Grinding a twisted shaft - GIF

Grinding a twisted shaft.

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Previously:

https://www.homemadetools.net/forum/...836#post223738
https://www.homemadetools.net/forum/...085#post141180
https://www.homemadetools.net/forum/...070#post141064
https://www.homemadetools.net/forum/...909#post108922
https://www.homemadetools.net/forum/...577#post209211

That's a rotor for a progressive cavity pump. Long ago I worked for my uncle that had a drywall spraying equipment manufacturing company. We used to make those with hydraulic tracer lathes...
https://www.youtube.com/watch?v=_4nnTp1fvqg

Mono pumps use something similar with a flexible chamber to pump water/ slurry with suspended solids. - last saw one in the mid 1990s at an ag show for pumping dirty water.