Coordinate system of an object/part

[mtran]

Hi,

I just moved to NX (previously an IDEAS user), and I'm having trouble with simple part/object movements. I created a surface wrt to absolute. However, when I try to move the part (Object Move command), the coordinate system associated with the part is at the center of the solid.

Is there a way to change the coordinate system of the part? I want to be able to move the part wrt to its CSYS using transforms, but need the CSYS to start at absolute (0,0,0). The only way I've found of doing it is by creating multiple Datum CSYS and moving from one CSYS to another.

This works okay, but then there is no way I can check that the surface wasn't accidently moved wrt to its own part CSYS.

I hope this makes sense, and thanks for any help.

 

[JohnRBaker]

Objects, except for things like Sketches created by referencing an existing Datum CSYS, Lines and Arcs created using points entered relative to a selected Datum CSYS or a parametic Point created using an Offset from the Datum Point (which is part of a Datum CSYS), are NOT created relative to the Datum CSYS that you see on the screen. Objects, parametric or otherwise, are created relative to the absolute zero of the Part file. Even if you move the WCS and enter values which are in relattionship to the WCS, internally the objects will still be defined using coordinates realative to absolutre zero of the Part file.

John R. Baker, P.E.
Product 'Evangelist'
Product Design Solutions
Siemens PLM Software Inc.
Industry Sector
Cypress, CA

http://www.siemens.com/plm

http://www.plmworld.org/museum/

To an Engineer, the glass is twice as big as it needs to be.

 

[mtran]

Hi John,

Thanks for the reply. However, I'm a bit confused now. The way you explain sounds like exactly what I want. Its not what I'm seeing though. Maybe I'm sketching incorrectly.

For example, if I created a simple cylinder where one the center is located at (1, 1, 1) wrt to absolute; when I try to move that object, the CSYS of the part is at the center of the cylinder rather than at absolute.

Thanks,
Minh

 

[JohnRBaker]

What version of NX are you using?

When you say that you create a "simple cylinder", are you sketching an arc and then extruding it? And is the arc actually part of a SKETCH and not just drawn as a circle?

John R. Baker, P.E.
Product 'Evangelist'
Product Design Solutions
Siemens PLM Software Inc.
Industry Sector
Cypress, CA

http://www.siemens.com/plm

http://www.plmworld.org/museum/

To an Engineer, the glass is twice as big as it needs to be.

 

[mtran]

I'm running NX 7.5. I sketched a circle and extruded. My model history shows this order:

1. Datum CSYS.
2. SKETCH (1)
3. Extrude (2)

 

[JohnRBaker]

OK, starting in NX 7.5 when you create a Sketch you have the option of linking the sketch to the existing Datum CSYS (which make it the parent) or having the sketcher create it's OWN local Datum CSYS (which will become the parent for the Sketch).

To change this setting (the OOTB default is to create a new local Datum CSYS, although this can be turned OFF in customer defaults), when the Create Sketch dialog comes up, go to the Settings section and toggle OFF the 'Create Intermediate Datum CSYS' option, and then continue by selecting the desired Datum CSYS as the Sketch parent. Note that once you've made this selection, dialog memory will retain this setting until you change it back.

However, may I suggest that if you this alternative workflow, that you may also wish to go to...

Preferences -> Modeling -> General

...and toggle OFF the 'Automatically Make Datums Internal to Child Sketches'. Trust me, if you don't you're going to be scratching your head over this as well (this can also be changed in Customer Defaults).

John R. Baker, P.E.
Product 'Evangelist'
Product Design Solutions
Siemens PLM Software Inc.
Industry Sector
Cypress, CA

http://www.siemens.com/plm

http://www.plmworld.org/museum/

To an Engineer, the glass is twice as big as it needs to be.

 

[tsjaikdus]

> the CSYS of the part is at the center of the cylinder
> rather than at absolute

???

You use dimensions to attach the center of the circle to the datum axes, the datum planes or the datum point. Whichever you prefer. Now the circle is defined at (1,1). Then exit the sketch and extrude with start at 1. Now the cilinder is at (1,1,1). That's it.

If you want to move the part, use a parent for that i.e an assembly part.

 

[cowski]

It sounds like you are referring to the 'dynamic csys' that appears when you start the 'move object' command (with dynamic move option). If that is the case, you can select the 'move handles only' option to move it to a more convenient orientation before performing the actual move operation. Also, I believe if you right click while in the 'move handles only' option you will have the opportunity to align the dynamic csys to the wcsys.