Equal length constraint in sketcher in CATIA V5
Hi.
How can i go and put an equal constraint of two lines that must be the same length but the value is determined by other objects?
Example: doing a pentagon with a base circle that i input. Creating a 5side polygon inside the circle, and the actual length of the sides i can't input, it's determined by the circle, not the side. So I need a geometrical constraint of equal.
There are other ways to do.. I know, I know about eqivalent dimensions but i don't want to drive the value from this length. I've tried setting a parameter calculated from measuring the length of one side (refference constraint) and set eqivalent dimensions for the other lines with the formula of that parameter.. All good but when i change the input value (that is not the line, but the circle that defines the ends of lines) catia crashes all lines from the sketch dance around.
I know about Euclidian methods for a pentagon, or heptagon, and others, or that I can do it in shape design where a point sits on a circle, then circular patterned and then lines connect the points and the circle actually drives the points.
Also I can compute the chord value for any polygon and use that as the length and expect the circle circumscribed to be the exact value (but i don't trust catia's aproximation, it always end in .9999 or something. I know working on right scale, and setting max 8 decimals in options.. did that. Still don't like this method)
I just want to know if there is any geometrical constraint of "EQUAL LENGTH" as a geometrical constraint and not a value driving constraint.
In case of a polygon there are a multitude of variants, but i could find a lot of features that could use such type of constraint that are not patterned.
Accepted answer
Q: I just want to know if there is any geometrical constraint of "EQUAL LENGTH" as a geometrical constraint and not a value driving constraint
A: In CATIA V5, there is not a "Equal Length" constraint.
But, you can define a constraint's value as equal to the value of another constraint by using formulas. The easiest way to do this is:
1. constrain the length of one line
2. constrain the length of a second line
3. edit the value of the second constraint, type ' = ' for the value, Enter, and select the value of the first constraint.
2 Other answers
Hello Asi, before performing such task make sure you turn on the geometrical and dimensional constrains in sketcher (Image 1). Inside sketcher, draw a circle and dimension it via parameter (image 2). Then draw a straight line at the end of circle tangent to it. Now rotate the line about center for how many time you need (here instance is 4 and angle is 360/5) and trim of the excess lines (image 3). Now comes the play. You have to create the constrains like tangency so when the circle moves like will also move accordingly.
* Create a tangency between circle and line on all five sides (ignore for automatically created tangency constrains)(image 4)
Now make a desired operation (here extrude the pentagon with another parameter value) and while changing you get the result.(image 5)
Note I have made the circle as construction element
Thanks for your methods. As said, i'm enthusiast level in catia (i teach CATIA in an engineering university). Of course i know about geometrical and dimensional contraints in sketcher, as well as equivalent dimensions for multiple constraints, or give a parameter to be equal to another constraint as a formula. I'm not a pro since i don't CAD day to day real projects.. I just satisfy my curiosity and do research in my field of automotive engineering.
As for just the task of a polygon, the cleanest solution would be this one:
1. Create a point with a coordinate of Radius of the driving circle (with a parameter)
2. Rotate the point by the exact angle of the polygon (360deg/number of sides) set as a parameter with integer for sides number.
3. create a line between the two points
4 circular pattern complete crown with the number of sides as parameter for number of instances
5. join the whole thing.
There is the regulate polygon with the exact radius R, and however many sides i choose.
A bummer that such a nice constraint is not available in CATIA V5.
