Constant pitch along an extruded path?


I’m a student studying landscape architecture and a brand new Rhino user, so apologies in advance if this is a basic question.

I am trying to create a curved ramp that must have a constant slope (3.2857%). I was able to create an extruded solid that has the correct width and shape of the ramp, but I am unable to figure out how to cut this so that I have a downward sloping ramp.

(In doing research on the internet, it looks as though people using Rhino for Windows can do this via grasshopper, but I don’t own a windows machine so any other options /suggestions would be really (really) helpful.

Thank you!


ps- I’m attaching a screen shot of what i’ve done in case it helps

(Pascal Golay) #2

Hi DJ- so you’d like the top face of this to have the constant slope, correct? As if it were a path or something?



Yes, exactly; it’s supposed to a path (ramp).

(I think wire cut might be the correct tool, but I can’t figure out how to make the correct plane…)

(Wim Dekeyser) #4

If you do the following on each of the two vertical walls:

  • UnrollSrf,
  • draw the line with the correct slope on the plane,
  • CreateUVCrv of the plane,
  • select the output of the last command and the line that you drew,
  • ApplyCrv these back to the original surface.

Trim the original surface with the new slope curve and when you’ve done that, make the top surface with, e.g. EdgeSrf.

Does that seem right? I am not sure what would be a good way to check the accuracy of this…

Also, the top surface will not necessarily be 100% flat across a section. If that is a requirement, you could try applying the workflow to a center surface.


I am so sorry (and feeling very stupid), but I tried your suggestion and (numerous others) and I can’t get anything even remotely close to a curved ramp.

1.) I am attaching a print screen of what happens with various options for unroll srf.

2.) The one that looks (to my very novice eye) as though it has the best chance of working is the “exploded” option.

3.) I tried various steps with the UVcrv, but couldn’t get it to select properly. I wound up drawing a line across the plane and trimmed it. (I figured this would be a reasonable approximation of the constant slope…)

4.) I can get this shape to wrap (bend) to the curve…

Again, very appreciative of suggestions.

(PS- is there any chance you know the keyboard shortcut for pan in the mac version— (similar to space bar/click/drag in auto cad???)


Hi DJSmith
You must have only one surface and use the command _ApplyCrv
as in the attached file
Ciao Vittorio

Constant_Pitch.3dm(29.3 KB)


Many, many thanks! Not only was I grabbing two sides, but I also had a problem with the original curve not being properly joined (so it was only giving me a portion of the spiral.) I resolved that and was able to generate my first ramp (Hooray!!!)

A couple of comments that may be entirely user error, but I thought I would mention them in case it’s an issue with the mac version (or at least may be different from the way most other mac apps work):

1.) When using the apply UV curve command, I had to select the items /the command at least twice, and in a couple of instances more than twice before I was given the option to apply it to a surface. (I looked at a number of online videos and they don’t seem to have this on the windows side- it seems to happen automatically via stepping through the command?)

2.) For the life of me, I can’t figure out to get to a sequence to use my mouse to pan— I keep having to up to the top ribbon.

3.) I can’t get copy and paste to work across multiple documents…

Thanks again for all of your help…