Yet another exhaust manifold

[Olav]

Dear FreeCAD gurus,

Please consider my model, which most of you will recognise as yet another attempt to model an exhaust manifold:

Schermafdruk_2020-12-28_00-32-42.png (251.95 KiB) Viewed 1252 times

I thought I had a great plan: create some 3D paths in the Part workbench, use Part Design to sweep some circles of the right diameter along those paths (using shapebinders), fuse (boolean union) the resulting bodies into one, then apply inward thickness to hollow out the entire thing.

Unfortunately though, FreeCAD refuses to either a. fuse my "pipe" sub bodies and b. apply thickness to them, even individually.

Here is the result of a fuse operation on those first two (still solid) pipes:

Schermafdruk_2020-12-28_00-36-38.png (236.53 KiB) Viewed 1252 times

There are no errors in the Report view so it appears that as far as FreeCAD is concerned the operation was successful. Of course I beg to differ.

As a test I tried to use the thickness tool to create a pipe from just one of those solid bodies from the first picture above. This results in the cryptic error message "BRep_API: command not done":

Schermafdruk_2020-12-28_00-44-41.png (8.27 KiB) Viewed 1252 times

Which gives me exactly no useful information for solving the problem.

I'm beginning to think I must have done something stupid or naive (wouldn't be the first time) in setting up this model. Should I have created my sweep "paths" differently? Or am I really asking too much of FreeCAD to do? I mean if it can create the sweep successfully it should be able to perform other operations on it too, n'est-ce pas?

Any pointers for finding a solution would be very welcome.

I cannot attach the file because it's 2.6 MB for some reason, and the forum doesn't accept it.

I uploaded the file here: https://we.tl/t-27Hc1BrXYw, I hope that's acceptable.

FreeCAD info:

Code: Select all

OS: Ubuntu 18.04.5 LTS (XFCE/xubuntu)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.
Build type: Release
Branch: unknown
Hash: 72ec38be5dbb4370965fc35f9b5bce2bef38fb39
Python version: 3.6.9
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: Dutch/Netherlands (nl_NL)

[chrisb]

Forget about Thickness in such cases. It often fails as soon as non-circular curves are involved. And the sharp corner where the tubes meet is not at all thickness-friendly either.

I would recommend to model the innards with two additional sweeps based on the same paths and subtract these innards from the whole tube.

[Olav]

Thank you for your reply!

Forget about Thickness in such cases. It often fails as soon as non-circular curves are involved.

Just for my understanding, what do you mean with non-circular curves?

And the sharp corner where the tubes meet is not at all thickness-friendly either.

I would recommend to model the innards with two additional sweeps based on the same paths and subtract these innards from the whole tube.

That seems like a good approach, I will try it.

Meanwhile do you have any idea why I can't fuse those two bodies? Are they not allowed to overlap/intersect or something?

[chrisb]

Just for my understanding, what do you mean with non-circular curves?

I meant curves that cannot be described directly by straight lines or circular arcs. E.g. a cube or a cylinder or a combination of those would be ok, while your sections create curves which can be described by B-splines.

[papyblaise]

After 3 hours of severe headache, I got there
first I noticed that it was symmetrical, so I made half of it and Miror
I used your elements, but after some attempt it was a failure to finish with PartDesign, so I used Part to do the merges and the connection with pipes so that the whole is connected as it should
In PartDesign, I made the 2 pipes by directly drawing the material thickness, then, by copying them into a Part file, I merged, then I made 2 Sweep from the hole that I subtracted
unfortunely , the file is to large (10.5Mo) and I don't know any cloud

[Olav]

After 3 hours of severe headache, I got there

I'm sorry for your headache. Your picture looks good though! Would you be willing to upload the FCStd file to https://wetransfer.com? I'm not sure that's the best but it works.

[Olav]

@papyblaise you can also think about having a github account where you can easily share large models from. If you need help with this, let me know. I can help you set one up.

Github is cool. Off topic, but just searching for "free upload" turns up a lot of useful sites. Perhaps we could have a poll to determine which is the best for use on this forum.

[Kunda1]

Github is cool. Off topic, but just searching for "free upload" turns up a lot of useful sites. Perhaps we could have a poll to determine which is the best for use on this forum.

Off-topic, but we hope to increase the upload limit at some point. We do need some phpbb help if anyone is interested?

[Olav]

Off-topic, but we hope to increase the upload limit at some point.

That would be lovely.

We do need some phpbb help if anyone is interested?

Exactly what kind of help do you need?

[chrisb]

I'm not sure that it is a good idea to increase the limit. Especially for error finding it is quite helpful to have reduced models. Increasing the limit may just increase the noise. Among all these models uploaded, how many are too big and have to be outsourced?