Tangent Constraint Frustration

[walrys]

01 (see attached 01.jpg)

I'm using some simple sketches to first create a block, then cut out a couple of channels before applying a variable fillet along the entirety of the bottom edge of the channel.

FIG_02 (see attached 02.jpg)

To give myself some flexibility as I work I've attempted to set up a way in which I can vary the width of the channel by altering the diameters of the circles and have the connecting splines adjust accordingly via a tangent constraint.

I hesitate to call out BUG! but this was an incredibly frustrating thing to accomplish - the software behaved erratically even when the methods used were repeated exactly (ad nauseum) ie. sometimes the circles would slip about despite being constrained concentrically to the construction circles, sometimes the tangents would stick at one end but not the other - a total mess, but eventually something stuck...

FIG_03 (see attached 03.jpg)

BUT - at certain sizes I can't select a portion of the model without selecting the rest of the block with it - some sizes do work, but not the ones I want to work!

I had a look around and found this old thread about the tangent constraint not really being a tangent constraint:

https://forums.autodesk.com/t5/fusion-design-validate-document/tangent-constraint-is-not-working-cor...

The thread mentions using the tangent constraint along with the coincident constraint, which I have tried to no avail.

I also came across this thread:

https://forums.autodesk.com/t5/fusion-design-validate-document/tangent-sketch-constraint-problem/m-p...

...and it states that "Fusion does not support tangency to a spline curve (except at the ends of the spline)" - which could very well be the root of my issue here, but if that's the case why does it sometimes work..?

I'll upload my project file below. To recap on the general idea of what I'm trying to achieve:

To independently alter the diameters of the circles in the sketch and have the tangential curves update accordingly. (I've managed to set this up, it behaves in a somewhat flaky manner, though).

Once back in the modelling environment I'd like to be able to select the channel areas and cut/extrude into the block before applying a variable fillet along the entirety of the bottom edge.

Any advice appreciated!

Wal.

[walrys]

Project file attached.

[laughingcreek]

before getting to deep into this, I'm curious about how you drew the splines.  if you right click on aspline and select "display control frame"-

you can see the spline is actually a series of 3 degree control point splines connected end to end. (you can tell b/c every 4th point is on the spline, and if you drag one of those you points you get something like this)

I have only seen splines like this as a result of importing a curve, projecting into sketches, or changing the degree of a control point spline after creation.  hence my curiosity about how you managed to produce this spline.

in any case I did see that there seems to be a bug.  usually when you start a sketch curve on another sketch curve, if you click while there is an x showing, an automatic constrain will be applied.  this isn't happening in your sketch.  I'm attaching a screen cast of that happening.  I couldn't reproduce this in a new model which is weird.

these types of splines are difficult to control, so I suggest deleting all the splines and creating clean ones.

fully defining the sketches will also help tame them and keep things from jumping around unexpectedly

. 

actually, are splines necessary?  it seems like arcs would be better.

might also be better to put the rectangle and the circles and splines/arcs in different sketches also.  will be easier for fusion to track the profiles used in feature creation.

[laughingcreek · Accepted solution]

here's an example of how I might approach the sketching.

[walrys]

@laughingcreek- that's very nicely put together, thanks for taking the time.  It'll take me a while to unpick, but it seems to work very well.

To answer your question on how I drew the splines - I imported a DXF and offset the two splines that I later tried to tangent constrain.  Hmm - that's probably not doing me any favours...  😐

Thanks again for your input here.

Wal.