how to create conic radius? 1

[phbalance]

How do I create a conic feature in sketcher? I need to make a radius'd corner using a conic instead of a round blend. The shape is basically a tall rectangle, with one side having a slight arc. When I try to constrain the conic in the sketch (tangent to the arc and line and coincident to the same arc and line), the sketch turns either yellow or red. The same happens when I try to place dimensions.

 

[cowski]

Hard to diagnose without seeing the sketch.

However, I will offer up a "plan B". Would it work to make the corner sharp, perform the extrude (or revolve, sweep, whatever) then use the face blend to apply a conic section blend?

 

[ewh]

I agree with cowski. It usually is easier to edit blends when they are created outside of the sketcher. Why make things more complicated than they need to be?

 

[phbalance]

I tried what cowski mentioned. The part is basically a 1/4" thick, quarter-circular tube (6" radius x 10" high). The one side I am trying to apply the conic to is arced (not straight). Because of its circular xsection, face blend seems to be limited on how dramatic the conic can be. Maybe I'm not using the face blend right. With a sketch, it should be easier to create by simply cutting it away.

 

[phbalance]

Okay, I found a way to do it. Sketch 2 unattached lines. Then use "bridge curve" to connect the 2 lines together. Then extrude the new curves.

That was easy...

 

[cowski]

Easy as long as you don't need a true conic section...

 

[Xwheelguy]

If you're not getting what you want with the conic Face Blend, then you need to adjust the Rho value. Increasing the value makes the conic blend more pointed, while decreasing the Rho value makes the blend more flat. The Offset values just control the tangency lines (overall size of radius).

If you are familiar with Bridge Curve, then just use the numerical values in a similar manner for the conic Face Blend.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

 

[PhilJenkins]

To correctly constrain a conic in sketcher, you need to create two construction lines. Eg. if you want a conic to run tangent between two arcs then you need to extend a construction line tangent from each arc end point in the direction of the conic and trim the two construction lines where they intersect each other. Then draw the conic using the end points of your two arcs and use the intersection point of the two construction lines as the conic's anchor point. The conic will then be fully constrained (assuming the original arcs and construction lines are) and tangent to each arc. Use edit curve to adjust the rho value of the conic. It's not very intuitive but works extremely well when applied correctly.

 

[phbalance]

Thanks PhilJenkins for the response. I guess I was constraining the conic to solid lines instead of construction lines. It makes no sense why UG can't differentiate the 2 line types, but it worked.

 

[PhilJenkins]

By using the construction lines in the manner I described you are defining the anchor point of the conic in a way that ensures tangency between the conic and the arcs. The conic itself has no tangency constraint with the arcs but because the two construction lines are tangent to the arcs and the interscetion of those lines defines the conic anchor point then by definition the conic has to be tangent to the arcs. Why NX won't just allow you to place a tangency constraint on each end of the conic and have a free anchor point, I don't know. That would be the intuitive way to deal with it.

It took us several days of trial and error to figure this out. UGS were no help whatsoever - all they could suggest was to create the sketch minus any conics and then use bridge curve to create the conics afterwards. That approach is OK if you know beforehand exactly what shape you want, but in our business where we want to be able to manipulate the shape in sketcher and see how small changes will affect the appearance of our products it's just not workable.