datum point on a middle of a edge - how to?

[m.cavallerin]

Hi,

I would like to create a datum point on the middle of the edge of the green highlighted edge.
The mapping options don't allow to select the middle of the edge.
What I would like to obtain is a plane like shown, but that change position according to the change of the radius.
(To obtain the plane I put an offset manually).

I thought to use Draft, but maybe I'm not expert with this WB and any entity I add outside PartDesign become a reference body: this is a solution i dislike as it causes the feature tree to become unreadable...but if it is the only solution

Any suggestion?

Thanks in advance

Michele

OS: Linux Mint 19.3 (X-Cinnamon/cinnamon)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.
Build type: Release
Python version: 3.6.9
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedStates (en_US)

[chrisb]

Move to Help forum. This is not a PartDesign development question. It may get more attention here.

[chrisb]

I guess you could do something with additional Datum geometry in XZ-plane. I went a different way and used an expression instead to offset the DatumPlane with the radius.

[chrisb]

I took it as an exercise, because I have by far not mastered Datum geometry yet. Here is a solution of what I talked above with a DatumPoint on the middle of the radius. It uses an additional DatumLine.

[chrisb]

And here is my favourite:
- attach the DatumPlane with "Normal to edge" to the Sketch's arc and
- turn it around y-axis by 90° which makes it tangent
- confirm
- set MapPath to 0.5 which moves it to the middle of the arc.

[papyblaise]

I simplify your drawing to include the 2 holes in the 1st sketch , your part is more robust (in Fc) , any risque to falldown with rename of toponoming
you had the inteligent to place the center of the circle in XOY , a Datum plan is not nessairy

[openBrain]

And here is my favourite:
- attach the DatumPlane with "Normal to edge" to the Sketch's arc and
- turn it around y-axis by 90° which makes it tangent
- confirm
- set MapPath to 0.5 which moves it to the middle of the arc.

I was thinking about this that IIRC already was discussed on the forum ... And I'm happy I don't have to search back.

EDIT : just notice that you can also refer directly to the edge (instead of the 2 first steps) and choose a 'Frenet TB' mode. The rest of the process is same.

[mario52]

hi

try Macro_WorkFeatures Points > Line center

Macro_FC_Convert_Lines



mario

[m.cavallerin]

https://forum.freecadweb.org/viewtopic. ... 56#p366456

Sorry for double thread on the forum, but I hadn't any notification on my profile panel that post has been moved here, maybe a problem with my settings

In any case:

I simplify your drawing to include the 2 holes in the 1st sketch , your part is more robust (in Fc) , any risque to falldown with rename of toponoming
you had the inteligent to place the center of the circle in XOY , a Datum plan is not nessairy

And here is my favourite:
- attach the DatumPlane with "Normal to edge" to the Sketch's arc and
- turn it around y-axis by 90° which makes it tangent
- confirm
- set MapPath to 0.5 which moves it to the middle of the arc.

both solutions are great.
As I already reported on Italian forum:
1) make a sktech with a line connecting center of arc and the arc
2) create an angular dimension
3) exit the sketch and make a datum plane normal to line and passing through the vetex of the line on the arc

now you can change the angle of the plane that is tangent to the arc by the sketch.

The bad news is that you have to define a sketch, but the good news is that you can set an offset on the z-direction so you can make a tangent plane to an arc, driven by an angular dimension and offset it to a specific distance.
Is there a way to make it by freecad mapping options? It's quite hard to look for help on documentation..

Screenshot from 2020-02-06 03-25-55.png (61.1 KiB) Viewed 1343 times

[m.cavallerin]

I simplify your drawing to include the 2 holes in the 1st sketch , your part is more robust (in Fc) , any risque to falldown with rename of toponoming
you had the inteligent to place the center of the circle in XOY , a Datum plan is not nessairy

Thanks, but I disagree, as the mirror feature I added refer to absolute planes and topological names does not change ever.
I agree with your suggestion if you use a plane defined inside the geometry.
But normally even on commercial software you can face the same problem-
My golden rule is that if you have symmetry on a model, you have to sketch and model symmetrically so any function and dimension (inside sketches), could be referred to this absolute entities that will never change their name, that's make it a robust way to model.
Other benefits is that feature tree is more readable to other users using it, because when you find a mirror feature you already know there is a symmetry on the model.
These are only POV about modelling...not to be misunderstood with the porno category...