LCS and datum plane placement tricks

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drmacro
Posts: 2575
Joined: Sun Mar 02, 2014 4:35 pm

LCS and datum plane placement tricks

Postby drmacro » Fri Apr 17, 2020 3:55 pm

Working on this exercise and I found placement of the plane to create surface A to be rather tricky.

I did it by forcing an edge in the first pad buy breaking a sketch line into two segments.

I love see how other would approach modeling this item:
Fig_8-49.jpg
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Fig_8-49-2.png
Fig_8-49-2.png (50.62 KiB) Viewed 447 times
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Fig_8-49-2.FCStd
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Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."

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kisolre
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Re: LCS and datum plane placement tricks

Postby kisolre » Fri Apr 17, 2020 7:15 pm

Create a full topview sketch1, pad. Pocket the tail. Create a sketch at pad height, carboncopy sketch1 as construction geometry, create edge between A and B. Map sketch to that edge, cut front tip at 105 deg.
drmacro
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Re: LCS and datum plane placement tricks

Postby drmacro » Sat Apr 18, 2020 1:54 pm

kisolre wrote:
Fri Apr 17, 2020 7:15 pm
Create a full topview sketch1, pad. Pocket the tail. Create a sketch at pad height, carboncopy sketch1 as construction geometry, create edge between A and B. Map sketch to that edge, cut front tip at 105 deg.
Thanks.
I tried this. The attached file is my attempt. And it does get the job done.

But, the CC'd sketch geometry (in Sketch003) is now is used only as the source of the attachment. Correct?
Attachments
Fig_8-49-3.FCStd
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Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."

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Bance
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Re: LCS and datum plane placement tricks

Postby Bance » Sat Apr 18, 2020 3:10 pm

I just attached the DP to the base sketch with a rotation offset.
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soidworksToolholder.FCStd
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kisolre
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Re: LCS and datum plane placement tricks

Postby kisolre » Sat Apr 18, 2020 3:44 pm

I would not use datum entities, because there are not multiple items to map to them and mapping is simple. For that front cut sketch use minimum edges to minimize computation difficulty.
Did you forget the round of the tail?
Here are my modifications to your file:
.
Fig_8-49-3_kiss.JPG
Fig_8-49-3_kiss.JPG (91.66 KiB) Viewed 370 times
.
Funny thing is that I tried to use the top sketch as base for a Hole feature but this failed because it had also straight edges as normal geometry. If I remember correctly this worked in the past. Could anyone confirm?

OS: Windows 8.1 (6.3)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.20477 (Git)
Build type: Release
Branch: master
Hash: 7d8ab175a68e476427e6e337fe3099b52da49dc8
Python version: 3.6.8
Qt version: 5.12.1
Coin version: 4.0.0a
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Locale: Bulgarian/Bulgaria (bg_BG)
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drmacro
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Re: LCS and datum plane placement tricks

Postby drmacro » Sat Apr 18, 2020 5:05 pm

kisolre wrote:
Sat Apr 18, 2020 3:44 pm
I would not use datum entities, because there are not multiple items to map to them and mapping is simple. For that front cut sketch use minimum edges to minimize computation difficulty.
I see you changed the duplicate geometry in the CC'd sketch to construction lines. Just because or does that help computation as well?
Did you forget the round of the tail?
Nope, just being lazy. I had it in earlier versions... :oops:
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papyblaise
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Re: LCS and datum plane placement tricks

Postby papyblaise » Sat Apr 18, 2020 5:45 pm

Mine
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porte outil.PNG
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kisolre
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Re: LCS and datum plane placement tricks

Postby kisolre » Sat Apr 18, 2020 5:59 pm

drmacro wrote:
Sat Apr 18, 2020 5:05 pm
Just because or does that help computation as well?
To minimize the clutter when not editing the sketch. Only edges needed outside the sketch edit mode were left. Circles for the Hole feature, which failed, edges for sketch mapping.
freedman
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Re: LCS and datum plane placement tricks

Postby freedman » Sun Apr 19, 2020 8:38 pm

I like the kisolre design but instead I would have used a top datum plane for the threaded holes and cutter holder square cutout, I see these two features as dependent on each other. If someone later had to modify the model they would be glad these items were on a plane and sketched from above IMO.

This is a fun model, many different approaches. :)
drmacro
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Re: LCS and datum plane placement tricks

Postby drmacro » Mon Apr 20, 2020 1:56 pm

freedman wrote:
Sun Apr 19, 2020 8:38 pm

This is a fun model, many different approaches. :)
If you like that one, here is another:

https://forum.freecadweb.org/viewtopic.php?f=3&t=45487
Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."

My beginners, written treatise: Learning FreeCAD