# Create a curved circle with precise dimensions

If you imagine the external edge of a torus, all the way around, or you imagine a uniform cylinder where you then bend the vertical edge in uniformly to create a circle - that is what I'm trying to achieve. A curved circle with specific measurements.

Specifically, I want it to be 4 units high (easy) with the swell of the curve precisely one unit thick. In other words, say the bottom of the curve is at 0.00, then the widest point of the swell is at 1.00 before coming back in again to 0.00 at the top of the curve.

I imagine this could be done by trimming down a torus, but the "exterior/interior" radii settings on the Torus Dimensions don't appear to be accurate enough for my purposes - because the Torus inner edge swells in too, and I can't therefore use that to measure because I don't know the degree of that swell.

I imagine this could be done by bending a 4-unit-high cylinder, but I don't know how to...

Any help/guidance much appreciated.

Thanks, A

• A sketch / screen grab might still help understand exactly what you're after .. Jun 21, 2019 at 10:08
• Done that...,,, Jun 21, 2019 at 12:33

Depending on what profile you'd like, for example:

1. Semicircular, in which case the width has to be 2 if the height is 4
2. Elliptical, scaling the semicircular in X
3. An arc of a circle passing through (0,2), (1,0) and (0,-2)

You can create the surface of revolution from them

• destructively, by using Alt R, the spin tool, adjusting settings for center and axis
• or non-destructively, by assigning a Screw modifier to the profile, with 0 'Screw' setting.

For version 2, looking down Z:

• ShiftA create Mesh > Circle, 32 verts, then, all in Edit Mode...
• X delete half the vertices, retaining N & S poles
• SX0.5 scale to a half-ellipse
• GX move the mesh with respect to its own object origin to get the desired major radius. (By default, the modifier will rotate around the object origin)
• Assign a Screw modifier, as shown.

The advantage of using a modifier is that you can still make adjustments to the mesh in Edit Mode after assigning it, and see the results.

• If you need more detail on a particular version, let us know Jun 21, 2019 at 15:05
• Yep, this is perfect - I'd like a number 2, please. How do I make an elliptical curve like yours (with exactly 17 divides, incidentally)? Jun 21, 2019 at 15:51
• @Altissimus.. Done that.. :) Jun 21, 2019 at 17:36
• many, many thanks. However, the main problem now is that it looks so much better than what I had before I am going to probably end up changing a bunch of stuff.... which means I also need the same thing in a straight line. Is there a modifier I can apply to the curve (instead of screw) that will allow that? Jun 21, 2019 at 19:38
• This is really another question, but to get you kicked off, for a straight line, just E extrude the profile.. you can also send it down any path you like.Look up the Curve modifier. Also consider the possibility of converting the profile to a curve, and using it to bevel another curve. If you get stuck, by all means post another question. Jun 21, 2019 at 20:23

A curve with its control points precisely placed and a Screw modifier will do this.

Is this the shape you wanted?

Edit:

Sometimes the handles get swapped around, and that kinks the curve around on itself. So move the handles around and see what effect that has on the curve to make sure they're coming out on the right sides. If you move the control points (the handles get highlighted too) with G for grab, X, Y or Z for the axis and 0 or 1 or whatever you need, you can get them in a symmetrical place - you have control over that at least. To get the handles arranged you can turn on Snap (the magnet icon at the bottom in Blender 2.79) and turn on Absolute Grid Alignment (the second icon along after Absolute Grid Alignment, you can move the handles to a fixed point on the grid so everything is properly aligned and symmetrical. If you then want more or less curve you can move the handles to another grid point, keeping them symmetrical.

• @cegaton Aaah! So that's why. OK. Jun 21, 2019 at 15:13
• So this makes sense but getting that Bezier curve to look "how I want" is just as much of a problem as the original problem. Moving the handles can't be done by insetting numbers; when I put it to 0 degree of 90 degree rotation it's actually twisted something wicked - clearly I don't understand what the point of reference is for the angles the handles use, even though my pivot point is at 0,0,0. Also, no way of controlling exactly the shape formed afterward. Jun 21, 2019 at 15:51
• I've added a comment on handles in the answer above. Jun 21, 2019 at 21:34