Problem with sketch position. Help is wanted

Post here for help on using FreeCAD's graphical user interface (GUI).
Forum rules
and Helpful information
IMPORTANT: Please click here and read this first, before asking for help

Also, be nice to others! Read the FreeCAD code of conduct!
borei
Posts: 5
Joined: Wed Jul 21, 2021 3:01 am

Problem with sketch position. Help is wanted

Postby borei » Wed Jul 21, 2021 3:12 am

Hi All,
Im beginner with FreeCAD. First of all HUGE thank you for such product !
I've got some issue with sketch placement. Im trying to move my sketch to new position (using rotation around Y-axis), but freecad is shifting sketch a bit, so i can't apply it to generate final body. I have attached my mode model file.
There is side-rib-sketch, im trying to rotate it -12 deg around y-axis, after rotation is completed it's got shifted towards axis of rotation, but im expecting that it should be inside "segment-shell". Can't find where is the problem.
Attachments
impeller-segment-v3.FCStd
(200.75 KiB) Downloaded 12 times
User avatar
Shalmeneser
Posts: 705
Joined: Wed Dec 23, 2020 12:04 am

Re: Problem with sketch position. Help is wanted

Postby Shalmeneser » Wed Jul 21, 2021 8:09 am

Beware, placement axis and general axis are not always the same.
Hand-drawing ?
chrisb
Posts: 35957
Joined: Tue Mar 17, 2015 9:14 am

Re: Problem with sketch position. Help is wanted

Postby chrisb » Wed Jul 21, 2021 9:09 am

Confusion is sometimes caused by the fact, that the rotation is carried out first and then the translations in the new direction.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
kisolre
Posts: 3205
Joined: Wed Nov 21, 2018 1:13 pm

Re: Problem with sketch position. Help is wanted

Postby kisolre » Wed Jul 21, 2021 9:16 am

What moves is not the sketch but its geometry. This happens because all of it is linked to projected external geometry points. They are always projected normal to the sketch so with the changing angle their projections move as well.
GeneFC
Posts: 2307
Joined: Sat Mar 19, 2016 3:36 pm
Location: Punta Gorda, FL

Re: Problem with sketch position. Help is wanted

Postby GeneFC » Wed Jul 21, 2021 2:46 pm

I believe the sketch is moving exactly as requested. Namely the rotation is occuring around the *origin* of the sketch.

The fact that all of the visible sketch details are well off-axis means that it will always appear there is translation in addition to rotation.

Think of an object on the rim of a wheel. If you rotate the entire wheel on its axle the object on the rim will undergo both rotation and translation.

Gene
User avatar
Shalmeneser
Posts: 705
Joined: Wed Dec 23, 2020 12:04 am

Re: Problem with sketch position. Help is wanted

Postby Shalmeneser » Wed Jul 21, 2021 3:15 pm

Circles around the 3 axis.
Attachments
Capture du 2021-07-21 17-14-20.png
Capture du 2021-07-21 17-14-20.png (42.74 KiB) Viewed 280 times
borei
Posts: 5
Joined: Wed Jul 21, 2021 3:01 am

Re: Problem with sketch position. Help is wanted

Postby borei » Thu Jul 22, 2021 4:16 am

looks like i don't understand how does geom transformation works. On the following screenshot i created sketch on YZ plane and moving it in Y direction 450 mm, but it was moved in Z direction. Why ???
Attachments
shot-2021-07-21_21-16-08.jpg
shot-2021-07-21_21-16-08.jpg (740 KiB) Viewed 248 times
borei
Posts: 5
Joined: Wed Jul 21, 2021 3:01 am

Re: Problem with sketch position. Help is wanted

Postby borei » Thu Jul 22, 2021 4:24 am

Shalmeneser wrote: Wed Jul 21, 2021 8:09 am Beware, placement axis and general axis are not always the same.
Hand-drawing ?
yep, it's hand-drawing. need to build "first approach" model, based only on the common sense.
borei
Posts: 5
Joined: Wed Jul 21, 2021 3:01 am

Re: Problem with sketch position. Help is wanted

Postby borei » Thu Jul 22, 2021 4:27 am

kisolre wrote: Wed Jul 21, 2021 9:16 am What moves is not the sketch but its geometry. This happens because all of it is linked to projected external geometry points. They are always projected normal to the sketch so with the changing angle their projections move as well.
so rotating 90 deg - will it disappear completely ?
borei
Posts: 5
Joined: Wed Jul 21, 2021 3:01 am

Re: Problem with sketch position. Help is wanted

Postby borei » Thu Jul 22, 2021 4:37 am

kisolre wrote: Wed Jul 21, 2021 9:16 am What moves is not the sketch but its geometry. This happens because all of it is linked to projected external geometry points. They are always projected normal to the sketch so with the changing angle their projections move as well.
looks like it's the reason.
Then question would be - how to rotate sketch with external geometry ?