Filleting 3 line 3D sketch problem

Hello

I have been trying to find the right technique for achieving the
following.

You have two random straight line ends in 3D space. The end points are
fixed and can not (should not) be moved. You want to link the two line
ends up using the following:
- two tangent arc elements (one for each line end)
- one straight line (to join the free ends of the two tangent arcs
together and complete the smooth tangential chain)

This can not be done using 3D fillet command as the end points of the
lines will be shortened and the original location for the line end
points will now become the location of the "virtual sharps".

I am finding that manipulating the 3D tangent arcs to be difficult.
They have three degrees of freedom.
1. Rotation angle about line end
2. Radius
3. Arc length (or arc angle)

SW is not able to automatically solve the sketch if you try and rely on
adding relations only (even without any dimensions being defined).
Perhaps you need to more closely geometrically approximate the answer or
perhaps there are just too many variables that it can't solve them all
at once.

Is there a fail safe efficient technique for ensuring a solution?

Bullman

 

It's impossible to have a 3D fillet feature, I think you can connect
this kind of 2 space line segment by 3D spline. after draw the spline
on any plane, you can add tangent relation to found a "3D fillet".
You need to use other spline tools to fully define it, to make it looks
like a fillet.

 

Got an idea. Workng on it. Be back in a day or two.

 

What I would do would be to turn the original lines into construction
geometry, draw new lines and arcs in space disconnected from the
original lines, and then once the tangent relations are working and the
shape is approximately correct, drag the new lines/arcs onto the old
construction lines.

Or, just draw the line connecting the endpoints, make 2 reference points
at random locations, then key in coordinates to put them at the
endpoints of the lines, then fillet the corners and drag the moved
endpoints back to the reference points.

Another thing you could try would be to leave the original lines alone,
draw the 3rd line, build sketch planes using the 2 endpoints of the 3rd
line and the end point of an original line that the arc is to hook up
to, and then you have planes for the arcs. Of course the new sketch
plane function in 2006 is pretty fragile, and pretty likely to fail.

Or you could just say "screw it" and put a couple tangent splines in
instead of arcs. You'll solve one set of problems and create another
set.

There's not much in a 3D sketch that is what you call "fail safe", and
because you're usually working with workarounds, nothing's really very
efficient either.

good luck,

matt

 

Yes, if you don't care too much about the fillet radii.

 

Yes, but don't always count on the fillets haveing the same radius.

 

Yes, at least from a geometry standpoint it works except for two
special cases one of which you probably will never want to try.
However, SW gets quirky when implementing this.

 

Yes, but......you can't always get the fillet radii you want.....it
doesn't work when geometrically impossible.....and SW gets a bit quirky
even when it is geometrically possible.

 

Paul,

Was that "turkey" or "Wild Turkey" that you were getting into? I see
that you're responding, but what are you responding to?

Matt

 

I tried to respond when the post first came out. Nothing happened so
posted again. Then today they all appeared at once after That 70s Tick
responded. I was responding to Bullman's post.

 

<http://www.esoxrepublic.com/models/>
Look at model "SkewFillet.SLDPRT"
First sketch is two skew (non-intersecting) lines.
Second sketch connects skew lines w/ fillets and line in middle.

Key elements: Sketch points coincident with original lines and middle
line keep middle line intersecting the two skew lines so a fillet can
be applied. Fillets were created by creating temporary construction
lines collinear with original lines.

 

Similar to the construction I had. But.....just like mine it doesn't
like having the first sketch changed. I doesn't want to solve. I used
2D planes in 3Dsketch to hold down the 3 point arcs. You can put all
the geometry in one sketch. It still doesn't update very well.

 

Another stab. More complex, yet more robust, yet more complex. Pairs
of dimensions in "Midline" sketch need to match to produce dependent
fillet of equal length.

 

Suppose I should post the file location:
<http://www.esoxrepublic.com/models/>
SkewFillet2.SLDPRT

 

One thing is apparent. The constraint solver in 3D Sketch doesn't work
very well, even in 2006. I have used the second method when reverse
engineering imported CAD geometry. Sticking with planes and 2D sketches
is pretty robust.