Very Simply Sketch Question

[DavidCambridge]

Hello All

I’m very new to Fusion 360 (which I think is brilliant, and amazing it's free for hobby use!) and I’m having a real hard time getting my head around how sketching works.

In the simple example below I’ve created a rectangle offset from the origin. I’ve added one dimension.

If I change the dimension, I can see that the rectangle is shrunk to fit the new dimension.

I understand that if I add more dimensions to the rectangle this won't happen - but I'm finding with a complicated sketch that this gets quite fiddly.  What I actually want to happen is the rectangle to move up without it changing size. Is there a way of doing this without having to completely nail ever dimension and constraint of the rectangle ?

I'd really appreciate some help as I've been battling this for a couple of weeks now, and getting my head into the fusion 360 sketch mind set is proving much harder than I thought!

David

[Anonymous]

Interesting, When I try it the rectangle moves without resizing.  Just one rectangle with a sketch dimensions from the bottom edge to the origin? Nothing else? Now I'm curious

[DavidCambridge]

Here is a link to a screen capture on you tube that shows exactly what I was doing

[jeff_strater]

You are both right.  In @DavidCambridge's example, he creates a line from the origin to the bottom line of the rectangle and dimensions that line.  What I suspect that @Anonymous did was just dimension directly from the origin to the bottom rectangle line, as in this screencast:

How Fusion's sketcher (and any CAD sketcher that I know of) works is to solve a set of geometries, dimensions and constraints together.  For a system that has too-few constraints and dimensions, there are many valid solutions.  Depending on a wide range of factors (initial conditions, order that the constraints are applied, etc), you will get different results.  For your example, because it is under-constrained, what you see (the changing of size of the rectangle) is a valid solution to the set of input geometries and constraints.

Bottom line:  If you want your  sketch to behave predictably when you change it, you will need more dimensions and constraints.  Even if we could make this case behave as you'd like, the results once you add more to your sketch will always be unpredictable.  So, yes, you need to add more dimensions to get predictable behavior.

Jeff Strater (Fusion development)

[DavidCambridge]

Thanks Jeff. I really appreciate the help. What you say makes sense and as you say it doesn’t matter what Fusion 360 does somebody will want it to do something different.

My rectangle box was a very simple example, in reality I was trying to do something more complicated and I was having a hard time getting all the constraints correct. What would be really nice is if I could create a group of sketch elements that all behaved and moved as one. It may be that this is a feature request, but it maybe that it’s already possible and I just haven’t discovered how yet?

Either way, I hadn’t realised that I could have a dimension on its own. But now you have taken the trouble to demonstrate it in the screen cast my immediate problem is solved so thank you very much indeed!

David

[TrippyLighting]

This sounds like you want to be able to group certain sketch elements together without having to add dimension and contraints between all the elements.

Then you want to be able to move the group. I that a correct assessment ?

If so, yes,  that has been requested at least one. It is very useful, for example if you import text from a vector graphics application and want to be able to move the individual lettes. Right now this is very tedious.

[DavidCambridge]

Yes - that's exactly it!

David

[jeff_strater]

I think you are asking for something like "sketch blocks" or "sketch rigid group".  Somewhat surprisingly, I could not find this suggestion on the Fusion 360 Ideastation.  Feel free to create a new idea there, and see if others share this requirement.

Jeff

[DavidCambridge]

Thanks Jeff - I will do so.  

In the mean time I now have a new question that is still related to sketch dimensions.  In this example I add a new line to my sketch, which as far as I can see is independant of other lines and dimensions. However, when I change  the new line dimension it seems to have a profound effect on the line to the left that I can't see is related to it. As before I'd be really grateful for some guidance as to why this is ?

Thanks

David

[jiang_peng]

Hi David,

It looks a bug. Thanks for reporting this! Could you please share the link or attach the f3d file here? We will look into it.

thanks

[DavidCambridge]

Thanks for the help with this. Unfortunateley I no longer have the drawing that caused the problem. When I deleted , and then re-created the same sketch the problem went away.

David