Newbie question: Relations

Hi All,

Can someone please point me at a description of SW "Relations". I am
very new to this great tool, but I can't find a description of what
exactly a relation does.

I initially thought that it was used to associate to entities. I
generated a pair of verticals, then created a vertical relation.
Changing one of the vertical lengths didn't alter the other some so I
am quite confused.

Many thanks,

Mark.

 

You are on track, but not interpreting quite the way "Vertical" really
works.

Vertical merely means that in the sketch, but nothing else.

If you want two lines to be parallel, then select the two & click
"Parallel" or "Perpendicular" if that is what you want.

If you have two lines that are "Parallel" and you want them to remain
that way, you can put a construction line between each of the ends
"Perpendicular" and the dimension on one line will drive the other line
length to be the same as the first line.

Bo

 

Hi Bo,

Many thanks.

Is there anywhere that this is all written down.

It seems like it should be a topic for a tutorial or a background
document.

-Mark.

 

I think the "old" paper tutorial had some discussion & examples, and I
am sure the existing "Help" files will get you in fine shape.

Search Help for "Sketch" & then go down the list and double click on
"Sketch Relations".

Later - Bo

 

Hi Bo,

Many thanks, that is exactly what I was looking for.

-Mark

 

I don't think your explanation was quite correct for the person that is just
learning.

The statement here is that you want them to remain parallel - they will do
that until the parallel relation is removed - nothing else is required.

If you want them to stay the same length, then add an equal relation - the
lengths will then stay matched.

If you want the ends to stay horizontal to each other, add that relation.
If the lines are not vertical or horizontal, but you still want other
relations, add what's need in that case.

The whole point here is to add what you need as relations, when possible,
rather than creating extra geometry that doesn't actually produce a surface
or solid. I know that sometimes that's not possible, but a yet a good
practice to learn right from the start.

WT

 

Do they still teach Geometry in high school?
I remember taking geometry first semester of high school back in '71.
We learned what parallel, perpendicular, horizontal, vertical and
tangent meant. I think we learned what equal means some years earlier.
Don't make it harder than it is.
As you start experimenting click and drag lines arcs or endpoints and
by observation and logic you should be able to figure out what
relations are needed to constrain your sketches.
Also experiment with using construction lines to help constrain your
sketches. And the construction lines help someone else quickly figure
out your geometry when it comes time to edit. I haven't used
construction lines this much since leaving the drawing board nearly 20
years ago!

 

Hi Wayne,

Many thanks, you provide lucid insight with few words.

I am struggling through the examples and still can't get my head around
a "Coincident Relation". I need to attach the mid-point of a folded
piece of sheet metal to the mid-point of a sketch above it for allow me
to add a tab. It appears that the mechanism to connect these mid points
is the use of a Coincident Relation. This will ensure that the Tab is
centred on the folded piece.

The folded piece is Black, so I think that means that it is resolved,
and therefore fixed. The sketch is blue, so I assume that it will move
towards, and attach to the folded piece when I have completed the
operation correctly.

Are my observations and assumptions correct ? I have spent quite a
while right clicking mid points of lines, only to see them vanish when
I right click the surface that I want to attach to. I have seen A
Coincident pop up in "add relation" once, but trying to accept it told
me that illegal geometry would result.

Any indicators to what I am doing wrong will be appreciated.

Thanks,

Mark.

 

Black and blue have meaning in the sketch only. The part has whatever color
it has and won't move if it is fixed or mated properly.

Unfortuantely, midpoint selections are pretty flakey. They work sometimes
and sometimes they don't. For me, it's usually the latter, so I tend not to
use them. I do things like put a point on the line and then give it the
midpoint relation, or put a line perpendicular to the line and add a
midpoint relation to the end point of the added line.

This was probably something else happening. The move that the relation was
forcing might have been shortening a line down to 0 length, for example.


Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"