How to change my workflow to get better editability

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AndreKR
Posts: 27
Joined: Thu Nov 30, 2017 9:47 am

How to change my workflow to get better editability

Postby AndreKR » Sun Apr 15, 2018 10:11 pm

For this example, let's take a body like this:

2018-04-15_2355.png
2018-04-15_2355.png (3.08 KiB) Viewed 376 times

Now I want to pocket the top 5 mm of the protruding part, to get something like this:

2018-04-15_2356.png
2018-04-15_2356.png (2.51 KiB) Viewed 376 times

What I usually do is, I select that face:

2018-04-16_0005.png
2018-04-16_0005.png (2.23 KiB) Viewed 376 times

Then I fetch my reference point with the external geometry button:

2018-04-16_0007.png
2018-04-16_0007.png (1.34 KiB) Viewed 376 times
2018-04-15_2350.png
2018-04-15_2350.png (6.38 KiB) Viewed 376 times

(continuation in next post because I can only upload 5 images)
Last edited by AndreKR on Sun Apr 15, 2018 10:21 pm, edited 3 times in total.
AndreKR
Posts: 27
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Re: How to change my workflow to get better editability

Postby AndreKR » Sun Apr 15, 2018 10:20 pm

And create my sketch relativ to that geometry:

2018-04-15_2351.png
2018-04-15_2351.png (8.52 KiB) Viewed 374 times

Which leads to the desired result:

2018-04-15_2356.png
2018-04-15_2356.png (2.51 KiB) Viewed 372 times

So far this workflow is very conventient and fast.

Unfortunately it leads to two problems:

1. When I change the parameters of earlier features, my body breaks, because the sketch isn't actually referenced to that external geometry, but rather to the origin of the whole body. See what happens when I decrease the length of the Pad:

2018-04-15_2354.png
2018-04-15_2354.png (2.95 KiB) Viewed 374 times

2. When I add faces to earlier features, for example by removing a Fillet that I created to early (or in this example by adding a fillet) the later features become referenced to completely different faces:

2018-04-15_2358.png
2018-04-15_2358.png (3.89 KiB) Viewed 374 times
That hole down there is the sketch from the Pocket seen earlier - it has moved to the other face. By itself this is understandable, because the number of faces in the earlier feature changes.

Using the new Attachment editor in 0.17 (or even the plain old Map-sketch-to-face button) it should be easy to correct. However, there seems to be no way to re-map the external geometry that I was referencing my sketch on, and so the sketch becomes broken and I have to re-do most of the constraints:

2018-04-16_0000.png
2018-04-16_0000.png (32.71 KiB) Viewed 374 times

What should I change in my workflow to make such later edits easier?
chrisb
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Re: How to change my workflow to get better editability

Postby chrisb » Sun Apr 15, 2018 10:49 pm

You can use the "Validate sketch" tool fromPart Design workbench and delete all references to external geometry, then you can remap your sketch edit it, remove the old external references and add new ones.

In the Documentation of PartDesign WorkbenchFeature_editing#Advice_for_creating_stable_models there are some hints, how to create a robust model. Please read the paragraph "Advice for creating stable models".
triplus
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Re: How to change my workflow to get better editability

Postby triplus » Sun Apr 15, 2018 11:14 pm

AndreKR wrote:
Sun Apr 15, 2018 10:20 pm
1. When I change the parameters of earlier features, my body breaks, because the sketch isn't actually referenced to that external geometry, but rather to the origin of the whole body. See what happens when I decrease the length of the Pad:
I can confirm the issue. But i am guessing this likely should work as expected (like it did in FreeCAD 0.16). Therefore i am guessing there is a bug involved somewhere.
2. When I add faces to earlier features, for example by removing a Fillet that I created to early (or in this example by adding a fillet) the later features become referenced to completely different faces:
This is normal and to be expected. Going back in the design history to add/remove geometry will produce issues for features added after. This is what "topological naming" ongoing projects will try to improve in the future. Being able to go back in design history and by adding/removing geometry. To experience less issues with the features added after.
AndreKR
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Re: How to change my workflow to get better editability

Postby AndreKR » Sun Apr 15, 2018 11:33 pm

In reply to chrisb's answer:

I have to admit, that is not entirely the advice I was hoping for.

Indeed the idea of having three "master sketches" that serve as the only reference in the body is something I will definitely try.

But still, the new Attachment/Map Mode editor makes it super easy to map a sketch to a face. Now if only the origin of that sketch would depend on that face, everything would work out. (It doesn't even have to be a specific point of the face, usually any point of that face would already be helpful.)

Referencing previous geometry is great because often I don't know the position of a feature relative to the origin:
- I might say "put the light switch 10 cm left of the door" and not "put the light switch 350 cm from the origin of the room".
- When I measure a distance using calipers, I can only measure it relative to something close by.

Sure, in most cases I could calculate the distance relative to the origin, but I feel like that is something the software should do for me.
AndreKR
Posts: 27
Joined: Thu Nov 30, 2017 9:47 am

Re: How to change my workflow to get better editability

Postby AndreKR » Sun Apr 15, 2018 11:38 pm

triplus wrote:
Sun Apr 15, 2018 11:14 pm
Going back in the design history to add/remove geometry will produce issues for features added after. This is what "topological naming" ongoing projects will try to improve in the future.
I don't mind re-mapping the face when I add/remove faces. After all it's difficult to define what constitutes "the same face" after you have changed the geometry.
But sure, if this can be solved by using named faces or something, why not do that as well.
AndreKR
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Re: How to change my workflow to get better editability

Postby AndreKR » Mon Apr 16, 2018 12:46 am

One thing I don't understand from the wiki article:
you need to stop mapping sketches to faces - entirely
If I do that, how do I make pockets starting from a face?
chrisb
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Re: How to change my workflow to get better editability

Postby chrisb » Mon Apr 16, 2018 4:54 am

AndreKR wrote:
Mon Apr 16, 2018 12:46 am
One thing I don't understand from the wiki article:
you need to stop mapping sketches to faces - entirely
If I do that, how do I make pockets starting from a face?
The master sketch is not the only technique mentioned to make models robust, and sometimes it might be too much effort to work around mapping to faces.
But in most cases you can use a DatumPlane which references Sketches and on that DatumPlane you can attach a Sketch for creating a pocket. And again, external references which are used in that sketch should use other sketches instead of referencing edges or vertices of a solid.
freecad-heini-1
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Re: How to change my workflow to get better editability

Postby freecad-heini-1 » Mon Apr 16, 2018 5:41 am

chrisb wrote:
Mon Apr 16, 2018 4:54 am
The master sketch is not the only technique mentioned to make models robust, and sometimes it might be too much effort to work around mapping to faces.
But in most cases you can use a DatumPlane which references Sketches and on that DatumPlane you can attach a Sketch for creating a pocket. And again, external references which are used in that sketch should use other sketches instead of referencing edges or vertices of a solid.
The use of a mastersketch is just one piece of the cake, the next are datum-features, but not referenced to shape. Next technique is to use a shape without fillets and chamfers. It could be a pad or part-extrude (as shell), pad parametric downgraded to shell (Lattice2-workbench). Set this shape on top of every design as a skeleton model, based on a master sketch. It will not break and has no problems with topo naming and you can use all faces, edges and vertices as reference for other objects. Copy them to the body you want. If you change the mastersketch and the skeleton modell all dependent geometrie will follow full parametric.
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HarryGeier
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Re: How to change my workflow to get better editability

Postby HarryGeier » Mon Apr 16, 2018 6:05 am

I think the problem in that case is the reference you take for the external ref.

Look at my version, here you can move and change the small block without breaking . I reference the cutout perpendicular , so the referenced line does not dissapear completely during calculations after moving the previous sketch.

I reference at the top line along of the second block, as you can see.,
Image

it even survives a move out of scope, just needs a resync in the sketch to find the reference again.

I think it has much to do with the plane where the referenced element is, after a while you start to know,
what will and what won´t survive.

Best is allways, to reference to points which will not move. Also try to reference back in history as far as possible...i.e. to a Master Sketch


...later i found an easy approach...reference to the line that is fixed and not a part of the pocket itself...

( the line between the 2 yellow datum points , which you could also use )
2018-04-16 08_28_20-FreeCAD.png
2018-04-16 08_28_20-FreeCAD.png (9.67 KiB) Viewed 313 times
that also survives , including weird movements ( needs recalculation sometimes )
Attachments
test.fcstd
(23.18 KiB) Downloaded 3 times
Last edited by HarryGeier on Mon Apr 16, 2018 6:33 am, edited 1 time in total.
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