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RPM for star roller?


gdeputy

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I'm looking at building a star roller from scratch, using a worm drive motor like one of the these. I can control speed pretty easily and they SAY they're high torque. Anyone use one before? What would be an ideal RPM? They're available from 5-100 RPM, and i'll be able to control the speed to some degree with a controller.

 

 

 

 

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There is a formula that is used to find the correct rpm using the dia of the jar and the size of the media.

The best source for this (and lots other useful info) is Lloyd Sponenburghs book: "Ball milling theory and practice for the amateur pyrotechnician".

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There is a formula that is used to find the correct rpm using the dia of the jar and the size of the media.

The best source for this (and lots other useful info) is Lloyd Sponenburghs book: "Ball milling theory and practice for the amateur pyrotechnician".

 

Question is for a star roller. Not doing a ball mill.

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gdeputy,

 

That's correct. My formulae have nothing to do with star rolling. I've done a lot of star rolling, but that's not what's "in the book".

 

Because mixing concrete and rolling stars have a lot in common, in terms of rate-of-turn, how the materials cascade, and the 'fluidity' of the mass, most concrete mixers (of any size) turn just about the right speed for rolling stars.

 

Check out a few, and you'll see that the speeds correspond to their diameters/capacity. We purchased 'stock' small mixers from Home Depot, and modified the motor mounts for proper shielding from ignitions; we had no difficulties with rolling just about any size of star in any of them.

 

Lloyd

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Sorry gdeputy I should have elaborated, I used the same equation for both my ball mill and my star roller. I just used the desired diameter of the stars as the 'media' size when I calculated the speed for the roller.

For my mill I used 6" dia can with 3/4" media = 75 rpm

For my roller I used 9" dia and 1/4" 'media' = 58 rpm

 

Here it is in action:

Edited by Pyrodood
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Heh! That seems to work, Pyrodood. I never even TRIED to 'connect the dots' there, but you seem to have figured it out!

 

Eh... cascading is cascading. I guess the same formulas work for both activities.

 

Good job!

 

(I also like how you spun-up the speed on that slow motor. I'll bet it took some time to find the right combinations of pulleys!!!)

 

Lloyd

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ok, cool, so i'll probably shoot for a 100rpm motor that i can slow down to 50 or less and that should have me covered for a variety of sizes. Thanks!

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Thanks Lloyd,

 

I remember calling that equation "Lloyds equation" because I thought you came up with it! Anyway it is certainly useful in 'off-label' applications, no matter who the author is.

 

I don't care if someone is building a ball mill or an electron microscope they should still buy Lloyds book! :)

It has a wealth of practical information and safety tips and I still refer to it sometimes.

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