Is finding constrains based on guessing (or is there a way) ?
Hi,
I would strongly recommend that you do the embedded tutorials in the Fusion Documentation and also some of the
Self-Paced Learning to help you to learn fusion faster and better. They can be found here:
It is also much easier for the forum to help you if you attach your file AND a screenshot of what you want to achieve
and what the problem is. You can create a file to export like this:
Time spent on the tutorials and self paced learning will not be wasted. Also check out the three RULES that are
pinned to the forum for further guidance.
In this case, you are in desperate need to read the documentation about constraints. Constraining a sketch is
all about making sure that everything is properly defined. A line is not just a line with a length. It starts
somewhere and finishes somewhere in relation to some Origin. The line may be straight - is it parallel to one
of the axes? Is it parallel to another line? Is one or both ends co-incident with another line or point? All of
these questions need to be answered for a sketch to be fully defined.
Fusion now makes it VERY easy to auto-constrain a sketch, but you should know how to properly constrain a
sketch without this tool, because fusion makes pretty good guesses, but they are not always constraints in
the way you may want or need.
The easiest way to see if a sketch is fully constrained is to look for the Lock icon on the sketch.
Lock icon? - fully constrained
Little pencil? NOT fully constrained.
Next, look for lines that are blue. If it is blue then you can move it somehow with the mouse. Either one or
both ends or even move the whole line. Have you defined a length? Is it meant to be horizontal or vertical
to the origin? Is either end meant to be co-incident to another line or point?
Points should be solid black - if they are open black circles then they are not constrained.
The constraints list should help give you a clue.
Is a line tangent to a curve? How many degrees is that arc? Are those two circles Concentric?
These are all questions you should be asking yourself. This is not magic. If you draw a line
freehand on paper you are less accurate, but you assume that a line that looks to be parallel
to the edge of the page to BE parallel to the edge of the page. There is only so much that
fusion can guess. YOU need to fill in the gaps.
Take a line you have drawn freehand. You know in your mind that that line has a 1 degree slope
for some reason. How does fusion know that? If you use the Auto-Constrain function that has
been released this month, I would guess that fusion would put a horizontal constraint onto your
line - bing, you sketch is fully constrained, but it has an error. YOU know that the line should have
a 1 degree slope. You need to TELL fusion this.
The reason you are struggling with identifying constraints with your sketches is because you don't
know how they work and it is vital that you do. Some lines can have several constraints on them, all
valid and all needed. The best thing you can do is read the documentation for each type of constraint
until you have your head around them. This time will NOT be wasted.
After you have done this, practice a lot. If you are still struggling then post again and we will help.
Cheers
Andrew
1. Keep sketches simple.
2. Use real world examples of a sketch. You are working in a 3D CAD software. What 3D geometry would you create based on that sketch?
3. Avoid double lines. For example the two diagonal lines are two lines overlapping each other 100%
Figuring out what constraint belongs to what sketch element isn't always straight forward and sometimes it's easier just to delete a sketch object and re-draw it.
My last a probably most important piece of advice is this:
You are working in a 3D modeling environment. Use as little sketching as you can get away with. Do everything else with 3D modeling features.
Avoid mirroring in sketches.
Avoid patterns in sketches.
Avoid fillets and chamfers in sketches.
There are exceptions, of course, but most of the time that works fine. 90% of the sketch related problems on this forum could be avoided if user would adhere to these simple guidelines.
