Surface Creation On Non Planer curves

I am a high school shop teacher and have been teaching myself Rhino 4 for many years now, slowly building to 3d. I know a little but need some help. The project I am working on is making a belt buckle for sandcasting so all the sides have to be tapered 5 degrees and all corners filleted. I am going to machine this on my CNC mill or get it 3d printed.

My problem is I don’t know how to create a surface that is curved without splitting it from another object. So far I have done in step:

  1. Created a 4" x 2.5" elipse to make the overall shape of a standard oval buckle
  2. Off set the oval inwards 0.25" to create the inner portion were text and designs will go
  3. Created a 36" cylinder and split out a portion of the cylinder to create the curved surface I wanted, this gave me an the oval curved the correct ammount.
  4. Split out the center portion of the new surface at the 0.25" offset curve for the text and designs
  5. Created curves from dulipacting border to make curves I can snap to.
  6. Extruded curve tapered 5 degrees to create the outer edge of the buckle and inner edge where the text and designs will go forming a 0.125" depression

This is where I am stuck. I need to create a curved surface to make the bottom of the depression and the same but for the bottom of the belt buckle. I tried 1 rail revolve but the result is less that desirable. Patch works and creates the curved surface in the x axis but it is curved in the y axis as well not flat, in other words it is dished, not curved.

Here is the file if you can help, it is greatly appreciated:

Hi Kevin-

  • Make a copy, in place, of the outer rim - your initial cylinder,
  • Start Split and use the curve at the bottom of the .125 inside wall to split the cylinder. You can DupEdge to get the trimming curve or use the ‘crv’ filter when Split is asking you for the splitters and then pick that lower edge.
  • Delete all but the center ellipse from the split object.
  • OffsetSrf, Solid=No the split out center .125 downward.

Is that what you need?

Surface Creation Help_PG.3dm (199.3 KB)


Hi Kevin,

Good start - Here’s a simple workflow: circle, oval, a few offsets & extrusions, trim/split & join.
36 circle, offset inward .125 & .25 (my guess for the buckle thickness
4 x 2.5 oval, offset inward .25
extrude outer oval, taper 5 degree draft
extrude inner oval, taper -5 degree draft
surface, extrude all 3 circles, straight; top rim, back and inset
trim inner and outer walls w/top, back and inset
trim top, back and inset w/inner & outer walls, join
Kevins buckle.3dm (230.9 KB)

Best regards,

Forgot to add that you can use the same approach for adding text or simple silhouette-type of design. Create as curves, then extrude with the appropriate draft angle. Also, if the draft angle comes out incorrect in the above example, change the positive draft number to a negative number, and vice-versa.

The top surface (rim of the buckle) and inset surface can be used to split the type/design extrusions, in a similar manner as the buckle blank was created.

Good luck with this project, sounds like fun for the students!


Thank you for your help, I will attempt to follow it as best I can, sadly I cannot open the files as I assume they were made with Rhino 5 and we only have Rhino 4. If there is a way to resave them to my format it would be greatly appreciated.

I believe Kevins buckle.3dm is a V4 file.
Here is Pascal’s as V4: Surface Creation Help_PG.3dm (301.7 KB)

You could also download a demo copy of Rhino V5, open the files, and use SaveAs to V4 files.

By the way, you can upload your files here directly by clicking the upload icon in the Create Topic or Reply window.

Well, shoot. It wasn’t like you hid the fact you were working in Rhino 4… Anyway, here it is, saved as Rhino 4. Sorry for the inconvenience.


Kevins buckle V4.3dm (252.5 KB)