Draw a sketch using external reference points

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Kikokou-san
Posts: 4
Joined: Thu Mar 08, 2018 12:45 pm

Draw a sketch using external reference points

Postby Kikokou-san » Thu Mar 08, 2018 12:53 pm

Hi all,

I have a problem I am stuck with since yesterday. I've searched and read / watch a lot of tutorials but cannot find out the answer.

I am trying to draw a sketch on a planar part (already designed). Should be simple right ? :lol:

This part already has some pockets on its surface, and some cuts on its edges.

The sketch mode is correctly opening when I try to draw a sketch on this surface, but if I try to draw a rectangle, I cannot snap to any point on this surface (for example, the angle of a square pocket, or an angular point of the edge of the surface). I tried the tool "Create an edge linked to an external geometry", this seems to get closer to what I want to do but this is only for edges, not for points..

I hope my problem is clear, if not I could provide a file.

Thanks in advance

Cheers,
chrisb
Posts: 24294
Joined: Tue Mar 17, 2015 9:14 am

Re: Draw a sketch using external reference points

Postby chrisb » Thu Mar 08, 2018 1:39 pm

You should always add your FreeCAD info to such questions, because the answer may depend on it - as is here the case. How to do that is described in the forum rules linked with the "IMPORTANT: ..." text above.

External geometry to which you are referring can reference points as well as lines. In 0.16 you can refer only to points and edges of the plane to which the sketch is attached. In 0.17 you can refer other edges and points as well, as long as they are in the same body. Other geometry has to be imported with a ShapeBinder, if you want to reference it.
Kikokou-san
Posts: 4
Joined: Thu Mar 08, 2018 12:45 pm

Re: Draw a sketch using external reference points

Postby Kikokou-san » Thu Mar 08, 2018 1:56 pm

Hi Chrisb,

Sorry for that.

Here are my infos :

OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.16.6712 (Git)
Build type: Release
Branch: releases/FreeCAD-0-16
Hash: da2d364457257a7a8c6fb2137cea12c45becd71a
Python version: 2.7.8
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 6.8.0.oce-0.17

The strange thing is that I cannot refer to points.. Only lines (edges). However those points are well in the plane to which the sketch is attached..

I will try again with a model created from scratch within FreeCad (because mine was imported as .STEP format) and advise..
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HarryGeier
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Location: Hof Germany

Re: Draw a sketch using external reference points

Postby HarryGeier » Thu Mar 08, 2018 2:13 pm

Just in case you fail with the imported geometry here is a workaround:

Create 2 construction lines . create 5 POINTS

fix the lines onto the selected edges from external geometry with 2 points which bind by POINT TO OBJECT constraint

Now fix Point 5 to the crossing of the lines and have the corner point.-.

..bit strange approach, but it may work.. i am not sure if we already had Datum lines in 0.16 ...which would solve the problem in .17
Kaum macht man´s richtig , gehts´s
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chrisb
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Re: Draw a sketch using external reference points

Postby chrisb » Thu Mar 08, 2018 5:05 pm

Kikokou-san wrote:
Thu Mar 08, 2018 1:56 pm
The strange thing is that I cannot refer to points.. Only lines (edges). However those points are well in the plane to which the sketch is attached..
Please upload your FreeCAD file.
HarryGeier wrote:
Thu Mar 08, 2018 2:13 pm
..bit strange approach, but it may work.. i am not sure if we already had Datum lines in 0.16 ...which would solve the problem in .17
Datum lines were introduced in 0.17.
Kikokou-san
Posts: 4
Joined: Thu Mar 08, 2018 12:45 pm

Re: Draw a sketch using external reference points

Postby Kikokou-san » Thu Mar 08, 2018 10:13 pm

OK, thanks, I finally managed to select points as well..

It is just that it was not obvious so I did not think it was possible (lines get highlighted when hovering but points not so much).

So I managed to do it if the reference point are in the same plane.

So now, I'm stuck with another problem...

What if the reference points I would like to refer to draw my sketch are within another plane / part ?

I tried drawing the sketch on the other part (on which are my reference points) and then apply the sketch to the face where I want to extrude but this completely mess the orientation of the sketche..

Thanks..
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HarryGeier
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Location: Hof Germany

Re: Draw a sketch using external reference points

Postby HarryGeier » Thu Mar 08, 2018 10:17 pm

Kikokou-san wrote:
Thu Mar 08, 2018 10:13 pm
OK, thanks, I finally managed to select points as well..

It is just that it was not obvious so I did not think it was possible (lines get highlighted when hovering but points not so much).

So I managed to do it if the reference point are in the same plane.

So now, I'm stuck with another problem...

What if the reference points I would like to refer to draw my sketch are within another plane / part ?

I tried drawing the sketch on the other part (on which are my reference points) and then apply the sketch to the face where I want to extrude but this completely mess the orientation of the sketche..

Thanks..
..i honestly suggest.. switch to .17

there you can easily do that via "shapebinder"
Kaum macht man´s richtig , gehts´s
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Kikokou-san
Posts: 4
Joined: Thu Mar 08, 2018 12:45 pm

Re: Draw a sketch using external reference points

Postby Kikokou-san » Thu Mar 08, 2018 10:25 pm

Hi Harry,

I have to admit I tried this afternoon and.. The first face I selected to draw a sketch on it warned me with several error messages that it was not a solid or so on.. So I did not try further as I understood the workflow are quite different between both..

But maybe I'll reconsider it..
chrisb
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Joined: Tue Mar 17, 2015 9:14 am

Re: Draw a sketch using external reference points

Postby chrisb » Thu Mar 08, 2018 11:05 pm

Kikokou-san wrote:
Thu Mar 08, 2018 10:25 pm
I have to admit I tried this afternoon and.. The first face I selected to draw a sketch on it warned me with several error messages that it was not a solid or so on.. So I did not try further as I understood the workflow are quite different between both..

But maybe I'll reconsider it..
The main difference is, that you have to stay within one body when working with PartDesign in 0.17. If you want to reference geometric elements from other objects you have to import a ShapeBinder which serves as a proxy for external objects.
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HarryGeier
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Location: Hof Germany

Re: Draw a sketch using external reference points

Postby HarryGeier » Fri Mar 09, 2018 6:51 am

..i tell you..

when i switched to 0.17 , in it´s early days... i got MAD MAD MAD about this... It took me a while to understand what a "active body" is and how it all plays together..
Meanwhile i cannot imagine how it was possible to work with 0.16 at all..

The Key is to understand BODY and the fact that each BODY has its "own world" ,... it´´s like C vs C++ with object orientation
and remember to keep an eye on which BODY is the active one.. ( blue background of Body name )
Kaum macht man´s richtig , gehts´s
My Video Tutorials on Youtube: https://www.youtube.com/channel/UCoe3B ... p8Q/videos
My FreeCAD Stuff on Hidrive: https://my.hidrive.com/share/qr3l1yddy6#$/