How to use external geometry in parametric design

[microelly2]

Today we have modeled a lego stone.

lego.png (83.9 KiB) Viewed 1570 times

what is lego - http://www.infoskript.de/inf-schule/ind ... rechnungen
How to get a good parametric design?

The story:
I have used some multitransform features to put the right count of tooths on the upper side and the cylinders in the bottom side on the required positions
Starting with the 2 x 4 stone I now want to get a 3 x 10 stone.

3x10-lego.jpg (106.13 KiB) Viewed 1570 times

When I have a sketch on top of a multitransform feature with constraints(here: the bottom cylinders must fit the tooths of the next stone) and I change the counts in the mt-feature then I loose the bindings to the right external geometry objects because the numbers of faces and edges change.

what are good constraints in such a case?
It seems to me that only hard position (constrain lock), hard coded angles, distances of points work.
Soft constraints like tangent, parallel ... do not work because the external geometries move or are lost.
I wanted to avoid hard coding. Is it possible to have some anchor geometry trough the levels of design
where I can bind my new features and which do not change when the other geometry changes - can I create something like a helper face, edge which is always "face1" or "edge1"

Here is the starting model. When you change the occurences value in the " MultiTransform 8 Zaehne" the upper sketches are torned.

I hope that somebody has a nice idea.
thanks in advance.

[NormandC]

Today we have modeled a lego stone.

In English we call it a brick, not stone.

Is it possible to have some anchor geometry trough the levels of design
where I can bind my new features and which do not change when the other geometry changes - can I create something like a helper face, edge which is always "face1" or "edge1"

It's not possible AFAIK.

But the upcoming changes to Part Design along with the Body container will allow squeleton modeling, and I suspect that using "master sketches" for external geometry in other sketches will in part solve the current problems.

See this tutorial for such a workflow: http://freecadweb.org/wiki/index.php?ti ... Tutorial_I
Please note this tutorial only works with a special development branch, not with the current verison of FreeCAD.