gdeputy Posted June 6, 2017 Posted June 6, 2017 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.
Pyrodood Posted June 7, 2017 Posted June 7, 2017 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".
gdeputy Posted June 7, 2017 Author Posted June 7, 2017 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.
lloyd Posted June 7, 2017 Posted June 7, 2017 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
Pyrodood Posted June 7, 2017 Posted June 7, 2017 (edited) 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 rpmFor my roller I used 9" dia and 1/4" 'media' = 58 rpm Here it is in action: Edited June 7, 2017 by Pyrodood
lloyd Posted June 7, 2017 Posted June 7, 2017 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 1
gdeputy Posted June 7, 2017 Author Posted June 7, 2017 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!
Pyrodood Posted June 7, 2017 Posted June 7, 2017 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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