Circular ramps

OK, I did'nt notice any search parameters on the editing forums, and I tried the default search engine on the top of the main page.I'm trying to expand my knowledge of shapes, and how source deals with them, and I'm trying to make a smooth circular ramp, not stepped, but gradually ascending. I remember asking reaper about his meticulous work on the spiral stairway handrails, which he said were all on the grid. But for the life of me, I cannot get the same thing to happen without invalid brush errors.
I start with an arch, 24 sides 360 degrees, wall width 60w and 8h and create object.
I have tried for hours using the vertex manipulator, but to no avail. I know I can use displacements, but I would have to make a top and a bottom, and that seems kind of excessive. What amI missing in this most basic of shapes? Any input would be appreciated.

You get the invalid brush error from a face that is not flat. A face can be tilted at different angles, one side can be lower than another side, but if the face isn't flat, your in trouble. For example, create a simple rectangular prism brush, open up vertex manipulation and raise one of the corner points at the top, just one corner. The brush you now have is invalid because the top surface is not flat.

Here are some things I know about how source deals with BSP geometry:

-Everything is split up in triangles.
-Surfaces are cut up depending on the texture resolution and scale and the light map scale.
-World geometry touching eachother will split the faces.
-Func_detail and like do not split faces.
-BSP geometry is quite demanding compared to mesh/model geometry.
-Probably more that I have forgotten.

I have no idea how I would create what you want, but I would try two things.

1) Try screwing around with the arch tool but I still don't know how it works properly.

2) Create a 15 degree section of the spiral you want, (set default rotation to 15 degrees in 2D options), than [Shift] + drag that segment around, rotate and put in place. If you do that and you have a triangular gap (depending on how you made your original piece) than just create a new brush and fill in the gap.

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Aaron's Stuff

The inside edge of a spiral ramp has a steeper gradiant than the outside edge, so to make it smooth, it would need some sort of twist in the middle, and we all know hammer doesn't do twist, it only does stupid triangles.

So the triangle version would look something like this,

Hey Juim, if you haven't seen this

http://www.hl2dm-university.com/forum/phpBB3/viewtopic.php?f=5&t=1439&p=16778&hilit=spiral+ramp+tutorial#p16778

basically triangles, as above

http://developer.valvesoftware.com/wiki/Hammer_Arch_Properties

Maybe that will help?

Or you can model it with blender.