Jim Tabor on wed 25 jul 01
Anyone with a simple ball mill design? Motor size, pulley sizes, rollers
and bearings?
I didn't find anything related in the archives.
Ababi on thu 26 jul 01
Go to http://www.bath.ac.uk/~ccsjrh/pottery/ballmill.htm
Ababi (make one for me too)
 Original Message 
>Anyone with a simple ball mill design? Motor size, pulley sizes,
rollers
>and bearings?
>I didn't find anything related in the archives.
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Fredrick Paget on sun 29 jul 01
Valerie 
I am afraid it would not work. The reason is that it would be far too slow
and the balls would just roll around inside the jar on its inside surface.
That would have very little effect.
The way a ball mill (also known as a jar mill) works is to have the balls
cascade down from the top of the jar in a sort of waterfall of balls. You
get this by running it in the critical speed range so the balls go around
on the surface of the jar until they get to the top of the jar and then
fall in a cascade. It is a sort of balancing act between centrifical force
and gravity. If you run too slow the balls stay at the bottom and just roll
along and gravity wins. If you run too fast the balls cling to the inside
of the jar and go around without rolling. they stay up and do not fall from
the top  centrifical force wins.
The critical speed in RPM is easy to calculate:
It is 54.19 divided by the square root of the internal radius of the jar
measured in feet.
This gives the critical speed. THe mill is operated at from 64% to 67% of
the critical speed for best effect.
Speaking of clothes dryers I made my ball mill in part from salvage from a
defunct clothes dryer. The electric motor was still good and I used that.
It runs at 1750 RPM. I cut up the case of the dryer to get sheet metal to
make the belt guard and one of the roller wheels that the dryer drum ran on
was used as an end roller to keep the jar in position. The rubber rollers
that the jar rests on came from an old roller skate. the kind with four
wheels, not the newer inline skate.
I bought the biggest pully and the smallest pully the hardware store had
for a 1/2 inch V pelt. The big one (about 12 inches) is at the top and runs
a shaft that has 2 skate wheels on it that are firmly attached on the shaft
so that they turn with it .The small one (about 1 1/2 inch) is on the motor
underneath. Another shaft has two skate wheels on it that are free spinning
on their own ball bearings. The jar rests between these two shafts so it is
supported and driven. I can run either a 1 quart or a 1 gallon jar and they
are both within the critical speed range.
The frame is welded up from square tubing and welded on tabs support the
fixed shaft and motor mount. The driven shaft runs in two pillow block
bearings from the hardware store. The shafting and spacers are sold there
too. The motor mount underneath is adjustable up and down to tension the
belt correctly.
I realize that this is not a real easy thing to build and you would really
need to know welding and machinist skills to get it together.
If you make one in Europe the electricity is 50 hertz instead of the 60 we
have here in the USA so your junk motors will probably be 1450 or possibly
2900 RPM. You will have to figure out the reduction ratio from the formula.
Fred Paget
>I've been looking for the same thing. Actually, I've been thinking about
>using the clothes dryer in the "cool" position and ducttaping containers of
>glaze to the ribs on the inside; has anyone done this? I will probably
>double contain the glaze (jar inside a plastic container).
>Valerie Johnson
>Eads, Tn
In cold and foggy Mill Valley, California, where this summer is the coldest
winter we have had in a long time.
Valerie Johnson on sun 29 jul 01
I've been looking for the same thing. Actually, I've been thinking about
using the clothes dryer in the "cool" position and ducttaping containers of
glaze to the ribs on the inside; has anyone done this? I will probably
double contain the glaze (jar inside a plastic container).
Valerie Johnson
Eads, Tn
Fredrick Paget on mon 30 jul 01
There is an error in my last post It should be >=88This gives the
critical speed. THe mill is operated at from 64% to 87% of the critical
speed for best effect. =88
>The critical speed in RPM is easy to calculate:
>It is 54.19 divided by the square root of the internal radius of the jar
>measured in feet.
>This gives the critical speed. THe mill is operated at from 64% to 67% of
>the critical speed for best effect.
=46red
=46rom Fred Paget, Marin County, California, USA
Michael Mandaville on fri 12 oct 01
On Mon, 30 Jul 2001 11:05:44 0700, Fredrick Paget
wrote:
> There is an error in my last post It should be >=88This gives the
>critical speed. THe mill is operated at from 64% to 87% of the critical
>speed for best effect. =88
>
>>The critical speed in RPM is easy to calculate:
>>It is 54.19 divided by the square root of the internal radius of the jar
>>measured in feet.
>>This gives the critical speed. THe mill is operated at from 64% to 67% of
>>the critical speed for best effect.
>Fred
>
>From Fred Paget, Marin County, California, USA
Hello, Fred.
Thank you for posting this valuable information. I am now using it to
design a ball mill which will be powered by the drive wheels of my self
propelled mower!
Regards,
Michael Mandaville
Austin, Texas
 
