I can't achieve getting a mathematically exact helix with constant radius and progressive pitch.

I tried wrapping an arch (with the exact pitch progression I want) around a circle with the correct diameter of the helix using the flow tool, but resulting helix isn't accurate.

In some places the helix doesn't match the radius it should have, accuracy is off by a few microns. Also, points of interpolation are not evenly distributed (maybe this is having some influence). See attachments.

I also tried using the variable pitch helix plugins made by users but results aren't mathematicaly accurate either.

Why doesn't MoI3D allow making a mathematically exact helix with constant radius and variable pitch, if AFAIK it allows making mathematically exact circles and archs? This was with MoI3D V4, I haven't tried with V5 yet.