The splitted tutorial is obsolete, so you are advised to look to unique tutorial here https://grabcad.com/questions/how-to-model-a-centrifugal-pump-body-spiral-construction-using-inventor-2014
A half-plane section of the main part body is presented in the image. The special construction consists of its internal and external „circular” body, which is actually a spiral one. Trying to use the Loft feature for creating this feature must include a spiral centerline, after selecting the normal sections represented by 2D sketches.
Another problem is that the internal (void) body seams to be difficult to model when the external (consistent) body is present. To solve this particular problem, the proposed approach is to begin by modeling the internal body as a first solid, then modeling the external body, and ending with subtracting the internal solid from the external one. The solution is generally welcome for parts with complicated internal void features.
Read the attached pdf file.
Note: This tutorial is splitted in 8 pages. You can collect all that 8 PDF pages and print them to have a printed material. There is a way to gain the PDF with all 8 pages if you read below.
As mentioned above, the splitted tutorial is obsolete, so you are advised to look to unique tutorial here https://grabcad.com/questions/how-to-model-a-centrifugal-pump-body-spiral-construction-using-inventor-2014
WER IS PAGE 4/8??
This is an obsolete partial tutorial.
You have to see the full presentation here: https://grabcad.com/tutorials/how-to-model-a-centrifugal-pump-body-spiral-construction-using-inventor-2014