[Rayne]

Subtract always works. It will do it's thing or crash radiant.
Make sure you only select the brushes you wan to use FOR subtracting. But not those you wish to subtract from.

[MajkiFajki]

Ok - try by yourself:)
I selected smaller brush, pressed button and still nothing :(

[FS HappyDay]

I guess you want something like this? Here's the map file.
Actually this is a very messy way to do that. If you want to do it in a 'clean' way you have to use 2 cylinders that fit together. For this kind of stuff I highly recommend Rambetter's surface generators, no CSG substract, no bobtoolz.

[MajkiFajki]

@Happyday

Thanks. But I don't get perfect surface:

[FS HappyDay]

I don't know what you did there. You can get as smooth surfaces as you want. However, if you enter the wrong values you might get no brushes at all or a faulty surface because it's impossible to build.