You are right with your assumptions about the idea of a master sketch. Referencing them works like other references in Sketcher with Sketcher External.
First, Thanks for the answer. The first link was very informative.ppemawm wrote: ↑Fri Jun 01, 2018 12:45 amExamples:
https://forum.freecadweb.org/viewtopic. ... 00#p227968
https://forum.freecadweb.org/viewtopic. ... 91#p232277
https://forum.freecadweb.org/viewtopic. ... 04#p217871
A master sketch(es) should be as simple as possible in order to capture the key design intent. Once you reference a master sketch using External Reference in another sketch or link to it via a Shapebinder in another body by sketch Attachment properties, you usually cannot make any significant changes (add or subtract vertices or edges) to the master or it may break the model. Using master sketches requires that you think through how you will create the model before you start.
The restrictions are usually the result of the tree relationship between the different objects. And I don't pretend to understand the bowels of FC in details anyway. That said looking at the external tool restrictions:fusan wrote: ↑Fri Jun 01, 2018 7:43 pmSince the idea with a master sketch is to reference other sketches to it to make them easier to create, I don't get why it is so inflexible.
To me it would be a great to only change the master sketch and all sketches referenced to it would update to.
Maybe I'm missing something here.
I wondered if I could "clone" an external sketch and put the sketch inside multiple bodies to use it with external and it worksOnly edges and vertices from objects from same coordinate system are allowed.
That is, the sketch and the object must be in same Body, or in same Part, or both outside of any Parts and Bodies.
You don't use the clone, you use a ShapeBinder instead. It is kind of a proxy for the original element.
It is quite flexible and any sketch linked to it will update changes. But, you generally cannot change the number of elements in the master sketch once it is linked or it may break the model. You can change dimensions and constraints, however, and the linked sketches will update.
I use a Shapebinder rather than a Clone. A BaseFeature is intended to be used with solids from other workbenches for the beginning feature of a PartDesign>Body.
And even if the model breaks, because you had to add something to the structure, it seems to be easier to repair than a model attached to faces and referencing edges and vertices; probably because it stays 2D and the references or attachment faces don't hide in the smalles corners of a 3D object.ppemawm wrote: ↑Fri Jun 01, 2018 9:50 pmIt is quite flexible and any sketch linked to it will update changes. But, you generally cannot change the number of elements in the master sketch once it is linked or it may break the model. You can change dimensions and constraints, however, and the linked sketches will update.
Thanks ppemawm for the clear explanations, looking at your screen captures on your amazing models was not obvious how the shape-binders would be used. I've redone the same example using shape-binders (joined).ppemawm wrote: ↑Fri Jun 01, 2018 9:50 pmFor example, you can make a master sketch of all the key vertices of the moving parts in an engine. Then, as you begin modelling each moving body, create a Shapebinder of the master sketch for reference in each body. Attach sketches to the Shapebinder at the appropriate location using the MapMode to create the Body. You can use external geometry links in the sketch if needed. Once the body is completed you can go back to the master sketch and change the main variable, such as the crankshaft angle, and all of the bodies will move to their new location. This is useful for animating and checking clearances or interferences in the engine as the crankshaft rotates.
I use a skeleton sketch as the master for location only. The body sketches are attached to a shapebinder of the master to create the detail geometry. If that is suboptimal and means a second or two greater compute time that's OK with me. I am bit old school greybeard that promotes keeping it simple.
No, yes, yes. I have a simple macro to move the master sketch variable angle 0-360 deg to check the robustness of the constraints and for interference checks or I simply change the angle constraint manually in the Property panel for a quick check.
I have a file of a simple planetary gear set in PartDesign using an articulating master sketch which may give you some ideas. It is too large for the Forum but can be put on Dropbox if you are interested.dbecad wrote: ↑Sat Jun 02, 2018 12:23 amMy current quest is to design a simple mechanical watch movement and I'm not completely satisfied with my current way of modeling gear trains, where the distance between shafts and positions of said shaft should be parametric. Also animating it after would be a nice plus...