Could you upload your file?
you will not be able to create a flat plane from 3 lines.
if all 3 lines are already on the same plane, SW will reject the 3rd line.
however, if the 3rd line is not on the same plane, it will add it and create a curved surface, to force them to fit.
this may be the reason you are getting a curved surface.
You could offset a plane from the base face and set it tangent to one of the inner/outer edges.
Otherwise just sketch a line on the plane that bisects the angled cut attached to the high/low tangent points and cut with surface. close enough judging by the views provided.
If I understand your question correctly, this is how I'd do it. I'm not sure about the nature of the cut you have, so I just approximated something that sort of looks like yours.
- Sketch on a plane that goes through the centerline of the cylinder.
- draw the black line from midpoint of upper angled edge to the midpoint of lower angled edge
NOTE: in my model, there's some problem. I can't get the lower edge to project into the sketch plane, or make any sketch relations to it.
- Draw the blue line perpendicular to the black line
- Make a plane through the blue line perpendicular to the sketch plane
- If you want to extend/trim the cut face of the cylinder to the new plane, make a planar surface on the new plane and use the Replace Face feature, which will both add and remove material to give you an angled but planar end face.
Part2.SLDPRT.zip 112.6 KB
Thank you very much Matt, for taking the time to write this detailed answer!
And thanks to everyone in this thread for helping!
To build on Matt's approach...
You could create a 3D sketch and use convert entities on the outer or/and inner edge. At least with my approximation of your model, this created an ellipse with a VERY convenient point entity at the lowest point (circled in red).
From that point I created some reference geometry:
- A line [LINE 1] from the circled reference point to approximately the highest point on the ellipse.
- A line [LINE 2] coincident with the axis of the cylinder
- Set the Mid-Point of LINE 1 coincident with the End Point of LINE 2 - This could probably be done with an axis in place of LINE 2
- Set the opposite end of LINE 1 coincident with the ellipse
- This caused errors in my sketch - I expect there is a slight geometry mismatch but I did not dig into it
- As a work around I added a point and made it coincident with both the ellipse and LINE 1
- A line [LINE 3] perpendicular to LINE 1 and coincident with LINE 1's mid-point
- A line [LINE 4] with endpoints coincident with LINE 3 endpoint and LINE 1 "circled" endpoint.
- A point made coincident with both LINE 2 and LINE 4
- If you wish, make LINE 2 and LINE 4 perpendicular to fully define the sketch.
From this you can create a plane by selecting the endpoint of LINE 3 as well as LINE 3. This plane will be "IN PLANE" with the ellipse. From there you can replace face, cut with surface, etc.
NOTE, this entire approach relies on the automatic creation of the lowest point of the ellipse. No need to determine any angles, dimensions, etc. Not necessarily better, just an alternative means to the end.