Fillets on sharp edges

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mcstinger
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Joined: Fri Jun 04, 2021 11:18 am

Fillets on sharp edges

Post by mcstinger »

Dear members,

I would appreciate help with solving my "problem". I have created a guitar body, where I would like to create fillets on the upper and lower body edges (partially marked by yellow line). I am not able to create a fillet bigger than about 1 mm. I would like to go to 5 mm. I understand, this is probably due to those quite small diameters used in sharp body corners.

I have tried to do this through sweeping a sketch along body edges. I was successful on straight lines and body fillets between those straight lines. But it fails on sharp outer corners. Otherwise, the body is almost completely finished already, I have simplified the project just to basics.

I believe, it somehow can be solved. If I imagine real milling tool, there is no problem. But I am not able to achieve the result in Freecad. Still quite newbie, maybe I made some basic mistake in my approach to the first sketch, I don't know.

Thanks in advance for any hints. Freecad is 0.19, 24291, project file is attached.
Screenshot 2021-10-20 20.41.39.png
Screenshot 2021-10-20 20.41.39.png (97.65 KiB) Viewed 1528 times
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KG_f_01.FCStd
(29.99 KiB) Downloaded 31 times
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papyblaise
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Re: Fillets on sharp edges

Post by papyblaise »

it is the R = 1.7mm which block it is necessary that you resoude to make them at 5mm too
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Shalmeneser
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Re: Fillets on sharp edges

Post by Shalmeneser »

Fillet < 3.8 works.
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Shalmeneser
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Re: Fillets on sharp edges

Post by Shalmeneser »

With a substractive pipe, there are problems in some corners (see picture).
Attachments
Capture du 2021-10-20 21-26-49.png
Capture du 2021-10-20 21-26-49.png (70.37 KiB) Viewed 1480 times
KG_f_01_SHALM.FCStd
(124.79 KiB) Downloaded 19 times
mcstinger
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Re: Fillets on sharp edges

Post by mcstinger »

Shalmeneser wrote: Wed Oct 20, 2021 7:21 pm Fillet < 3.8 works.
I would like to go to 5 mm... And yes, subtractive pipe has a problem in corners. Probably for the same reason as a fillet.
freedman
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Re: Fillets on sharp edges

Post by freedman »

I'm thinking take the radius out of the sketch and apply fillets to get what you want. I applied to the top edge first. Pic, I did three edges.

I think someone will need to do this in Part.
Attachments
fill1.png
fill1.png (195.45 KiB) Viewed 1351 times
freedman
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Re: Fillets on sharp edges

Post by freedman »

Here is a design letting FreeCAD do those sharp radius. I'm trying to think about what mixing radius looks like, I think there are limits to that...
Good luck
I just noticed I used a radius of 8mm. I had no problem changing to 5mm.
Attachments
fill2.png
fill2.png (165.66 KiB) Viewed 1318 times
KG_feedman.FCStd
(310.14 KiB) Downloaded 28 times
domad
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Re: Fillets on sharp edges

Post by domad »

mcstinger wrote: Wed Oct 20, 2021 7:01 pm .....
Hi mcstinger, greetings to the Community!

The 5mm top fillet can be easily achieved as demonstrated by @freedman by changing the base fillets from 1.7mm to 8mm.
The problem is described very fully in the replies by @papyblaise and @Shalmeneser.
This does not mean that FC is not able to do it, on the contrary these problems enhance the power and versatility of FreeCad.
Therefore, to obtain the 5 mm upper edges, while maintaining the 1.7 mm (or even smaller) base ones, it is necessary to proceed in several phases with the "Subtractive pipe" function using and positioning profiles that show the 5 mm connection. and using suitable sweep paths placed on the edges of the shape.
Undoubtedly it is a fairly complicated modeling due to the alignments of the profiles to be positioned orthogonally to the paths, and to be carried out with a lot of patience.
The attached images show an acceptable result (8.5 Mb file) also in function of an export for 3D printing.
Attachments
Body KG.png
Body KG.png (238 KiB) Viewed 1231 times
Body KG-2.png
Body KG-2.png (193.76 KiB) Viewed 1231 times
Body KG-3.png
Body KG-3.png (195.75 KiB) Viewed 1231 times
Body KG.gif
Body KG.gif (410.88 KiB) Viewed 1231 times
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Shalmeneser
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Re: Fillets on sharp edges

Post by Shalmeneser »

domad wrote: Thu Oct 21, 2021 2:45 pm Undoubtedly it is a fairly complicated modeling due to the alignments of the profiles to be positioned orthogonally to the paths, and to be carried out with a lot of patience.
* Create the sketch (upon any plane)
* Leave the sketch
* Modify its Map Mode :
** Clear Plane
** Select Normal to Edge
** Select line (Reference : line from the base sketch)

(* Modify Map Path Parameter : 0=here, 1=other vertex, 0,5=middle, ...)

See my file.
freedman
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Re: Fillets on sharp edges

Post by freedman »

Nice post domad. I was planning on reposting today to express that it is possible but it will take alot more work.
Thanks
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