Constraint Bugbear

[garytinker]

hi guys,

can anyone tell me if there is a way to get around this issue im having because its driving me nuts,

ok so it should be simple. I’ve got a spacing of 120 with a 8mm gap between them, (these are constant)

there are 2 triangles in the bottom and top, all i want to do is make an equals constraint that states that 29.3 and 27.2 are in actual act the same number, I don’t even care what that number is,

Yes I know I can:

* draw line perpendicular to the inclined line from one corner

*draw a parallel line from the adjacent corner,

*sketch a reference line find the centre point,

*draw a perpendicular line and then

*set up a symmetrical constraint

Blah Blah Blah,

Or i could go into relations

*make some trig calcs

*set up a relation that equals half of the hypotenuse and

*define a centre line

*and offset the bars from there.

But that all takes way longer than something that should be so simple, and as we all know time is money.

so anyone got an idea?

[garytinker]

ok i tried something elce as well and it faild at math horribly

i went in to relations and said

d1 = (d1+rd2)/2

where d1 = the 29mm dim

and rd2 = the ref dim

relations ok'd it, and when i regened it the numberes cycled through some variables( which i have never seen before) and in the end it stoped with 2 un equil numbers, probbily got stuck in an infinite loop and stoped it

so ill probbibly ad a ref dim that is

total lg

and then go

d1 = (t_length-((e1*4)+(e2*3)))/2, still this is taking way too long for something so simple

[garytinker]

yup that worked........ still anyone with a better system please tell me

[TomD.inPDX]

I tend to use a lot of constructions circles with equal diameter and tangent constraints. In your case, I can see 3 different size circles each dimensioned to manage the desired result.

[TomD.inPDX]

...what are those E1 and E2 dims?

Here you go...

[garytinker]

the e1 dims are a result of me telling Creo that dim2 &dim3 = d1 using the = button in the constrain tab.

so if I change dim1 dim 2 and 3 automatically update

ill give the circles a go its probably faster than making a relation, still it should be easier than that

i dont know, i tend to use the relations a lot, including assembly level relations changing part level dims

[TomD.inPDX]

I'll be damned! Never knew you could do that to dimensions

[garytinker]

yea its a handy one, saves a lot of time when doing size re-gens

[JonathanHodgson]

It looks like your dimensions 29.3 and 27.2 are actually each dimensioning the length of a line entity... can't you just set an equal length constraint on those two lines?

Or am I missing something else?

[TomU]

Your sketch is over constrained. By constraining the outer construction lines to the corners of the rectangle, you can't control both the 8, the 120, and the 29.3. Something has to give.

1.) Temporarily delete the corner constraint.

2.) Dimension the distance between each outer set of construction lines.

3.) Set these two dimensions equal to each other.

4.) Delete the remaining outer dimension. The two outer sets should still be equal to each other, but no dimension.

5.) Re-constrain the corner back to the line.

[TomD.inPDX]

This is where you would use the equal diameter construction circles. Center the vertex of the rectangle and tangent to the outside line. This way, you didn't dimension it, but whatever the radius, they are equal.

Otherwise yes, it would be over constrained because the equal dimensions are after all, still dimensions.

Can you make reference dimensions equal?

[TomU]

The equal diameters are really no different than equal dimensions. The issue in this case is that he can't create the two dimensions (in order to later set them both equal) because doing so will overconstrain the sketch. By temporarily freeing up some other part of the sketch (like the corner constraint), the dimensions can be created and set equal, then the extra dimension deleted and the corner reconstrained. And no, you can't set reference dimensions equal to each other.

[TomD.inPDX]

Not exactly. The difference is that the construction circles are -not- dimensioned, therefore their diameters "float" equally. You can do the same with construction lines but circles are easier to manage.