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#121 cooperman435

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Posted 20 September 2009 - 12:39 AM

option 5 is to have a driven roller with a larger/smaller diameter drive surface on one end for different mill jar sizes. it effectively slows or speeds up the surface in contact with the jar.



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Like that sort of!

#122 mike_au

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Posted 24 September 2009 - 02:13 AM

I vaguely recall someone (possiby Lloyd Sponenburgh) explaining that as you change jar size (keeping all other variables the same) two things happen:

1) the optimum RPM decreases (i.e. you want the jar to turn slower)
2) the gear ratio between the rollers and the jar changes

Either by lucky coincidence or some engineering magic, it just so happens that the change in gearing gives pretty close to the correct change in RPM as long as you are only talking about a few inches variation in jar size.

So if you optimise your mill for a 4" jar, and then chuck a 6" on (or vise versa), it won't be perfect, but it won't be too far out.

Also remember that your media diameter has some effect on optimal and critical speed. If you had different sized media for your different sized jars, you could work it so that they are both perfectly optimised running off the same roller.

Personally, I would optimise everything around the BP milling jar and just live with the fact that the other jar might not be at it's perfect speed. If the stuff in the small jar is just going to be BP ingredients then it doesn't matter if they aren't super fine before they go in to the main jar.

#123 digger

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Posted 24 September 2009 - 09:22 PM

I vaguely recall someone (possiby Lloyd Sponenburgh) explaining that as you change jar size (keeping all other variables the same) two things happen:

1) the optimum RPM decreases (i.e. you want the jar to turn slower)
2) the gear ratio between the rollers and the jar changes

Either by lucky coincidence or some engineering magic, it just so happens that the change in gearing gives pretty close to the correct change in RPM as long as you are only talking about a few inches variation in jar size.

So if you optimise your mill for a 4" jar, and then chuck a 6" on (or vise versa), it won't be perfect, but it won't be too far out.

Also remember that your media diameter has some effect on optimal and critical speed. If you had different sized media for your different sized jars, you could work it so that they are both perfectly optimised running off the same roller.

Personally, I would optimise everything around the BP milling jar and just live with the fact that the other jar might not be at it's perfect speed. If the stuff in the small jar is just going to be BP ingredients then it doesn't matter if they aren't super fine before they go in to the main jar.


OK then I have had this conversation before. It cetainly sounds sensible. However I have a variable speed drive on my mill so whenever I chuck a jar on there I tune the speed by turning it up slowly to critical speed then back it off untill the balls start crashing about (usually 0.6 to 0.7 of critical).

Anyhow I thought I should do the proof of the maths to show what the surface velocity should be for a mill jar at critical speed to see if different jar sizes do or don't have different surface velocity requirements.

So here we go:- (assume centre of mass is at the wall of the jar for simple proof)

Force on the media due to gravity: F=mg (Force (N) = m (kg) x g (m/s^2))
Centripetal force: F=mv^2/2 (v = velocity m/s)

Therefore equating the two and canceling gives the following expression for v at critical speed v=(gr)^0.5

So we can now make a table for the required surface velocity for for different mill jar sizes (given that optimum speed is 0.6 times the critical speed).

10 cm jar : Surface velocity 0.70 m/s
15 cm jar : Surface velocity 0.86 m/s
20 cm jar : Surface velocity 0.99 m/s
25 cm jar : Surface velocity 1.11 m/s
30 cm jar : Surface velocity 1.21 m/s
35 cm jar : Surface velocity 1.31 m/s
40 cm jar : Surface velocity 1.40 m/s

So it would appear that the size of the jar will effect the milling efficiency if the roller speed remains constant for different sized jars. Ok if there is a small variation in jar size 10% - 15% of diameter then it should not have a great effect as it will stay in the 0.6 to 0.7 of critical speed (given that you were somewhere towards the top end of that range) however larger variations will start to have an effect on efficiency.

So if you double the jar size you need to speed the rollers up by 40% (rpm)

Hope this helps

Edited by digger, 24 September 2009 - 09:23 PM.

Phew that was close.

#124 Guest_PyroPDC_*

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Posted 27 September 2009 - 05:22 PM

well been waiting for some time now getting all the parts together, the main problem i had was finding a belt and pulleys to fit together which i found they all have a standard code printed on then (mine was SPA), then getting a machinist to reduce the bore size of the rollers to fit the pulleys & increase the motor bore size.


the design was taken off passfire and will handle 4x 7" loaded jars. All I have left is to paint and put a cover over the motor.

never again will I go back to a rock tumbler. all I can say is from the experience with mine (what a waste of money lol)

the jar runs a 70rpm (will put a video up later)


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Edited by PyroPDC, 27 September 2009 - 06:07 PM.


#125 Vic

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Posted 27 September 2009 - 10:04 PM

Nice work PyroPDC

There is nothing worse than a crap ballmill to make you annoyed enough to make one that is the biz.
.
Some day I will post mine for you to see and you all can have a good laugh, but it works well and doubles up as a star roller as well .
Freud. Artists, in this view, are people who may avoid neurosis and perversion by sublimating their impulses in their work.

#126 cooperman435

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Posted 27 September 2009 - 10:36 PM

yeah looks very nice mate. where did the rubber rollers originate?

#127 Vic

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Posted 27 September 2009 - 11:21 PM

I would call that blatant advertising Mr Cooperman shame on you. ;)
Freud. Artists, in this view, are people who may avoid neurosis and perversion by sublimating their impulses in their work.

#128 cooperman435

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Posted 27 September 2009 - 11:33 PM

It would be excellent advertising if I got him them.

I need some new ones so am currently looking for suitable bits

#129 Guest_PyroPDC_*

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Posted 27 September 2009 - 11:35 PM

yeah looks very nice mate. where did the rubber rollers originate?


ebay m8 they were replacement A3 Printer rollers they were £6 each (including p&p)

it seems they have loads because there still selling them LINK HERE


I would call that blatant advertising Mr Cooperman shame on you. ;)


no lol but the fine quality 100x 26mm lead balls i brought off him did a great job (you should have seen the delivery man's face :P)

Edited by PyroPDC, 28 September 2009 - 12:32 AM.


#130 dr thrust

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Posted 16 September 2010 - 10:34 PM

i found this novel design for a mill thats different, what's yer thoughts ?

#131 matchkatt

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Posted 17 September 2010 - 12:00 PM

Brilliant concept! It solves the slip problem of conventional design mills, and i think that is also creates less vibration. On the other side its bigger.



#132 cooperman435

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Posted 18 September 2010 - 06:41 PM

very ingenous thinking

#133 BrightStar

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Posted 18 September 2010 - 08:35 PM

Very original, I'll give it that.

It saves the cost of another axle and a couple of bearings at the price of two big pulleys and two more belts, so probably costs marginally more.

I'd be worried that the jar would walk itself off one of the belts if the composition clumped at one end. Dropping a jar of BP from a height next to a running motor.. not great. Oh, and only one jar at a time of course.

It's probably nice and quiet though and another option to consider if you have the parts already.

#134 johnheritage

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Posted 29 September 2010 - 10:17 PM

For all HAZMAT ball milling requirement, please be speaking with us at the Legoverya processing facility for low cost solution

Is featuring variable geared drive from high torque mains power plant, slip clutching, all glass / teflon mill construction. Makes possible the handling of highly corrosive / neurotoxic chemical component. Here see processing of semiconductor for electroluminescent display

Vibration make noisy. But also make superior the mixing capabilities

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Edited by johnheritage, 29 September 2010 - 10:20 PM.


#135 digger

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Posted 29 September 2010 - 10:23 PM

:)
Phew that was close.




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