Parametric design works, almost

[GregHeumann]

So, as an exercise - and to help me think about how I'm going to machine this solenoid engine crankshaft, I drew this up with the intent of it being fully parameterized.  And everything responds the way I expect to parameter changes EXCEPT the large diameter (parameter: WebDiameter).

When I drew this, also sort of as an experiment, instead of creating a bunch of planes to draw the web circles and extrude them, I extruded boxes up from Sketch 1, dimensioned with WebDiameter. Then I used them to define the sketch plane, drew the circle, and constrained it to be tangent with the sides of the box. Then extruded the webs using "intersect" - voila, box disappears, extruded webs are created. 

But if I change this parameter up or down from its "as drawn" dimension of .800, I get flat sides on the circular webs. I don't understand why. 

I ALSO can see from the blue lines that Sketch 1 is not fully constrained - but I can't figure out what's missing. Every thing I guess and try to add a constraint Fusion tells me the sketch would be over-constrained. 

Can someone tell me what's wrong and perhaps how to fix it? I tried using the timeline but I SUCK at that and couldn't figure out how to get it to help.

[g-andresen]

Hi Greg,

In my opinion sketch 1  is "not very suitable" for the start.

Watch this and/or some other tutorials.

günther

[GregHeumann]

I will watch - I've watched many tutorials on these subjects. I know there are a hundred ways to go about stuff. I could start all over and draw this a different way and know this problem would go away (and possibly create others.) 

But that doesn't help me understand why what I DID do didn't work.  I'm asking here because clearly there is something I did not get. Can you be a little more specific? 

[g-andresen · Accepted solution]

Hi,

give this way a try:

1. start with the sketch of the 1st profile on level 1

2. extruded body 1

3. create sketch 2 on layer 2* > extrude 

günther

* in this case layer 2 is identical to a face of body 1

[TheCADWhisperer]

Sketch 1 is not fully defined?

Why Extrude blocks to make cylinders?

Sketch2 is not fully defined?

Sketch6 is not fully defined?

Sketch7 is not fully defined?

I would do this entire model very differently.

[GregHeumann]

Thanks. I'm sure that would work. 

I DID create a new sketch for each extrusion - just used the box faces to define the new sketch planes and thought I was being clever by using "intersect" mode of Extrude to get rid of the rects. But starting form one end ad working to the other like you did makes good sense. 

[GregHeumann]

I ALSO can see from the blue lines that Sketch 1 is not fully constrained - but I can't figure out what's missing. Every thing I guess and try to add a constraint Fusion tells me the sketch would be over-constrained. 

[TheCADWhisperer]

Use the Origin as you datum.

The first thing you do when setting this up in the machine shop is to define a 0,0,0 datum. Same principle in Fusion 360.

[GregHeumann]

I went back to sketch 1,started with an offset plane at one end and extruded body by body using the newly extruded face to define the new sketch plane. YES - a much better approach and it solves the problem - now the model is 100% parametrically defined. 

I'm still not completely sure why a) my Sketch 1 is NOT fully defined and b) (less important) why the way I tried in the 1st place failed on changing that one parameter. 

BUT - good enough for me - thanks for your help.

[TheCADWhisperer]

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@GregHeumann wrote:

BUT - good enough for me - thanks for your help.

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@GregHeumann 

Don't settle.

Examine the Attached file.

[GregHeumann]

Hi - the cylinders from blocks thing just came to me as an idea to give me two faces to use instead of creating two planes.... which I know I wouldn't have needed to do in the 1st place. And it worked. Sort of. It was just a "satisfy my curiosity" way of trying things in order to learn.

I rebuilt the model from Sketch 1 using @Anonymous's approach above and a) it resulted in a body that is now 100% parameter driven and b) certainly was a more logical approach. 

Thanks for the help.

[TheCADWhisperer]

@GregHeumann 

Examine the file that I attached above in previous response.

[GregHeumann]

That is cool. I've designed other stuff by sketching a profile and revolving it - but the idea to deal with the assymetry by using multiple revolves (and simply revolving rectangles) hadn't dawn on me. That is a great trick and I will use it in the future!

[TheCADWhisperer]

I tend to think and model the way I would out on the shop floor.  (More or less.)

[JamieGilchrist]

Hi @GregHeumann 

here's yet another approach, where I simply used extrudes and your parameters for the distances, starting each subsequent extrusion from the end face of the previous one.  Many paths up the mountain, or so they say 😉

[GregHeumann]

Thanks, Jamie

Yes that is a much better approach and was suggested earlier by @Anonymous - I went back and did it that way and had no issues. 

Cheers

[g-andresen]

Hi,

You can do that.
But the sketches lack the visual assignment to the body.

günther

[TheCADWhisperer]

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@TheCADWhisperer wrote:

I tend to think and model the way I would out on the shop floor.  (More or less.)

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@GregHeumann 

See this example.