Missing origo in sketch and how to fix it

[OrjanB]

Alibre Design v25

During making a part:
Sketching on one of the original planes I make a rectangle by center, constrained to origo by default, dimension it and extrude to a flat part.
I then go on working on this part: Making holes and cuts by use of new sketches.
The original rectangle is untouched.
The part is inserted in an assembly together with other parts.
During the work the part is opened several times for changes in design.
I then discover that the rectangle mentioned above is not fixed anymore, the origo has gone and the rectangle is moving freely in the sketch.
I can snap to the center of rectangle and move it, but there is no origo anymore to attach to.

Anyone experienced the same?

My solution after annoying experimenting:
On the same original plane as the problem-sketch I make a new sketch:
A circle with center connected to origo.
In the browser this sketch is moved to the top so it is placed before the faulty sketch.
I open the problem-sketch for editing.
The center-node (origo) of the circle-sketch is projected to the problem-sketch.
Now I can constrain the center of rectangle in the problem-sketch to this node.
Problem solved.

Is this an error in Alibre or have I missed something?

One strange thing is also that I now can delete the sketch with the circle - the projected node still exists in correct position.

Concerning rectangle by center:
When first making it, it is kept horisontal/vertikal by default, but after dimensioning it rotates and I have to constrain it manually. Should not behave like that.

Orjan

 

[HaroldL]

Concerning rectangle by center:

Rectangle by Center only has Perpendicular constraints, you need to add a Horizontal or Vertical constraint if you need them. Otherwise you can rotated it to any angle that may be necessary.

Rectangle as sketched and dimensioned:


Rectangle after adding a Vertical constraint:

 

[OrjanB]

My point is that when first making the rectangle it is horizontal/vertical locked and that it after dimensioning can be rotated.
This can, in my opinion, generate error because I intuitively expect it to keep orientation after dimensioning.
If the rotate angle is very small it may be overlooked and problems may occur later.
Manually adding the constraint is of course no problem, but in my opinion not logical.
Orjan

 

[idslk]

Hello Orjan,

This can, in my opinion, generate error because I intuitively expect it to keep orientation after dimensioning.

if you initially create an centred rectangle it isn't locked horizontal or vertical! See color code (in my case red) for Magnitude/Position undefined!



the symbols in red box 1 show midconstraint and the symbols in the boxes 2 are showing the 2 two lines meeting are rectangular. Nothing more.
If you add the dimensions to the lines the rectangle has left one degree of freedom! this could be used to turn the rectangle around the origin and you can add a third dimension to make it fully defined. See color code (in my case) Gray for fully defined! (or use a constraint like harold)


Regards
Stefan

 

[HaroldL]

My point is that when first making the rectangle it is horizontal/vertical locked and that it after dimensioning can be rotated.
This can, in my opinion, generate error because I intuitively expect it to keep orientation after dimensioning.
If the rotate angle is very small it may be overlooked and problems may occur later.
Manually adding the constraint is of course no problem, but in my opinion not logical.
Orjan

So now you have two examples showing that it is not locked horizontal/vertical. IF you have sketch constraints turned on look at the rectangle after you create it. You will not see a vertical or horizontal constraint symbol - only perpendicular between at the corners. You need to manually add a horizontal or vertical constraint if you want it to remain in that orientation.

When Rectangle by Center was first introduced I reported to support that it was not constrained horizontal or vertical. I was told that this was by design so it could be rotated to any angle needed by the designer.

 

[OrjanB]

As you both point out, the active constraints when making the rectangle first time is visible: Perpendicular constraints and only these.
Neverthless, in the beginning the rectangle is horisontal/vertical locked despite lack of horisontal/vertical constraints.
This is what can make confusion, but no problem when you are aware of it.
And as Harold points out: This give the designer more possibillities when designing - I agree to that.

I notice that there is no comments to the main theme of this thread: Loss of Origo.
Means that it is not a general problem,..............(?)

Orjan

 

[HaroldL]

I notice that there is no comments to the main theme of this thread: Loss of Origo.

I tried to duplicate the steps you listed and could not replicate the problem. One thing I would suggest is that when you create the rectangle by center do not select the origin for the center, place it just off the origin then apply a coincident constraint after the rectangle is created to move the rectangle to the origin and see if that makes a difference in what you're experiencing.