DIMENSION VS. CONSTRAIN

[ideasuser]

Dimension or constrain which method is better. Is there any rule? I prefer dimension because there were no constrain for cad 10 years ago. But every time I put a dimension I ask myself "Should I do constrain instead? ". Is the file gets larger if I use dimension more than constrain?

 

[Shadowspawn]

There's a difference between geometric constraints (GC) and dimensional constraints (DC), and each has its place. When I do a sketch, I will apply the GS first according to my "design intent". Then I'll apply the DC to control the size. I think this makes the sketches simpler, and easier to understand and modify.

Additionally, I never use the 'fixed' GC, and very seldom use the 'point on curve' GC. These should be avoided like the plague IMHO. I also find it's also easier to understand the GC when you don't rely on the 'inferred' constraints. In-fact, the only inferred GC I use is the 'coincident' GC, and manually apply the others as I see fit...

YMMV

Regards,
SS
CAD should pay for itself, shouldn't it?

 

[jackley]

As Shadowspawn said it's based on the Design Intent.

But I use the point on curve constain from time to time when I have linked sketches from other part files in the assembly.

I would say apply the geometrical constraints first then the dimensional constraints. Try to think of downstream modifications, since this is where the money is made. What will be easiest to update.

Remember, simpler is always better.

Justin Ackley
Designer
jackley@gmail.com

 

[cbrn]

Hi,
I agree with the above posts. I personally use Point-on-Curve quite often though I recognize it can be "dangerous".

To make an example: if you know that two segments will always have the same length (because it's an intrinsic characteristic of the geometry you're modeling), then there is no point in dimensioning twice with the same dimension value: simply put "equal length" and you're done (and safer). On the other hand, if these two segments are "casually" of the same length because it's a possibility you're investigating, but you're not so sure this characteristic will be maintained in the future, then DON'T put "equal length" but rather dimension twice.

Regards

 

[Xwheelguy]

The Fix constraint does have its place, particularly when using Sketch Positioning dimensions in place of associativity between 2 different sketches (using the point on curve constraint).

If I copy/paste one of the 2 sketches that are constrained to each other into a new part file, then that associativity is lost without the 2nd sketch, which in this case I do not want or need. However, a sketch that is positioned using the sketch position dimensions can be reattached and repositioned without the other sketch.

I'm NOT arguing in favor of either method, just pointing out that there may be situations that call for geometry to be Fixed rather than constraining to an external reference such as another sketch.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

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