Shelling part of a solid body and leaving another part solid

[mflail86]

Hi all,

I am fairly new to fusion 360 and cannot figure out how to make a part of my model solid and the handle of the body shelled.  If anybody knows how to accomplish this or if it is even possible please let me know.  The part is split where the highlighted plane is and right now is completely shelled. Ideally I want the front to be solid and the back 3/4 to be shelled to hold liquid.

Thanks,

Matthew

[Oceanconcepts]

Well, one approach to try would be to utilize Fusion's amazing Boolean tools. Split the body before shelling, shell the end you want to, then Combine them back together. I've done similar things and had it work well. Another path might be to split the shell and fill the lower part to solid using a sliced off copy of that part of the pre-shelled body. At least in direct modeling, I've learned not to be afraid to split and rejoin elements if I need to treat them differently. The result is nearly always seamless.

[mflail86]

Great, thanks Ron. Splitting the body prior to shelling worked but only when I shelled both ways so I now have a disjointed body.  Is there a way to combine and make the bodies equally proportionate to one another? Or blend the two bodies to make a smoother transition? I tried using the thicken tool to no avail and offset the smaller body but it still gives a disjointed appearance in certain places.

-Matt

[Oceanconcepts]

So you're seeing outside surface discontinuity after shelling one half?  I've had really good luck with splitting and recombining parts perfectly. 

Actually, I think I was making this harder than it needs to be. If you just make two copies of the body, split one where you want and discard the part you don't want to be solid, shell the other body, then Combine the two, that should give what you want- if I'm understanding correctly.

[jakefowler]

Hi Matt,

Sorry we hadn't followed up on this sooner - but was the shell not working if you selected 'Inside' or 'Outside'? If so, this is definitely something we'd like to take a look at: we would expect this to work regardless of the direction selected. If you are able to send us the file (you can save the Fusion 360 design locally using 'Export Archive' from the application (3-bar) menu), we will look into this.

Many thanks!

Jake

[mflail86]

Hi Jake,

Sorry it took so long for me to get back to you.  To answer your question, yes, it would not allow me to shell inside and was very confused when i tried to shell outside as well. It only worked when I shelled both ways at .04in and higher.  What I would like is a continuous body from end to end without the step in the front of the object but the object shelled in front where i have the plane set now.   I attached the file so if you could take a look, that would be great.

Thanks guys,

Matt 

[mflail86]

Sorry, i want the larger section shelled and the front to be solid from that plane forward.

[jakefowler]

Hi Matt,

Thanks for getting back! Just to confirm, what was the thickness you wanted to shell inwards by?

I was able to get the model to shell inwards at up to 0.06", although I encountered a few unexpected issues along the way, which I will follow up with the development team. I got the inward shell using the following steps:

1. Edit Split4 in the timeline (split operation just before the shell), then OK (if I didn't do this, the shell body disappeared when editing the Shell - this is one of the issues I'm following up on)

2. Edit Shell4, change the direction to Inside

The thread at the end of the workflow also encountered an issue after doing this (it partially disappeared) - I was able to work around this issue by offsetting the original thread feature (basically moving it out of the way) and applying a new thread feature on the same face. But this shouldn't be necessary, and this is also something I'll also follow up on.

I've attached the file I was working on. If you need to shell to a larger thickness, let me know, and I'll see if we're able to achieve that thickness.

Thanks!

Jake

[mflail86]

Hi Jake,

Thats awesome. Thank you again!

I was originally trying to get the shell to .08in inside so if there is a workaround to do that please let me know. 

The rest of the model looks great.

-Matt

[jakefowler]

Hi Matt,

I’ve attached the model shelled to 0.08in – I achieved this by switching some T-Points to Star Points on the original T-Splines model, which slightly improved the surface flow. Note that this has changed the shape a bit (comparison below), so best to check that these changes are acceptable:

I’ve written up a detailed analysis below, in case this is useful for future reference 🙂

Hope this helps!

Jake

===============

The shell issues appear to be emanating from this region of the model:

A trick I often use to analyse this kind of thing: create a Base Feature, and in the Patch workspace, use the Offset tool to ‘simulate’ the shelled result by creating surface offsets of your model faces. If any faces fail to offset or give strange looking results, this might be a cause for concern. In this case, one of the faces 'scrunched' together in this region when offset inwards by 0.08mm:

For shell failures on models originally created with T-Splines, there’s often some tweaks you can make to the T-Splines model to help. For this T-Splines body, I first checked the control polygon of the model. You can see this by editing the Form in the timeline, selecting the T-Splines body, and toggling its Display Mode (Alt-1/2/3 on Windows, or Control-1/2/3 on Mac). 

The above image shows that the control polygon is a bit ‘stretched’ in places, and not all control points are neatly aligned: generally it’s best to check the control polygon during/after the T-Splines modelling process to look out for these issues, as these can cause unwanted ‘bumps’ in the resultant T-­Splines surface, and in turn may affect things like downstream shelling.

I also tried using the Repair Body tool to analyse the geometry. This showed that the model has a few 3-sided faces. Again, this can be a warning sign – in general T-Splines shapes are smoothest when all (or nearly all) faces are 4-sided. 

The Repair Body allows you to toggle T-Points for Star Points (the video here explains what these points are). By toggling the T-Point next to the 3-sided face for a Star Point, the 3-sided face (and its symmetric equivalent on the other side) becomes 4-sided, changing the shape of the model slightly. In this case, this made enough of a difference to resolve the shelling problem.

As for resolving the stretched control points & alignment... this one is a bit harder to fix without needing to reshape your model again. This situation often arises by trying to do ‘too much work’ with a small number of control points. So perhaps it’s best to start this model with a larger number of control points. Here’s a video showing how I might create a similar shape, starting with a 4 x 2 x 2 faces T-Splines Box. Note that I’m mainly moving entities in groups, and only making small ‘tweaks’ when moving individual points:

http://screencast.com/t/U9KRwSjoVPFi

By moving groups of faces/edges together, and not pulling any individual points too far, the control polygon keeps fairly even proportions, and the curvature of the resultant shape flows smoothly:

===============

[mflail86]

Jake,

Thanks again for the help and detailed rundown of this issue. The model looks great and I really appreciate you taking the time to look at it. 

The only thing I'm wondering about at this point is how I might be able to scale the model up or down. From what I've heard from fellow classmates, there should be a scale option in the modify section but I don't see it. Am I missing something?

-Matt