Help drawing an Impeller

[patt.t.klein]

Hi everyone,

I'm planning on building myself a new dust extractor for the workshop.

I stumbled across this (https://www.google.com/patents/US6632071) for making an optimized blower impellor based on a modified Archimedes spiral design which is supposed to have better efficiency and lower noise. 

The document has a step by step guide on how to draw it up, yet I am still having some difficulty. 

I have drawn a curve that is quite close to the recommended curve as a sketch. however I don't know how to trace a slot along that curve. I would like to make a 3mm slot along the line and then circular pattern the slot around the disc then CNC the disc to asemble it. 

Is anyone able to help tell me how to turn the line into a slot and or a better way to draw the curve other than using a combination of the 3point arc tool and the spline tool. 

I have added some photos. 

SketchImpeller design

Thanks! 

[davebYYPCU]

Sketch > Offset, 1.5mm each side, use 2point circle to close the slot ends.

Might help...

[patt.t.klein]

Cool that worked for turning the lines into slots! Thank you. 

Now I just need to work out how to draw the curves properly. 

[davebYYPCU]

Spline will do it nicely, use two or three points from the grid, and pull the Tangent Handles to fit the curve.. 3 point arcs have to be made Tangent to each other, both work about the same.