Dimension is constraining itself

[Anonymous]

Hello.

I have a 3 month old project that I'm trying to edit now without any success.

The problem is that I'm trying to change a dimension, but such dimension is constrained by dimension D1, which happens to be itself. If I delete it and try to add it again it says that I'll be creating an over-constrained dimension. What is the problem? Who can I find what is actually constraining the line I want to modify?

If anyone wants to take a look here it is:

https://a360.co/2XgJkaE

[TheCADWhisperer]

I think that  your first sketch is far far more complicated than it need be.

Pattern features rather than sketch elements and keep sketches relatively simple.

I see a ton of unnecessarily repeated geometry/constraints/dimensions in your first sketch.

If you find yourself repeating items - you are probably doing something wrong.

Strive to fully define each and every sketch before continuing on to next step.

Make use of symmetry about the Origin.

[Anonymous]

Thanks for your answer.

Most of the repeated structures were actually built using patterns, but I had to break the pattern later because I was not able to make them fit properly, so they ended being different sketches.

Leaving my lack of experience apart (still learning so I'm going to do it better next time for sure), is there anything that is keeping me from being able to change the width of the main sketch? I am unable to reduce it a couple of MM and that is being a real problem for me.

[TheCADWhisperer]

If this were my design - I would start over from scratch.

[TheCADWhisperer]

OK, 

I have taken a closer look.

I would delete everything in Nest sketch except for the outer boundary and  the "cloud" type spline profile.

My next sketch would have the 4 corner circles and the rectangle for the HigroSLot (in the Nest).

The third sketch would have one example (and only one) of each unique ellipse.

Then forth sketch would have one example (and only one) of the rectangular feature to the right side of the Nest....

...and so on.  Keep sketches simple, no duplicated sketch dimensions (or very very few) and no duplicated sketch elements. 

It is better to pattern features than sketch elements.

I would not have any user created workplanes (not that I never create workplanes, but they just aren't needed in this design).  (Maybe Plane3, but it isn't really needed - using the BORN Technique, I try to avoid unnecessary dependencies.)

I estimate total time to remodel at about 3 hrs.

Edit: 

Sketches -

Nest, Deposit and WhaaterHole are far more complicated than necessary.

Edit 2:

Normally I would start over entirely from scratch using what I learned from initial attempt to create clean geometry.

Because of the complexity of the "cloud" feature spline - I would first make a copy and try the above steps rather than entirely from scratch.

Edit 3: 

This could be easier than I initially thought.

The geometry is in better shape than I expected.

I tested Project necessary sketch geometry into new sketch and then Break Link before deleting unnecessary geometry from the complicated sketches and it worked fine.

I wish I had time to make a video on the process.

I think you would be surprised how much better the end result would be.

[TheCADWhisperer]

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@Anonymous wrote:

1. Most of the repeated structures were actually built using patterns...

2. ...is there anything that is keeping me from being able to change the width of the main sketch?

1. Built using Sketch patttern, not feature pattern.

2. Tip: What is the significance of green sketch geometry?

[TheCADWhisperer · Accepted solution]

@Anonymous 

Did you figure it out?

[Anonymous]

Hello @TheCADWhisperer 

Wow, again you manage to amaze me with the support given. At a first read, I'm not able to understand all what you just said to me, so I will make a couple of extra reads to see if I can get most of them.

Glad to hear that, at least, I didn't screw it that bad with my limited knowledge (you literally said it was not as bad as you thought so, I take that as a good sign 🤣)

You asked me about the green stuff, those are locked geometries. I did that for avoid moving them mistakenly, and they are in fact the root of my problem.

Sorry for not answering before, I just been a bit offline.

Thank you very much!

[Anonymous]

Ok, I re-read all your answeres for a thid time and I think I got everything you said, however, this opens up new questions for me.

One of your most repeated advises is about using pattern features instead of pattern sketches. Pattern sketches have been a real pain, so I think this makes sense. However, this creates some uncertain feeling to me.

You may noticed that, in order to create different levels of depth, having some tunnels in the background and some on the foreground, I had to extrude sketches differently. In order to be able to do this with features I will need at least two sketches for the two possible depths, then pattern each one? Or will you extrude the same sketch twice and just omit certain parts on the feature pattern?

You have also mentioned that I should separate my main sketch into several ones. I literally tried to avoid this at all cost, so I'm curious about what is considered best practice here and the motivation to keep them separated.

That said, this also introduces another question into my head: how can I constraint different sketches between them? Most of my sketches are relative to the outline, so having them separated will require an extra feature that I'm not sure I know how to use, which I think it is projections. Am I correct?

Thanks again.

[JDMather]

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@Anonymous wrote:

1. ...for the two possible depths, .... just omit certain parts on the feature pattern?

2. I literally tried to avoid this at all cost, so I'm curious about what is considered best practice here and the motivation to keep them separated.

3. That said, this also introduces another question into my head: how can I constraint different sketches between them? ...I'm not sure I know how to use, which I think it is projections. 

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1. When you Pattern a feature you can check/uncheck what instances you want in the pattern.  You can use Press/Pull after creation for different depths.

2. Geometric constraints such as Horizontal, Vertical, Parallel, Perpendicular... ...become very computationally expensive to solve as the number of constraints increase.

For a rectangle you might have 4 geometry constraints (not counting coincident endpoints) and two location dimensions and two size dimensions.  That is solved for one rectangle.  If you pattern the feature, the previous has already been solved.  If you pattern the sketch geometry - you have now significantly increased the complexity of solving those additional constraints.

In my class I use a gear or sprocket to illustrate the issue.

Best to do one solid tooth and pattern the tooth rather than pattern sketch elements.

3. Project the key endpoints or lines from one sketch into next sketch.  If you want really robust sketches - use ONLY the Origin Center point as your single datum reference for all sketches.  This might not always be practical, but is the most robust technique.  With default settings Fusion will autoproject geometry in an attempt to help you.  In my experience this causes more issues than it helps, so I prefer to turn off and explicitly indicate what geometry I want projected.

I am putting this particular example of your ant farm into my "book" folder to use as a demonstration sometime in the future of how to improve technique.  (I have been working on this "book" for many years, so don't hold your breath waiting for it to be released.)

[Anonymous]

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@JDMather wrote:1. When you Pattern a feature you can check/uncheck what instances you want in the pattern.  You can use Press/Pull after creation for different depths.

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Yes and no. I can do that, make different press and pulls, ben then they become one single feature. In fact the tunnel connecting different chambers and the chambers themselves become one single feature despite I created them separately.

Thanks for your explanation about the computational cost, it makes sense. My computer is struggling from time to time when I edit sketches and I was wondering why.

About the project thing, I was expecting that to be the solution, but as you said, it created more problems than solutions to me so far. Using the origin as absolute reference makes sense and feels like a interesting solution. Probably using formulas and variables for sizes may make this easier.

[Anonymous]

I thought I found a way to independently pattern each section of a tunnel and a chamber, but then I get this error: