Chamfer problem (driving me nuts)

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dgvirtual
Posts: 11
Joined: Sun Sep 22, 2019 9:08 am

Chamfer problem (driving me nuts)

Postby dgvirtual » Sun Sep 22, 2019 9:45 am

Hello everyone,

I am constantly hitting my head against chamfer problems (or fillet - if chamfer does not work in a certain case, neither does the fillet).

If I apply chamfer to a more complex object, sometimes it disappears completely, and sometimes I get artefacts, like the object looses some of it's faces.

I am attaching a part that I have applied chamfer on:
chamfer.FCStd
(58.44 KiB) Downloaded 10 times
And I also attach an image displaying the view before chamfer and after chamfer:
chamfer.png
chamfer.png (8.08 KiB) Viewed 421 times
Any advice on how to work around such problems? it is driving me nuts!

Useful info about the system [manually added things in such brackets]:

OS: Linux [Ubuntu 18.04 LTS]
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.16093 (Git)
Build type: Unknown [snap package]
Branch: master
Hash: 690774c0effe4fd7b8d2b5e2fb2b8c8d145e21ce
Python version: 2.7.12
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.0.0
Locale: English/UnitedStates (en_US)
Last edited by dgvirtual on Sun Sep 22, 2019 12:16 pm, edited 2 times in total.
openBrain
Posts: 3402
Joined: Fri Nov 09, 2018 5:38 pm

Re: Chamfer problem (driving me nuts)

Postby openBrain » Sun Sep 22, 2019 1:18 pm

Refining "Pivot-modulis" fixes the problem by removing unneeded edges. ;)
Attachments
chamfer_OB.FCStd
(67.87 KiB) Downloaded 8 times
dgvirtual
Posts: 11
Joined: Sun Sep 22, 2019 9:08 am

Re: Chamfer problem (driving me nuts)

Postby dgvirtual » Sun Sep 22, 2019 3:31 pm

OMG, it was so easy... Could you tell me what exactly did go wrong with applying chamfer before refinement?

Donatas
openBrain
Posts: 3402
Joined: Fri Nov 09, 2018 5:38 pm

Re: Chamfer problem (driving me nuts)

Postby openBrain » Sun Sep 22, 2019 3:37 pm

I can't say exactly but I guess OCC is disturbed by aligned edges where ones are "true" edges and others are "seam-like" ones. ;)
kisolre
Posts: 1637
Joined: Wed Nov 21, 2018 1:13 pm

Re: Chamfer problem (driving me nuts)

Postby kisolre » Sun Sep 22, 2019 4:31 pm

OCC (or FreeCAD chamfer/fillet feature?) tries to continue chamfer/fillet along tangential edges. And here tangential is the extra edge - the two faces on sides of this edge are at the same plane - no angle between them - it fails to calculate offset of the cutting plane to make the chamfer. Something like probably.
dgvirtual
Posts: 11
Joined: Sun Sep 22, 2019 9:08 am

Re: Chamfer problem (driving me nuts)

Postby dgvirtual » Sun Sep 22, 2019 5:22 pm

OK, what about this part: it is produced from a sketch that has been padded 10mm. Chamfer on a refined shape Pad001, face13 or Face14 (the two big faces) fails (the shape disappears, and chamfer object is shown with an exclamation mark. I do not include the chamfer operation in the file I attach:
chamfer2.FCStd
(17.87 KiB) Downloaded 9 times
Is there a way out here? I know the contour is strange, perhaps I could make it smoother, but still...
chrisb
Posts: 22430
Joined: Tue Mar 17, 2015 9:14 am

Re: Chamfer problem (driving me nuts)

Postby chrisb » Sun Sep 22, 2019 5:30 pm

Now the true reason for your persisting troubles becomes clear: You have a poorly constrained sketch.
Snip macro screenshot-e03a86.png
Snip macro screenshot-e03a86.png (3.26 KiB) Viewed 366 times
You have only handmade, i.e. "almost"-tangencies and fillets and chamfers cannot handle these very tiny angular deflections. Rework your sketch to use geometric constraints first, and finally add the preferably minimal set of dimensions.
dgvirtual
Posts: 11
Joined: Sun Sep 22, 2019 9:08 am

Re: Chamfer problem (driving me nuts)

Postby dgvirtual » Sun Sep 22, 2019 7:01 pm

chrisb wrote:
Sun Sep 22, 2019 5:30 pm
Now the true reason for your persisting troubles becomes clear: You have a poorly constrained sketch.Snip macro screenshot-e03a86.png
You have only handmade, i.e. "almost"-tangencies and follets and chamfers cannot handle these very tiny angular deflections. Rework your sketch to use geometric constraints first, and finally the preferably minimal set of dimensions.
OK, thanks. I tried using less dimensions on this part and chamfer did work. The problem was I was trying to replicate a part that was less than perfect in it's dimensions, but instead of improving on it I made it even worse.

Good to know it is mostly my fault – my lack of experience is easier to fix than fixing bugs in Freecad. Thank you all!
dgvirtual
Posts: 11
Joined: Sun Sep 22, 2019 9:08 am

Re: Chamfer problem (driving me nuts)

Postby dgvirtual » Tue Oct 01, 2019 7:02 pm

Now I have a fully constrained sketches, geometrical shapes, I have remove unnecessary edges, and still fillet (an chamfer) fails. What could possibly be the problem here?
test.FCStd
(80.65 KiB) Downloaded 8 times
Attachments
test-fillett-fails.png
test-fillett-fails.png (24.71 KiB) Viewed 285 times
kisolre
Posts: 1637
Joined: Wed Nov 21, 2018 1:13 pm

Re: Chamfer problem (driving me nuts)

Postby kisolre » Tue Oct 01, 2019 8:36 pm

There are seams from second pocket circles. that small one in the middle creates problems with bigger chamfers. .
.
chamfer_seam.JPG
chamfer_seam.JPG (60.13 KiB) Viewed 272 times
.
Weird thing is that even after refining the pocket those seams still manifest
.
chamfer_seam_refined.JPG
chamfer_seam_refined.JPG (66.71 KiB) Viewed 272 times
.
In such cases you can use arcs instead if circles to have clear devined start/end of ark and seam position outside the cut.