Parameters and shifting (restricted) geometry

[letterle]

Hi there, 

Stuck on a project.

When i change the 'length' parameter, The geometry in Sketch 1 shifts around even though the geometry seems fully constrained.

also, 

Ive had to constrain every connection individually. When using the mirror command. The model grinds to a halt and fusion starts crashing.

In our work we often make models containing dozens or even hundreds of parts. being able to use the parametric feature is a gift but i keep running into bugs and limitations. Is there a more efficient way to model multiple copies of parts. Maybe something like instances in C4D.

Hope you can help. 

Tnx 

Roy

[Beyondforce]

Hi @letterle,

First thing first.

1. Start with a new component (R.U.L.E #1)

2. Sketch 1 - Create the Top and the Right frame, extrude them as separate bodies and mirror them.

3. Sketch 2 - Create one sketch on the Top/Right corner, extrude it and mirror it to the rest of the corners.

Now, it will solve your performance problems, because you have less sketches to calculate and changing the length won't shift Sketch 1 around!

IF, you still have problems after you change the Length, then use the Timeline to go back before the mirroring of Sketch 2, change the length and move back the Timeline.

If you still have issues, please let me know.

Cheers / Ben
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[letterle]

Hi Beyondforce.

As always I appreciate the feedback! The feedback on the forum has been awesome. In general good clean solutions. TNX for being a contributor!

this is only the first sketch of about 6 in total. We do a lot of parametric projects and up until now every project has grinded to a halt due to performance issues fairly quicky.

• #2 and #3  provide a workaround but unfortunately do not address the core problem of the shifting fixed geometry.
• Going back in the timeline to change parameters defeats the purpose of having a parameter. Also it does not prevent the geometry from shifting when i change the length to lets say 1200mm, Manually changing the dimension in the sketch does not prevent it as well

Posted a similar issue earlier. 

'Beyond logic'

TNX again 

Roy

[TrippyLighting]

Your design is a Top Down design and as I see it you have one skeleton sketch that you derive several bodies/components from.

It's a bit much to explain in detail in one post and I can create a screencast later, but the issues stem entirely from a sub-optimal structure of your design. In essence for the frame you should have one assembly, that contains 4 components, the 4 frame members. That assembly at it's top level will contain that single sketch, sketch5 in your design.

The components themselves only contain a body, which was created by an extrusion from the single sketch and then converted into a component.

In order to assemble these pieces in reference to each other you can then use a sign rigid group on that assembly. Make sure to have "Include child components" selected.

That assembly can then be moved freely as a whole and your frame will be able to parametrically update without it "falling" apart.

[letterle]

Hi TrippyLighting (Nice handle!!)

Thanks for the tip. This solves the components jumping around. My houskeeping was sloppy at best. Will try to better my ways.

The other part of the issue however is not solved. The second issue is the movement of restricted geometry in the sketch. When i change the length parameter in your sample the connections 3 of the 4 connections move. Again here I may have  been a bit sloppy but I've been fiddling with this for quite a while. 

Best 

Roy

[Beyondforce]

Hi @letterle,

I hope this will help.

I haven't extruded sketch 3, because I wasn't sure exactly how do you want it, but you can take it from here.

Cheers / Ben
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Did you find this reply helpful ? If so please use the Accept as Solution or Kudos button below.

Check out my YouTube channel: Fusion 360: Newbies+

[letterle]

Thanks for the help guys. 

But unfortunately this is starting to get very frustrating. I've been working for 3 days on figuring out how to get a simple sketch to behave properly. I'm not trying to draw a cathedral here. Its 4 lines copied few times and it has become a total nightmare to the point that its actually costing me the project.

Part of the original question was Why does sketch geometry shift around when you change parameters

I've seen the sketch break constraints

Had perpendicular constants that are clearly not  perpendicular anymore

Geometry flipping around especially fillets.

Why is it not possible to lock parts of sketches relative to each other (or make groups) in order to make an easy mirror? 

I would hate to go to Sketchup in order to save this project, 

Best, 

Roy

[TrippyLighting · Accepted solution]

I have designed a second frame in the same file also using a base sketch. the difference is that I move from a sketch to solid geometry as quickly as possible. 

Hopefully the screencast and attached file help in explaining what I am doing.

[letterle · Accepted solution]

He Guys, 

Thank you for the input. 

It's not pretty but most of the time its working. Occasionally, still got some geometry jumping around But, for now its good enough. 

Without you guys I would have given up un Fusion a long time ago.

TNX, TNX, TNX

Roy