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wikiHow to Model a Knife in Rhino

This article takes you through the process of modelling a foldable pocketknife in Rhino. This model was made for Modeling and Prototyping Free Form Product Shapes an elective course at TU Delft.


  1. 1
    Open a new document
  2. 2
    Place background bitmap in top viewport for reference
  3. 3
    Create a new layer called "Handle"
  4. 4
    Select the "handle" layer and start tracing the handle outline using control point curves (turn off snap)
  5. 5
    Use the join command to join all the curves into a closed loop
  6. 6
    Make a copy of the closed curve and move this curve up a few mm in the Y direction, repeat this again but this time move it down the same distance.
  7. 7
    Make another copy of the closed curve and move this up in the same way done in step 6, this line will form a guide for the knife cavity, so this distance will be considerably shorter. Repeat for downwards direction. Delete the original curve.
  8. 8
    Select the top curve and turn on control points. Then move a few control points inwards to create a similar shape as to what seen in the picture at the back of the handle. Repeat identically for the bottom curve.
  9. 9
    Turn on End in the osnap bar and connect the top two curves with a line from this point, repeat for the bottom half.
  10. 10
    Do the same for these parts at the front of the knife
  11. 11
    Now use control parts to drag together these two points (using end snap might make this easier)
  12. 12
    step 12- Take a small break, drink some coffee, have a nap...
  13. 13
    Now select all the curves and use the explode function
  14. 14
    We are now going to start making surfaces, most can be done using EdgeSrf, but others require a 2 rail sweep. The following edges are made with the edge surface function:
  15. 15
    Now make sure you join the following curves again to act as a rail for the sweep you are about to perform:
  16. 16
    Perform a 2 rail sweep with the previously joined curves as rails and the straight line between the layers as a cross section. (repeat for the bottom)
  17. 17
    Perform a similar sweep on the following curves:
  18. 18
    Draw a curve similar to the shown in the screenshot, this curve should be at the height of the top handle curve. Do the same for the bottom.
  19. 19
    Now split the top handle curve using the curve you just added using the split command.
  20. 20
    Use the split curve and the drawn curve as rails for another 2 rail sweep
  21. 21
    Select the following collection of curves on the top surface of the handle (this might require you to explode some previously joined curves. Use PlanarSrf to create a surface. repeat for the bottom. Now the outer shell of the handle is almost done !
  22. 22
    Draw a circle where you want the pivot for the knife blade to be and use this circle to split the two surfaces you just created. Delete the circle surface to make a hole in the surface.
  23. 23
    Extrude the circles into the handle about halfway.
  24. 24
    Use PlanarSrf to make a surface closing the extrude you just made.
  25. 25
    Turn on center snap and draw another circle in the middle of your previous one. This will make the hole for the pivot pin so make sure you keep in mind the tolerances for moving parts. Split the surface and delete the middle circle surface again.
  26. 26
    Extrude this circle to the bottom of your half handle shell.
  27. 27
    Create three new layers, "handle top", "handle bottom" and "blade". Select the top half of the handle and set it to "handle top" and the same for the bottom half on "layer bottom". This will come in handy later.
  28. 28
    Select layer "blade". Switch to top view and start tracing the knife blade using curves as shown.
  29. 29
    Select the blade curve, and copy it. Then move it down about 1mm (which is the minimum wall thickness for a 3D printer. Make sure it still fits between the handle shells and take care you allow tolerances for the moving parts.
  30. 30
    Join the curve loop on the bottom and extrude it upwards to touch the top curves.
  31. 31
    Select the following curves copy them and move these upwards towards the top half of the handle.
  32. 32
    Turn on end snap and draw lines as illustrated below.
  33. 33
    Extrude the back curves to join the rest of the blade
  34. 34
    Use PlanarSrf to close the bottom of the blade.
  35. 35
    Switch to top view and draw a curve as illustrated below. This curve should be on the same height as the top of the blade which is not closed as it will form the sharpened side of the blade.
  36. 36
    Turn on control points and connect the end of the curve with the tip of the blade.
  37. 37
    Draw two diagonal lines from where the blade is extruded to the curve separating the blade. This will form triangles which we can close with a PlanarSrf.
  38. 38
    Close the triangles and the top back of the blade with PlanarSrf.
  39. 39
    Use a Sweep2 to close the first side of the blade, repeat for the other side.
  40. 40
    Make a hole the same size as the holes in the handles in the top and bottom of the blade using split and deleting the circle surface. Do this for both sides naturally. Extrude the hole from side to side.
  41. 41
    Select the whole blade and join it into a single polysurface.
  42. 42
    Select the bottom handle layer, we are going to make a surface that will stop the knife blade from moving when folded open. draw a line as shown.
  43. 43
    Finish the knife cavity in the knife handle. To do this we have to rotate the blade as if it were tucked into the handle. Use the rotate tool to rotate the blade to the desired position around its pivot point.
  44. 44
    Draw a curve that loosely follows the knife outline then join the curves
  45. 45
    Split the following curves using the knife outline:
  46. 46
    Join the curves into a closed loop and extrude this up to the top half of the knife handle.
  47. 47
    Use PlanarSrf to close the handle as shown. Once this is done make sure to split the surface to open the hole for the pivot. Repeat this for the top half of your handle and you are done! All that is missing is the pivot bolt, but that should be pretty straightforward from here on!
  48. 48
    Final model!

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