs those, but I am saying that is one of the reasons it cannot really be used to Class A modeling because it lacks tools for certain things.

The 1st model shown in that video also exhibits some problems. As we basically skin across three profiles we don't have any control over the degree of the surface and as such the curvature of the surface. The surface is a 3-degree surface and requires too many control points to do that in one span. In this case the surface loses curvature continuity in the place where we introduce the intermediate profile and this can be seen very often in Fusion 360 models.

 

Neither of those is a problem for the model in this thread or for Fusion 360 as a whole, but it definitely isn't Class A modeling. It does however, sometimes very clearly show up in renders which is somewhat limiting. I personalty would call neither of these models smooth 😉

[laughingcreek]

@ruben_van_lerberghe -you can move the spline for the back rest off the plane if you want.

here's a screen cast-

https://knowledge.autodesk.com/community/screencast/8371a56d-f0b5-44bc-be87-c442a80d6f4d

not sure what you  mean with the stretchers.  can you sketch on a screen shot what you envision the joint to look like?

[ruben_van_lerberghe]

Thanks for the screencast, makes it perfectly clear.

I attached a sketch. So the purpose is that the stretcher wraps around the leg. ( That's why i thought of extruding the stretchers into the leg and then deleting the overlapping part) But I don't see how to do it.

[laughingcreek · Accepted solution]

it looks like you already did the back stretchers?

machining the stretcher  like this may be problematic.  I imagine you'll end up having the ends of the stretchers squared off, and insert them into sockets milled into the legs instead.

I noticed the stretchers are lofted, but you flat extruded the stringers between the stretchers.  that would have probably been a better approach for the stretchers as well (rule of thumb, if it's flat, you usually don't loft).

[ruben_van_lerberghe]

Yes I extruded them into the legs, i thought that was not the best way to do it.

Thank you for the tip on when to loft and when not. 

When you say machining will be problematic like that, do you mean getting that wrap-around shape at the ends with a CNC ? Because for the assembly I would probably look at using dominoes/metal rods between the 2 shapes. 

[ruben_van_lerberghe]

Thank you all for the help

[financeiroB8G9L]

Como  faço  para  conseguir esse arquivo? Obrigado

Translated

How do I get this file? Thank you

[CGBenner]

@financeiroB8G9L 

Hello, what file are you referring to?