Origin of new parts in an assembly

Hi. I'm fairly new to SolidWorks and have a question.

What controls the orientation of the origin when starting a new part in an
assembly? For example, say I have a part that's a cube in an assembly file.
I want to start a new part on the top of the cube. I click on the top
surface to position the initial sketch plane for the new part and the origin
is placed at the back left corner with the x axis pointing to the left--180
degrees from what I'd expect.

Does the user have any control over the rotation of the origin, before or
after placement of a new part?

Thanks...

Brian

 

I know of the sketch modify tool, but it seems that it only works after
sketch geometry has been created--in other words, I can't rotate the sketch
origin BEFORE creating any geometry.

What's the tool to alight a sketch to a model edge?

Also, if there's a diagram as you mention below, I'd love to see that... if
anybody has it, can you post it? Thanks for the help!

Brian

 

I wonder if perhaps you're getting hung up on something that's not
really important. One thing to realize -- when you insert a new Part in
an Assembly you create an InPlace mate. That mate isn't NECESSARILY
what you want to keep . . . unless you REALLY want to link features to
other Parts in the Assembly, and even then the InPlace mate isn't
necessary. Personally I recommend creating as much of your Part as you
like, then exiting the Part, deleting the InPlace mate and creating
geometric relationships to locate your part in the Assembly. Doing it
like they teach you in class -- creating a tapped hole to line up with a
clearance hole -- can be valuable, but such in-context relationships are
a double-edged sword and you have to watch them, ESPECIALLY if the Part
you create is going to be used in more than one place. As mentioned,
you don't need an InPlace mate to keep such a relationship anyway, and
you don't need to have your X, Y and Z axes coincide between parts in an
Assembly. That doesn't really buy you anything valuable. Worrying
about it is counterproductive. Just insert your new Part on whatever
Plane or face is useful, create your sketches and features and carry
on. It's MUCH more important to learn about what is going on in
SolidWorks as you make your sketches fully defined (and you certainly
should make them fully defined -- and idependent except where you really
need to maintain in-context relationships) than it is to keep axes the
same from part to part. Having come out of training class with a pretty
good idea of how to get what you want from SolidWorks by hook or by
crook you may think that you have a good handle on how to make sure
sketches are properly defined . . . but I can almost assure you that you
don't. Spend time on THAT, not on your current concern.

Mark 'Sporky' Stapleton
Watermark Design, LLC
www.h2omarkdesign.com

 

Mark,

I agree with everything you've said. I come from an MDT background where
the UCS (origin) means something. It's really just about understanding why
it works the way it does. If, for example I learned that picking near the
lower left corner of a face caused the origin to be placed in that corner
and aligned 'normal', I might be inclined to pick there when creating new
parts. That's all.

I also don't like the in-context relationships that you mentioned; I like
the ability to build off of other parts in an assembly, but I do NOT want
them linked in any way. That's another question... can that be turned of or
disabled as you work in an assembly? In Inventor, if you hold down the CTRL
key as you pick geometry, it'll inference lines, arcs, points, etc. but they
are not linked in any way. I don't know if I explained that well; I'll be
asking more about this in the near future.

Thanks for the response. Although I agree with you, I'd still like to know
why how the origin finds its home and orients itself. Hopefully somebody
has the answer. Thanks!

Brian

 

Yessir, I am. I preach its importance to my coworkers. So, it's odd that
it has little meaning in SW--something I'll have to get used to. Thanks for
your help--there will be more questions coming...

Brian

 

I did. We didn't use 3D AutoCAD for very long though... only for a couple
of months until we got MDT (1998 I think).

 

Basically, Brian, I think you'll find that if you insert a new Part on
an Assembly plane, that plane (whatever it is) becomes the Front plane
of the new Part, but with the origin located coincident to the Assembly
origin (different plane definitions, perhaps). If you insert the new
part on a plane of a Part in the Assembly basically the same kind of
thing occurs, except the origin becomes coincident with that Part
origin. If you insert the new Part on a face of a component, the Front
plane of the new Part becomes that face, and the origin becomes
coincident with the referenced Part origin.

I'm not certain I answered your question, but I hope it helps.

'Sporky'

 

SW2005 can turn that off so you can inference, but not reference.

WT

 

Is that an "as you sketch" option that you can selectively use, or a system
setting that is always on or off? Either way, I like that it's available...

Brian