Conical spiral construction

[themole]

hi, I have this problem : I have to build a dx spiral with starting diameter 280 for 120 mm then widens with a 45-degree angle for 33 mm becoming of diameter 327 mm for about 257 mm.
the pitch is 250 mm.spessore 35mm.
practically wraps around a total length tube 410 mm.
Does anyone help me?

grazoa

 

[mir]

I would do like this:
1. I create a spiral
2. I create a cone of subtraction to "cut" the spiral and make it conical

:

 

[Therapy?]