Best method to use the Curve tool for complete shapes?

[ben2ek (Brian)]

I am looking to create a similar table to the iconic Noguchi coffee table that features a triangular shape with differing rounded corners. That shape lends itself to the Curve tool very well, but I cannot for the life of me create a completely convex (no inward facing edges/nodes) shape using the curve tool alone. I always end up with one concave node. I’ve tried this in Carbide Create as well as the Bezier tool in Inkscape. Inkscape offers a little more flexibility in editing and rearranging the nodes as well as some “Simplify” tools to smooth things out, but in the end the shape ends up still having odd bumps, lumps, or other imperfections.

Is there a best practice for getting a completely convex shapes using the curve tool?

The screenshot below is my attempt (pink line) at recreating the traced image that I uploaded from a a google image result (black line) which did a really good job at tracing, but still had slight imperfections on some of the corners. I just needed it to be close-enough, not a perfect match.

My method I used was to start the curve in the middle of the edge, select a point close to the center of the rounded corner, click and pull the curve to match the curvature of the traced image, and then find another mid-point along the next side of the shape that matched the curvature, then click to end the curve. I tried numerous other methods and starting points but they all produced similar results. It seemed like as I pulled the curve to match the shape, the curve “dipped” below the starting node at a certain point which caused the concave node to form.

CC file attached.

My best attempt:

Concave node:

table_v1.c2d (112 KB)

[Jeffish (Jeff de Ruiter)]

An offset vector would give you the exact shape of the original. No node editing required…

[WillAdams (William Adams (Carbide 3D))]

Like Nike says,

Just do it.

Start by sending things to a locked layer and turning off snapping:

Normally nodes are placed at extrema (top/bottom, left/right), points of inflection (middle of an S — not applicable here)

click on the first point to close:

Then, go into Node Edit mode:

and smooth and adjust as needed:

Zooming in at need:

and if need be, using a cusp node so as to have uneven lengths:

If need be, add additional nodes:

Eventually arriving at:

Attached as a v8 file.

table_v1_v8.c2d (116 KB)

[WillAdams (William Adams (Carbide 3D))]

If you want things offset from that, then as noted, “Offset Vectors” will work:

but creates a polyline:

[WillAdams (William Adams (Carbide 3D))]

Or, if one wants a 1 inch offset:

table_v1_v8.c2d (116 KB)

[Tod1d (Tod (with 1 'd'))]

I generally try to place nodes where there is an obvious change in curvature.
The last node connecting to the first is impossible to get tangent. I just click on the first node so they join automatically, edit the nodes, select that node & hit “S” for smooth then adjust the tangent vector.

[ben2ek (Brian)]

Incredible, thank you!