Noob Question: How to make a negative fillet

[scottdmills71]

freecad ver0.16
Linux Xubuntu 18.0471

I am trying to make a negative fillet between a cone and a flat plane. If you look at the included pic or file, I am trying to approximate the front of an SR71 spyplane, and I haven't quite figured out what to do at the weld point. If I were modeling it in reality I can do it, however I am not sure which tool/process to use within freecad.

[chrisb]

I am trying to make a negative fillet between a cone and a flat plane.

I am not really sure from your description where you want to have a fillet, but normally - and images found at the web support this - you have to make a union, select the intersection line and create a fillet.

Furthermore I would recommend to upgrade to FreeCAD 0.17.

[meme2704]

Furthermore I would recommend to upgrade to FreeCAD 0.17.

Do not listen, V0.16 is very good to start, unless you want to know the pangs of Partdesign
I'm not sure I understand the notion of negative net
but by doing the fusion cone + plan, it's very good

[TheMarkster]

With part design features mixed in with part operations maybe upgrading is not a good idea for this model? It contains with a part design pad. If you decide to upgrade be sure to save a backup copy of your file before trying to open in 0.17 or later just in case it causes problems.

Edit: Then again I opened it in 0.18, so...

[chrisb]

Furthermore I would recommend to upgrade to FreeCAD 0.17.

Do not listen, V0.16 is very good to start, unless you want to know the pangs of Partdesign

Due to Abdullah's phantastic improvements of Sketcher I tend to recommend the current 0.18 version: Best solver messages ever. Best help on finding degrees of freedom ever. And it seems to be as stable as 0.17! Objections?

[bejant]

freecad ver0.16
Linux Xubuntu 18.0471
I am trying to make a negative fillet between a cone and a flat plane.

To me that's a positive fillet because it adds material to an inside edge (and to me a negative fillet would remove material from an outside edge).

I am not sure which tool/process to use within freecad.

To add to the previous replies, in FreeCAD we don't Fillet separate objects to fuse them together as though we are laying down a weld bead to join them. Instead the separate objects must be combined into one thing before a Fillet can be applied to where they met. To join separate objects use the Boolean Union tool:

after you create a Fusion of them, then you can apply the Fillets to the Fusion.

Furthermore I would recommend to upgrade to FreeCAD 0.17.

Do not listen, V0.16 is very good to start, unless you want to know the pangs of Partdesign

I disagree with the suggestion not to upgrade your FreeCAD version, especially because you can have FreeCAD 0.16, 0.17, and 0.18 all installed together on your computer. Version 0.17 brought big changes to the work flow in the Part Design WB, which you might as well learn if you intend to stick with FreeCAD.

With part design features mixed in with part operations maybe upgrading is not a good idea for this model? It contains with a part design pad.

My suggestion is that usually if you start in Part Design, stay in Part Design. But in this model a lot has been done after the Pads were made, so I'll suggest that you stay out of Part Design.

If you decide to upgrade be sure to save a backup copy of your file before trying to open in 0.17 or later just in case it causes problems.

Edit: Then again I opened it in 0.18, so...

And now there is a backup copy on the forum, and I have one too (although I may not keep it for very long).

Due to Abdullah's phantastic improvements of Sketcher I tend to recommend the current 0.18 version: Best solver messages ever. Best help on finding degrees of freedom ever. And it seems to be as stable as 0.17! Objections?

No objection from me because I have 0.16, 0.17, and 0.18 all installed.

[scottdmills71]

This is approximately the joint i would like to produce at the union point.

[chrisb]

This is approximately the joint i would like to produce at the union point.

Did you follow bejant's advice? That's exactly what he described.

[TheMarkster]

OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.14061 (Git)
Build type: Release
Branch: master
Hash: c4fc02cbcfff975712e977dc08f859fba71ba0ad
Python version: 2.7.14
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.2.0
Locale: English/UnitedStates (en_US)

I'm getting a crash (FreeCAD closes with no message) when I try to fuse these objects. Checking the ellipsoid shows some errors in check geometry test. Seems odd a geometric primitive would have issues. (Even a newly created one with default settings shows errors.) Maybe it's my config files? If the ellipsoid primitive is problematic, then another option to consider would be to create it by revolving a sketch.

[chrisb]

Seems odd a geometric primitive would have issues.

That is a known bug of the CheckGeometry tool. FreeCAD can't do anything about it, because the geometry check comes from the OCC kernel.