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Grain mill gearing, how many RPMs?


read 1490 times • 8 replies • posted 7/31/2012 8:45:57 PM

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t0rin0 62:1305
I just bought a 1/3 hp motor from Home Depot for $74 that has two speeds: 1140 and 1750 RPM. Iím pretty sure that both of those speeds are too fast so my question is how fast exactly do I want my grain mill to be spinning?

If it matters my batches are usually 6 or 12 gallons ranging from 6 to 25 lbs of grain. I also intend to start using some raw wheat, which from what I understand is harder to mill than malted barley.

If anyone is curious itís made for evaporative coolers (ie swamp coolers). They also have 1/2 and 3/4 hp motors that have all the same specs for about $85 and $101 respectively.

motor

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FlacoAlto 3759:17
It depends on the mill, I would contact the manufacturer as they will be able to tell you. You will definitely need to step it down, which isnít hard, use two different wheel sizes and pay attention to the circumference ratios.

My mill (a valley mill for the older homebrewers out there) is rated to go up to 300 rpm.

Raw wheat doesnít crush very well in a roller mill. In order to get great efficiencies with raw wheat berries you really need to ground it to a flower. Most homebrewers donít wory about the efficiencies and live with the poor extraction.
7/31/2012 8:55:43 PM

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t0rin0 62:1305
Just looked through the manual and if I use the lower speed setting it only runs at 1/9 hp. Is that enough? Guessing not but I dont really know.
7/31/2012 9:09:53 PM

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VsXsV 2171:44
Iíd use the higher RPM and gear it down a bit more than the lower one. 1/9 hp (whatever horse power that is ;) ) sounds to little. The gear ratio wouldnít be that much higher anyway so I donít see the point using the lower rotational speed.
8/1/2012 6:14:13 AM

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NobleSquirrel 3437:209
Originally posted by FlacoAlto
It depends on the mill, I would contact the manufacturer as they will be able to tell you. You will definitely need to step it down, which isnít hard, use two different wheel sizes and pay attention to the circumference ratios.

My mill (a valley mill for the older homebrewers out there) is rated to go up to 300 rpm.

Raw wheat doesnít crush very well in a roller mill. In order to get great efficiencies with raw wheat berries you really need to ground it to a flower. Most homebrewers donít wory about the efficiencies and live with the poor extraction.


Thatís actually why I go with flaked wheat. It achieves the same effect and is more efficient. Plus, you donít need to gelatinize the wheat.

Regarding the mill, I use a corded drill on my Barley Crusher and itís pretty painless. I will say that I tend to run it somewhat slow because I donít know how long the bearings would last if I blasted it at 300+rpms for a prolonged amount of time...
8/1/2012 7:19:34 AM

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FlacoAlto 3759:17
I meant flour above, of course

A quick calc or two:

Motor speed = 1750 rpm
Mill Speed = 300 rpm
Speed ratio = 5.83
______________________________________________
for a Motor side wheel / gear diameter = 1.5"

Solve for: Mill side wheel / gear diameter = 8.75"

______________________________________________
for a Motor side wheel / gear diameter = 2"

Solve for: Mill side wheel / gear diameter = 11.67"

You might even be able to use the same wheels & belts that are used for evaporative coolers.

I also just use a drill. I have burned through 3 drills in the past 12 years, but my mill is still going strong, despite the fact that I might exceed the 300 rpm limit by a little when I crush my grains.
8/1/2012 7:33:19 AM

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t0rin0 62:1305
After doing some more digging I found that the manufacturer recommends 150-250 rpm, so for the sake of keeping things simple Iím going with a 6:1 reduction.



Viktor, 1 hp is about 3/4 kw. So 1/3 hp is 1/4 kw and 1/9 hp is about 1/12 kw. 1/9 hp sounds pretty low to me too so Iím going with the higher speed and just going to gear it down.



Iíd be interested to hear more about the arguments for/against flaked wheat. Thatís what Iíve been using but it seems to ferment out too quick. The whole reason for the raw wheat is to give the brett some more food. The point of the mill is so that I can buy bulk grains (mostly just base malt) from a local brewery who will sell it to me at cost and $.50/lb is much better than buying it at $1.25/lb at my local homebrew store (he doesnt sell by the 50 lb bag).
8/1/2012 8:25:57 AM

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NobleSquirrel 3437:209
Originally posted by t0rin0
After doing some more digging I found that the manufacturer recommends 150-250 rpm, so for the sake of keeping things simple Iím going with a 6:1 reduction.



Viktor, 1 hp is about 3/4 kw. So 1/3 hp is 1/4 kw and 1/9 hp is about 1/12 kw. 1/9 hp sounds pretty low to me too so Iím going with the higher speed and just going to gear it down.



Iíd be interested to hear more about the arguments for/against flaked wheat. Thatís what Iíve been using but it seems to ferment out too quick. The whole reason for the raw wheat is to give the brett some more food. The point of the mill is so that I can buy bulk grains (mostly just base malt) from a local brewery who will sell it to me at cost and $.50/lb is much better than buying it at $1.25/lb at my local homebrew store (he doesnt sell by the 50 lb bag).


Why not add maltodextrin or increase mash temps? Just a thought. Also, Iím guessing that if you pulverize the wheat into flour, youíll have a better conversion efficiency as well and it will still ferment out.
8/1/2012 9:01:24 AM

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t0rin0 62:1305
Originally posted by NobleSquirrel
Why not add maltodextrin or increase mash temps? Just a thought. Also, Iím guessing that if you pulverize the wheat into flour, youíll have a better conversion efficiency as well and it will still ferment out.


I have increased mash temps to 155, do I need to go higher? Never used maltodextrin, how much are we looking at? Iíll try a batch with cracked wheat this weekend and see what does to my efficiency.
8/1/2012 9:10:21 AM

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