Thickness equivalent for a sketch?

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Joined: Sat May 01, 2021 3:09 pm

Thickness equivalent for a sketch?

Postby hotsnail » Sat May 01, 2021 3:27 pm

Hello guys,

I am new to FreeCad. I am now learning the ins and outs of parametric design. One of my projects is to make an adapter that starts off as a sleeve of a photographic flash, goes on to become projection slide holder and end with a lens mount. I want to use the flash to project slides on to a wall.

So I photographed the front of the flash and traced a perimeter. I did a couple of 3d prints to fine adjust so it fits snuggly. To print the test sleeves I used pad to create a solid that resembles the flash and then used "thickness" to create a wall that wraps around. This worked great.

Now I want to loft from that flash sleeve sketch to the slide holder sketch and then to the round lens mount sketch. The problem is my sketch for the flash has only one contour. Is there a way to autogenerate a second contour such that it is same shape and couple outside of the contour I got?

I am thinking something like the "Thickness" function both for sketch instead of solid. I will probably just draw an outline but woudl love to have parametric way to set the "thickness" of the sleeve wall

Alternatively I thought I can try somehow making a loft from the face of the "thickness" solid instead of a sketch if that is possible

OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.4 (GitTag)
Build type: Release
Branch: releases/FreeCAD-0-18
Hash: 980bf9060e28555fecd9e3462f68ca74007b70f8
Python version: 3.6.6
Qt version: 5.6.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: Bulgarian/Bulgaria (bg_BG)
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Re: Thickness equivalent for a sketch?

Postby chrisb » Sat May 01, 2021 5:10 pm

Hi and welcome to the forum!

First of all you should upgrade to a current 0.19 or 0.20 version.

I don't quite understand what you want, but what you have done is already wrong, as can be seen by the red arrow in the dependency graph:
SnipScreenshot-1eae52.png (27.24 KiB) Viewed 168 times
You must not use a sketch which lives inside of a body outside of that body.

To get an offset from a sketch you can use Part workbench's 2D offset tool.
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Posts: 2
Joined: Sat May 01, 2021 3:09 pm

Re: Thickness equivalent for a sketch?

Postby hotsnail » Thu May 06, 2021 11:21 am

Attached is what I tried to do.

The PartOffset2D did part of the job. It creates a new object with the expected geometry i.e. outline of a sketched figure with defined offset.

It is not usable in "Part Design" to power the Loft tool though. I had to go through few more hoops to turn the Offset2D into sketch and fuse with the initial sketch. Here are my steps.

1. Select the sketch you want to create outline for
2. Open the "Part" workbench
3. From "Part" menu select "2D Offset..."
4. Input the desired thickness in "Offset". Depending on your design play with the other parameters and click "Ok"
5. Select the "Offset2D" object that was just created
6. Set a view from the top (precisely from the top i.e. 90 degree). I literally used "top" as my sketch is in the XY plane. Next we convert the offset to sketch
7. Open "Draft" workbench
8. From "Modification" menu select "Shape 2D View" - this will create "Draft" that is projection of the "Offset2D".
9. Check that the newly created "Shape2DView" object is selected on the left
10. From "Modification" menu select "Draft to Sketch"
11. Drag the newly created sketch inside your "Body"
12. In the "Data" view set support to a plane of your choosing e.g. "XY_Plane" then on MapMode select "Plane face"
13. Open the Sketch by double clicking it
14. From "Sketch" menu, "Sketch Geometries" sub menu select "Carbon Copy" and click on a segment of your original sketch to bring it into the new sketch.

This is it all done you have a sketch with "offset" from original sketch that is useful in loft or pad tool.

You can delete all the extra objects.

The big downside of this solution is that one looses the the parametric part of FreeCad. Makes you wonder if using something simpler from the start would have paid off given that you can no longer update parameters of your project to fit new constraints e.g. thicker walls.....

I hope these steps help other people. There are plenty of discussions about the missing Offset function in Sketcher workbench. This seems the be much desired feature. I hope this soon finds place in FreeCad.
flash v2.FCStd
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