Distance Contraint

[Azum]

This is one of those non vital but extremly annoying things

Does anyone know what the criteria is in Inventor that determines if a distance constraint is a negative or positive amount. Logically it should be that it will be right 50% of the time but I find the error almost 100%. In other words whichever sign I put in it needs the other and so I always have to type in a correction to get the gap in the right direction
Someone suggested it moves depending on the mass of the object. I am sure there is a rule working here rather than pure bloody mindedness and I would really like to know what it is

 

[rollupswx]

I have never heard of a "distance constraint". Can you provide more information on what you are trying to do?

 

[Metalfixer]

It might be the "offset distance" in an assembly place constraint

 

[Azum]

Yes that is the one. If you choose zero distance the two faces are placed together. But if you choose a distance what determines which part moves in which direction. For example in the picture attached to get the leg fixed midway between the lugs of the foot bracket I need to choose a dimension which I know to be 14mm If I use 14 it will go one way and if I choose -14 it will go the other. 95% of the time I get it wrong. -14 one day will be right and the next day wrong. My question is what determines which bit moves in which direction?

 

[aardvarkdw]

If you use the "Mate" option, negative values will cause two faces to be separated and face away from each other and positive values will cause two faces to be separated and face toward each other.

If you use the "Flush" option, a positive value causes the separation to be in the direction that the faces are pointed and a negative value causes separation in the direction away from where the faces are pointed.

Unless the part containing face2 is constrained, the part containing face2 will move while face1 stays stationary.

Let me know if this is completely confusing and I will see if I can get some images.

David

 

[Azum]

Understand what you are saying but I do not think that is the problem. Consider the attached jpeg. I have picked the 2 faces that I want 14mm apart. The two faces are facing me so I pick the flush setting. If I pick the mate the leg will spin around and mate from the outside. The question is do I put in 14 or -14 to get the leg to sit between the side plates. To answer the question myself out of 6 goes 4 times 14 was required to get it right and twice -14 was needed. So what is the rule to know how to get it right every time without having to retype the figure when it goes wrong? I would really love to know. Cheers

 

[aardvarkdw]

Which part is grounded/constrained? If the leg is constrained you will want to use a positive value, if the bracket is constrained you want to use a negative value. If neither is constrained whichever part contains face1 (blue) will remain stationary (+ = blue in back and green in front ; - = green in back and blue in front).



David

 

[GABRIELCRAMER]

I find that paying attention to the little 3d arrows has helped me a lot and I only get it wrong once in a while. There is a pattern there but it's not very obvious. With the flush constraint I find that if you select the first face of the first part and then select the face of the second part a positive number will make the first part receade( not proud ) of the second. for the mate command, pay attention to the arrows. a positive number will increase the distance between the facing arrows and a neg does the opposite. I still can't get the angles quite right although I find it much more predictable to put the angle constraints on an edge instead of a surface. You will find that paying close attention to the position and direction of the vector arrows will help.

Ben