Solved - Best way to add boss up to a curved surface?

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tony902
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Joined: Sun Feb 05, 2023 9:21 pm

Solved - Best way to add boss up to a curved surface?

Post by tony902 »

Hi, newbie to FreeCAD (0.19), having trouble figuring out the best way to approach this. What I want to do is:
1. Make a cup shape with a post in the middle of the inside of the cup. The height of the post is lower than the rim of the cup.
2. At some other positions within the cup, add bosses that rise from the curved interior surface of the cup, to the same height as the central post.

I have made the cup with central post, from a sketch representing half of the vertical section through the post, and then revolving the sketch. I get the cup with the post; all good so far.
Then I have drawn a sketch on the top of the central post, so that the plane of the sketch is the same height as the post (the post has a flat top). On the sketch, I have drawn circles for the bosses.

Then, I'm stuck. I can't find a tool/method that will allow me to extrude (probably the wrong word) the bosses down to the inside of the cup.

I can project the outlines of the bosses onto the inside of the cup, but then cannot find a way to 'grow' these to exactly the same height as the central post (I can extrude them, but the option is a single-figure height and I don't know where this is measured from since the surface is curved).

Used Part Design and Part workbenches. I did get a dialogue box about using a Shape Binder, but don't know if I need that nor how to use it - for what I am trying to do.

Any suggestions? I probably need to adjust my work flow and thinking of how to tackle the problem, but if you don't know what you need to do, it is hard to imagine the correct steps in the correct sequence.

My approach is based on a scant familiarity with another CAD package, which (using the steps I was aiming for) looks like the attachment.
Cup with post and bosses.png
Cup with post and bosses.png (336.44 KiB) Viewed 913 times
Last edited by tony902 on Mon Feb 06, 2023 11:11 am, edited 1 time in total.
GeneFC
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Re: Best way to add boss up to a curved surface?

Post by GeneFC »

tony902 wrote: Sun Feb 05, 2023 9:46 pm
The simple method is to grow the bosses to some convenient height and chop them off with a sketch-then-pocket or some Boolean subtraction, or whatever, depending on the workbench you are using.

Gene
Bance
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Re: Best way to add boss up to a curved surface?

Post by Bance »

Ideally one would use the Pad 'up to face' option, but unfortunately that isn't working for concave surfaces.

Instead use a Pad from the flat and trim with a subtractive revolve (Groove.)
Attachments
Boss.FCStd
(319.53 KiB) Downloaded 10 times
mconsidine
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Re: Best way to add boss up to a curved surface?

Post by mconsidine »

Subtract one hemisphere from another, the former one having holes in it to the appropriate depths?
mconsidine
chrisb
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Re: Best way to add boss up to a curved surface?

Post by chrisb »

Bance wrote: Sun Feb 05, 2023 10:19 pm Ideally one would use the Pad 'up to face' option, but unfortunately that isn't working for concave surfaces.
"Up to face" works well, but here I prefer "To first", because it doesn't suffer from the topological naming problem.
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Bance
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Re: Best way to add boss up to a curved surface?

Post by Bance »

chrisb wrote: Mon Feb 06, 2023 4:44 am "Up to face" works well
I confess I didn't try it I was convinced it didn't work. :lol: :lol: :oops: :oops:
tony902
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Re: Best way to add boss up to a curved surface?

Post by tony902 »

Thank you all for your replies and suggestions, very quick too (overnight from here in UK).

I like the ideas, after playing around with the file supplied by Bance, I tried a similar method and it worked. A bit convoluted, I made the central post far taller than necessary, then padded a platform on top of it. Sketching the bosses on the underside of this platform and growing them down to the inside face of the cup worked well, then groove-removed the platform and the unwanted portions of the central post/bosses:
Cup with top.png
Cup with top.png (150.73 KiB) Viewed 600 times
This seems to work well, I can fillet around the join of the boss to the inside of the cup so it seems to be a solid object. I hope it doesn't fall apart in printing!
Thanks again, truly appreciated.
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Shalmeneser
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Re: Solved - Best way to add boss up to a curved surface?

Post by Shalmeneser »

:idea:

Provide your file.
Attachments
Annotation 2023-02-06 120952.jpg
Annotation 2023-02-06 120952.jpg (40.37 KiB) Viewed 573 times
Boss_Bance_SHALM.FCStd
(197.16 KiB) Downloaded 8 times
chrisb
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Re: Best way to add boss up to a curved surface?

Post by chrisb »

Bance wrote: Mon Feb 06, 2023 8:11 am I confess I didn't try it I was convinced it didn't work. :lol: :lol: :oops: :oops:
With all those issues with e.g. Thickness it can indeed be seen as unexpected that this works so well.

And here is my related, but nevertheless off topic wish: I would like to see an option "to n-th face" for pads and especially pockets, where I rather often need "Up to second".
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
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