Sketch not showing fully constrained

[BWENGUK]

Slightly confused here. Produced this quick sketch, which I believe to be fully defined, yet the two smaller circles on the right are showing as not constrained. If I draw a sketch line going to the lines, it then shows as constrained, yet I can't see what constraint adding that line is creating.

The circles can't be dragged anywhere. And no more dims can be added without them just becoming ref dims. Is it possible with the given dims that there is another place those circles could be and the dims still be the same?

[TheCADWhisperer]

@BWENGUK 

Can you reproduce this behavior in a new file from scratch?

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

OK, I reproduced the behavior myself from scratch.

[BWENGUK]

The actual dims are not really important.

Just a bit of a weird quirk, using those dims to produce a constrained drawing.

[g-andresen]

Hi,

I think it's a bug.
Because if you remove the two construction lines, the sketch remains fully defined.

günther

[javelin_exile]

Auto constraint showed up today so I've been paying with it.  I have a few sketches made from projected geometry that it fails on. but they were pretty complex and took a long time to process, the simple ones have been better and more complex sketches if built gradually and run auto constraint at intervals and it seems to get everything to turn black.

Edit: I'll make a new thread as this might be helpful to someone. If I export the sketch to dxf and re import it. I get  a fully constrained result as a second choice and the first choice seems the same with some blue details remaining.

[BWENGUK]

@g-andreseninterestingly for me if i add the sketch lines to make it lock to fully constrained, and then delete them, it becomes unconstrained again.

[g-andresen]

Hi,

that´s what I see

günther

[BWENGUK]

@g-andresenwhere you have the 77 dim, instead of constraining the left hole using the horizontal constraint, instead sketch a line between the two and contain that line horizontally instead. For some reason, that means that deleting the lines makes the drawing unconstrained again.

Also, if you 'fix' the central circle, that seems to fully constrain the sketch too, even if it's already fixed to a specific point. This is just a big odd!

[BWENGUK]

 In fact, playing around with it a bit more, it's even weirder. If you delete the horizontal constraint then add it back in the whole sketch, the snaps to fully constrained, even though nothing has technically changed. Think there's a gremlin in there somewhere.

[g-andresen]

Hi,

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@BWENGUK  schrieb:

 Think there's a gremlin in there somewhere.

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If I catch it, I'll let you know

günther

[Phil.E]

Mine is fully constrained

[TheCADWhisperer]

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@Phil.E wrote:

Mine is fully constrained

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@Phil.E 

Is this a Vertical dimension or is it an Aligned dimension?

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

[BWENGUK]

@Phil.Eit makes a difference whether it's a direct dim or a vertical dim.

[BWENGUK]

I wonder if it's because these two drawings technically share the exact same dims, even though they are obviously different.

[g-andresen]

Hi,

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@Phil.E  schrieb:

Mine is fully constrained

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However, this does not change the fact that the identification method is not comprehensible.

günther

[Phil.E]

You are correct. It was my failing to not see that the right hand dimension was aligned. Probably because as a designer I would never layout a hole pattern like this, it's a bit incomprehensible what this might be useful for. So my brain penciled in the most logical solution which was to use linear, rather than aligned dimensions. 

Aligned dimensions are, in my design experience, nothing more than radial dimensions. I use construction lines, arcs and circles when I need to locate a hole at a fixed distance, at an angle. I think in terms of distance/angle, not pure trigonometry as this example uses. 

Don't get me wrong, it's a failure of my imagination. Here's what my brain sees when I see a hole pattern like this.

Thanks for the good example of a false under constrained sketch diagram!

[g-andresen]

Hi,

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@Phil.E  schrieb:

 So my brain penciled in the most logical solution which was to use linear, rather than aligned dimensions. 

I share this view based on my experience as a mechanic.

günther

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[BWENGUK]

@Phil.Eand @g-andresen this is something that crops up a fair bit I seem to find.

I often use aligned dimensions like this when creating a part based off of a sample given to me. In this case, this was the part:

You can probably see from this how the easiest way to constrain the hole locations for me was to just do distance between holes. Easy to accurately measure with hand tools.

Yes, if I was designing this from scratch, that's not at all the best way of doing it, but I'm often using sketches like this to turn real parts with weird sizes into something I can work with digitally.

It's not a massive bug, but thought it would make for an interesting thread!

[Phil.E]

Thanks for the example. My first inclination would still be to use construction lines to set distance and vector from each other. The sketch logic that checks fully constrained status is going to see a dimension and a construction line differently. The sketch dimension object has logic to prevent flipping, and is tied up in the parametric table logic, while a construction line has only magnitude, vector, and end points. They work well together, doing separate jobs.

But yes, we can try to fix every single corner case, and we do when we get them. I'm just explaining that construction lines have simple logic compared to dimensions and it works better in the system. Thanks for sending it!