Technodandy Posted February 24, 2006 Share Posted February 24, 2006 When I cut a circle, I created with lathe, in half it does not keep it symmetry about the center. It bows into a parabola instead of keeping it's half moon shape. I then have to staighten it out slowly by hand, one Control point at a time. Anyone know a solution? Quote Link to comment Share on other sites More sharing options...
Stuart Rogers Posted February 24, 2006 Share Posted February 24, 2006 There are two solutions: add more CPs to define the curve, or play with the gamma and magnitude settings of the existing CPs (particularly the end ones). OK, so there's a third option... Create your half circle, lathe it to make a sphere, and then start disconnecting (but not deleting!) CPs in the section of the sphere you don't want. Quote Link to comment Share on other sites More sharing options...
MMZ_TimeLord Posted February 24, 2006 Share Posted February 24, 2006 I usually use the last method that Stuart mentioned. I lathe my circlular object then I remove part of the side I don't want and break the splines so there is one branch of the circle remaining on each side of the half I cut. That way the curve remains unchanged. Edit: Here's a screen shot of a quick 8 lathe sphere. NOTE: on this particular 8 lathe sphere, I could delete the 'tails' that remain without distorting the remaining half. On a 4 copy lathe it will distort unless you leave the 'tails'. Most times if the number of lathe divisions is 8, 12, 18, etc. somthing that allows it to have a seam at the axis you want to cut it on, you should get very little distortion. At least the way I make spheres. The technique I use is to lathe a 2 point spline with 8, 12, 18, etc. and delete the half that is off the axis, rotate it 90 degrees and delete half of it. Move the two points on the axis that remain just one 'nudge' with the arrow keys to the side your half circle is on. THEN lathe this spline... you should get a nearly perfect sphere (minus the ugly pinch points in the north and south poles). This is the type of sphere I have cut in half here. I've attached another screen shot compilation showing how I build the 8 lathe sphere... WARNING: The compilation is nearly 900k in size! Quote Link to comment Share on other sites More sharing options...
heyvern Posted February 24, 2006 Share Posted February 24, 2006 Holy crud... I never would have thought of that... I am too obsessive! I would never even consider leaving those hanging splines! I always just use more points. a low patch half sphere... nice. Vernon "!" Zehr Quote Link to comment Share on other sites More sharing options...
MMZ_TimeLord Posted February 24, 2006 Share Posted February 24, 2006 Another item of note... I believe I found what way Technodandy was cutting his sphere. If you cut across the 'Y' axis, then you will have a parobolic dish as he said, unless you leave the 'tails' like this. If you cut along the 'Y' axis, as I did in my first example above, you should see no distortion. You are left also with two sides that are not perfect (i.e. - pinch spots). Where in his cut, you will have only the one pinch spot to deal with. There are many ways to get a near perfect half sphere. There are many ways to get a near perfect sphere too. The way I do a near perfect sphere is this. I make a sphere, and cut off the poles. then copy and paste it (with no offset) and rotate it 90 degrees on the 'Z' axis. This results in the appearance of a perfect sphere. The downside is if you have to decal it, you may have to do two 'stamps', one for each partial sphere. I have also attached a wireframe and shaded wireframe of this type of sphere for your info. I made each partial sphere a different color to show what is happening. Quote Link to comment Share on other sites More sharing options...
Kamikaze Posted February 25, 2006 Share Posted February 25, 2006 Damn, you mean there is no key you can hold down to maintain curvature while deleting splines ...........Smile............... Michael Quote Link to comment Share on other sites More sharing options...
Technodandy Posted February 25, 2006 Author Share Posted February 25, 2006 Damn, you mean there is no key you can hold down to maintain curvature while deleting splines ...........Smile............... Michael Exactly the solution I was hoping for Michael but the other solutions will work to eventhough they are not as straight forward as I would like. Thanks everybody, but if anyone knows if there is some key for maintaining curvature please let me know. Quote Link to comment Share on other sites More sharing options...
mtpeak2 Posted February 25, 2006 Share Posted February 25, 2006 I'm not sure I understand what you are trying to do. I think you are missing a step when deleting half the circle/sphere, there's no need for dangling splines, unless I'm missing something here. After lathing your circle/sphere and deleting half of it, you need to break the spline that AM keeps to continue the loop (it depends on which half you are deleting, side or top/bottom). You can also select half the circle/sphere and copy/paste it. If you are trying to close the flat side, you need a 4 pt spline, using the 2 middle cp to close the loop and deleting the ends after you attached the cps. Quote Link to comment Share on other sites More sharing options...
Technodandy Posted February 25, 2006 Author Share Posted February 25, 2006 I'm not sure I understand what you are trying to do. I think you are missing a step when deleting half the circle/sphere, there's no need for dangling splines, unless I'm missing something here. After lathing your circle/sphere and deleting half of it, you need to break the spline that AM keeps to continue the loop (it depends on which half you are deleting, side or top/bottom). You can also select half the circle/sphere and copy/paste it. If you are trying to close the flat side, you need a 4 pt spline, using the 2 middle cp to close the loop and deleting the ends after you attached the cps. Hi Mark, That was it. I new it had to be something simple. I was just one step away from doing it right. Thanks, Technodandy Quote Link to comment Share on other sites More sharing options...
mtpeak2 Posted February 25, 2006 Share Posted February 25, 2006 Glad I could help. Quote Link to comment Share on other sites More sharing options...
Kamikaze Posted February 25, 2006 Share Posted February 25, 2006 Cool...mtpeak2................ Michael Quote Link to comment Share on other sites More sharing options...
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