topic Sketch dimension ambiguity in Inventor Forum

Sketch dimension ambiguity

gerrardhickson — Mon, 22 May 2023 00:37:09 GMT

Hi all,

I've been using Inventor since R14, and there has always been a problem that shows its head from time to time when dimensioning sketch points (possibly other occassions too). The problem is dimensional ambiguity - that is, when a set of given dimensions and constraints result in two (or more) possible and valid solutions.

Here's an example, that almost bit me this morning.

Here is the sketch as intended - note d190 is 50mm from the edge of the flange.

Here is the sketch as I found it after opening the file this morning:

note d190 is still 50mm from the edge of the flange, but its flipped to the opposite side.

In my case, this resulted in a clash that could have resulted in hundreds of these panels being issued wrong. Fortunately for me the drawings had already been issued to production, and were correct at the time.

My question is - have other people overcome this problem reliably? If so, what techniques are you using to remove the ambiguity?

Thanks

Re: Sketch dimension ambiguity

swalton — Mon, 22 May 2023 02:32:13 GMT

I haven't seen the behavior that you are. Did the number of flanges on the part change between the good sketch and the unexpected sketch?

Its hard to tell from your screenshot, but is d190 tied to the endpoint of the bend line or to the projected edge of the flange? I'm not sure if it will make a difference.

Re: Sketch dimension ambiguity

gerrardhickson — Tue, 30 May 2023 03:38:23 GMT

@swalton - You were right, it was attached to the point, however, I came back to this part today and found the same problem had occurred again.

I can confirm that (this time) the dimension was applied to the line, not the point.

I dug a little deeper via VBA, and I can demonstrate that the dimension was attached to a line and point and that the dimension had incorrectly set the DimensionCenterPoint. Notice the Y Value from the DimensionCenterPoint object below.

Before:

After:

Re: Sketch dimension ambiguity

JoyceZhou — Tue, 30 May 2023 06:01:11 GMT

@gerrardhickson Could you share the part so we could check on my side? thanks

Re: Sketch dimension ambiguity

gerrardhickson — Tue, 30 May 2023 09:59:45 GMT

Hi Joyce, I'll send a PM with the download link to the file.

I should also mention that the part has model states.