Is there a minimum Grain mill speed?

[mattd2]

So just finished getting my DIY mill up and running and the next hurdle is motorising it. As is normal over here in NZ stuff cost $$$ (well it seems that it cost more than it would if I lived in the USA ) so I am looking at my options for grain mill motors, I am keen for a direct drive geared motor so reduce spinning parts in the house (young kids).
I have found some that will do that arn't hugely expensive and going of someones post that 16 #-in is the lowest you would want to go (needs the mill running before grains added). And most say you want around 200 rpm.
But the speed is right down <100 rpm, possibly even 50 rpm .
My rollers are 2" and I don't care how long it takes to crush a batch worth of grain (as long as I don't have to be watching it the whole time).
So my question is, is there a lower limit on the speed you want to run the mill at? i.e. am I going to have issues with grain not being drawn into the mill, etc. if I run it too slow?

 

[jpalarchio]

I have a JSP mill and use this motor: http://www.surpluscenter.com/item.asp?item=5-1074

It's about 100 rpm which I find sufficient and I'm generally milling about 30 lbs of grain. It's 30 in lbs of torque and I can't image going much less than that. I'd guess that 16 in lbs wouldn't be enough but perhaps someone who has tried can help you there.

 

[microbusbrewery]

So just finished getting my DIY mill up and running and the next hurdle is motorising it. As is normal over here in NZ stuff cost $$$ (well it seems that it cost more than it would if I lived in the USA ) so I am looking at my options for grain mill motors, I am keen for a direct drive geared motor so reduce spinning parts in the house (young kids).
I have found some that will do that arn't hugely expensive and going of someones post that 16 #-in is the lowest you would want to go (needs the mill running before grains added). And most say you want around 200 rpm.
But the speed is right down <100 rpm, possibly even 50 rpm .
My rollers are 2" and I don't care how long it takes to crush a batch worth of grain (as long as I don't have to be watching it the whole time).
So my question is, is there a lower limit on the speed you want to run the mill at? i.e. am I going to have issues with grain not being drawn into the mill, etc. if I run it too slow?

50 RPM seems awfully slow...that's less than one revolution per second (5/6ths to be precise). Seems like it would have a hard time pulling grain through at that speed. If it did work, it might mean you'd have to start milling the night before brew day.

 

[mattd2]

I have a JSP mill and use this motor: http://www.surpluscenter.com/item.asp?item=5-1074

It's about 100 rpm which I find sufficient and I'm generally milling about 30 lbs of grain. It's 30 in lbs of torque and I can't image going much less than that. I'd guess that 16 in lbs wouldn't be enough but perhaps someone who has tried can help you there.

Yeah they said 16 in lbs was the very very very lower limit, i.e. you can struggle through at this but don't expect it not to jam.
i was working on needing twice this - so your 30 in lbs sounds like I was about right in my assumption
the one I have found is 160 rpm, but they state it has ~50 in lbs @ 55 rpm.

 

[mattd2]

50 RPM seems awfully slow...that's less than one revolution per second (5/6ths to be precise). Seems like it would have a hard time pulling grain through at that speed. If it did work, it might mean you'd have to start milling the night before brew day.

With the 600 rpm drill on it last night I went through 1 kg of grain in less than 10 seconds (much less but I'll go with 10 seconds). at 50 rpm, assuming no issues with grain going into the mill, it would take 12 times as long so thats 120 seconds or 2 minute/kg. So for a normal 10 gallon batch with 10 kgs of malt that would be 20 minutes. I would be happy with this if (and really only if) I could turn it on and walk away, come back 20 minutes later and the job was done
The motor I found was 160 rpm (as mentioned above) but only had the torque rating at 55 rpm