Fully Constrained Geometry Becoming Underconstrained When Dimensioning Unrelated Line

[bponting4PSLZ]

Hi guys, I hope this is not something silly I'm doing. I'm attempting to draw a grid of construction lines over a projected shape. The horizontal lines went down alright, snapping to the projected geometry and are fully constrained. 

In another component (where the projected geometry comes from) there is a larger grid. The width of a cell is taken as a fraction of a pair of driven dimensions and stored in a user parameter, 'ModuleGridX' and 'ModuleGridY'.

Ideally, I would be able to specify 'ModuleGridX' as the spacing for the rectangular pattern on the smaller, problematic grid, but for reasons I don't understand, F360 won't allow me to use that parameter... it is just highlighted in red.

Now, because I can't use this parameter, I've instead added a driven dimension within this sketch which comes from the same dimension externally (the 939.3mm horizontal width in screencast). The rectangular pattern then allows me to select that driven dimension as the source for the spacing between the vertical lines.

When I repeat this same tactic on the horizontal lines, the existing, apparently fully constrained geometry of the vertical lines all move to the left, and all of the pattern repetitions show as underconstrained. Attempting to drag any of these points or lines around does not budge them, and I get this same result even before I dimension the line if I just draw the line first, then drag one of the points. The moment the point moves, all the vertical lines move again.

EDIT: Added project file. Can't add screencast for some reason... I get "Invalid HTML in the message body" error, even though I'm picking it from 'My Screencasts'??

EDIT 2: Link to screencast as suggested:

https://autode.sk/3cmwrHK

[jhackney1972]

You will need to attach your model so the Forum users can try and follow your workflow description.  In fact a Screencast to go along with it will help.  You mention something about a Screencast but it is not with your post.  If you do not know how to attach your Fusion 360 model follow these easy steps. Open the model in Fusion 360, select the File menu, then Export and save as a F3D or F3Z file to your hard drive. Then use the Attachments section, of a forum post, to attach it.

[bponting4PSLZ]

Thanks John for your reply. I have updated the post with project file but getting a weird error attempting to attach screencast from 'My Screencasts' about 'invalid HTML' in the post. Tried attaching it to this reply and have the same problem.

Hopefully the project file is clear enough. If you try to draw a horizontal line across the vertical gridlines, snapping to projected geometry, you should see the problem. If that doesn't break it, try dimensioning that line or dragging one of its endpoints.

Thanks for your help.

[g-andresen]

Hi,

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@bponting4PSLZ  schrieb:

…. but getting a weird error attempting to attach screencast from 'My Screencasts' about 'invalid HTML' in the post. Tried attaching it to this reply and have the same problem.

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This has been a known problem for a long time.
Copy the URL and paste it as a link in the post.

Günther

[bponting4PSLZ]

Thanks Günther, I've added a link to the original post.

[TrippyLighting · Accepted solution]

I am 99.9% convinced that the offset constraint in the sketch are responsible for this behavior. There are a number of threads with undesirable sketch behavior that all have this offset constraint in common.

If you can avoid dimensioning anything off an offset curve/line or re-using an offset sketch object for anything  else e.g. patterning, usually this does not happen.

Unfortunately, the sketch engine in Fusion 360 still has lots of room to grow.

Also, I would actually not pattern these objects in the sketch. I'd use component or body patterns.