Okay, way too long since I had to calculate something like this so I need a basic math check.

I'm designing a large tub mixer for doing 2 - 2.5 cubic yard batches of concrete and for the tub mixer paddles I am going with a simple single turn helix of 3" x .625" steel bar stock. Being it has to both mix and push the wet mix to one end to unload it needs to have a helical shape to it.

So here's the dimensions.

The tub is ~38" dia by 66" long and I need the single bar to make a 360 degree arc in that 66" distance.

My rusty off the top of my head math says that the bar stock to make that helix paddle needs to be ~ 132" long and the online calculators agree but I feel like I am missing something in the equation relating to the bar dimensions affecting the clearances which I need to be about .5" on each side and end that the basic online calculators don't include.

Oh yea and if anyone wants to nerd out the rough math on torque to spin such a pair of them 180 degrees apart though dry 3:2:1 base concrete mix I would be curious to see what you get for theoretical worst case scenarios so I know what sort of power I am going to have to shoot for based on a ~30 RPM mixing speed.

I'm guessing 3000 foot pounds minimum but I may be way short at that in realistic operating terms.

## Comments rated to be "almost" Good Answers:

Re: Need a design math check. Length of helix." by SolarEagle on 11/12/2016 9:13 AM (score 1)