Motorized grain mill *Help*

[aeviaanah]

I'm currently designing a motorized grain mill. Ill be cloning the Monster Mill 3 Pro. 3 of 2" Diameter knurled rollers. I am curious as to if the components I have will work. This is what I have on hand.

-1/4HP Motor 1725 RPM
-30:1 Gearbox
-235in lbs output torque

Not sure if I should proceed with this equipment or not.

Still need to figure out sprockets/pulleys to get this thing to spin 100-150rpm. Currently with a 1:1 ratio the mill will turn at 58 rpm. Thinking about adding a larger sprocket off the gear box and smaller on the mill to speed it up. I don't mind not being able to crush at a fast rate (ideally 150-200??). Maybe 1:2 or 1:3 ratio?

I can adjust the roller diameter if that would help with what I have.
Less rpm would be better for such a low hp/torque motor right?

 

[YeastMode]

There are a few people on this forum that will probably have a better answer, but my first thought is that you should just get a 10:1 gear reducer and that should pretty much set you up. I know you wanted to use what's on hand but 30:1 is really slow for the application. It may work, but it may also jam constantly. I would almost just prefer a hand drill over that set up, personally.

Surplus Center has all sorts of 10:1 reducers for ~$100. A couple couplers and I think you would be all set. Adding additional sprockets intruduces additional complications, additional connections, additional open spinning objects, etc. and you may end up close to the same $100 anyway. That said, 1:3 would, I think, get you the closest. But take that with a grain of salt, because redneck engineering is only a hobby of mine. There are actual engineers on here that will probably give you an exact answer using actual math, like a wizard.

 

[Bobby_M]

1/4 horse is borderline if you want to run 100 rpm. At 53 RPM you will be ok and you need every bit of that 235 in lb.


For reference, I'm running 108 inch pounds (I think it's an 6th or 8th HP motor) on at MM2-2.0 so I also have 2" rollers but only two of them. It struggles with rye and carapils at my typical .028 gap so I either have to hand feed the hopper or run it in two stages. It also runs 63 RPM and while I wished it were a little faster due to being a shop mill, for personal use I think you'll be completely happy with 58 rpm. It will create very little dust.

 

[mbiskup]

Here is what I have as a grain mill. I have a MonsterMill 3 Pro as well.

Motor: http://www.automationdirect.com/adc/Shopping/Catalog/Motors/AC_Motors_-_General_Purpose_and_Inverter_Duty_(0.25_-_300HP)/AC_Motors-General_Purpose,_Rolled_Steel,_IronHorse_(0.33_-_2HP)/1-Phase_Motors,_56C_(0.33_-_2HP)/MTR-001-1AB18

Wormgear: http://www.automationdirect.com/adc/Shopping/Catalog/Power_Transmission_(Mechanical)/General_Purpose_Cast_Iron_Worm_Gearboxes/Dual_Shaft_Output/WG-175-010-D

The coupler is a spider coupling from Tractor Supply http://www.tractorsupply.com/tsc/search/G%26G.

Used strut channel to create a motor mount (have to use some washers as mount shims to align the coupling). And strut channel to make the cart and Kreg Casters.

Simple switch from Home Depot (DPDT or SPDT, don't recall) and SJOOW electrical cable & plug from Home Depot.

 

[aeviaanah]

Thanks for the information. A few more questions...

If I step up to a larger rpm either through the gear box or sprocket ratio- I am gaining rpm but I must be losing something, would that be torque? What are the pros and cons of using a gear box vs sprocket ratio to hit my desired rpm?

 

[mbiskup]

I am unsure about the torque and RPMs calculations, I am sure there are resources out there. If you step up to a larger sprocket, I am pretty sure you're going to need more torque on the smaller.

I chose the gearbox because I did not want pulleys sticking out of my grain mill cart, from a safety point of view and the pulley line loosing tension and having to change it out. The motor/gearbox RPMs is fixed and does not loose tension over the lifetime of the gearbox. The RPMs from the motor are known and the gearbox decreases to a fixed RPMs without doing any calculations (e.g. 10:1, 1725 motor RPM becomes 172.5 RPM)

 

[alphaomega]

Yes, you'd lose torque. At twice the speed, you'll have half the torque.
You do NOT need 100+ RPM. Slower is better (and well... slower). You just want to stay below a few hundred RPM's to minimize tearing. So the 150-250 RPM that can be seen often quoted as "optimal" is, well..., not wrong, it just doesn't state what is optimized and that would be speed, without sacrificing too much in crush quality.
Just use your 58 RPMs and allow it to take a few minutes longer.
And as Bobby_M said, you'll need the torque more than you'll need the speed.

 

[Bobby_M]

Also keep in mind that a lot of the RPMs people throw around are assuming 1-1/4 or 1-1/2" roller diameters. With 2" rollers, it pulls grain notably faster due to the linear speed of the roller surface.

The other benefit to a gearbox, besides the safety mentioned, is that sprockets and pulleys put a lot of lateral force on the drive shaft which can wear the bearings of the mill and motor down faster.

 

[aeviaanah]

I think i will go with the gear box connected straight to the mill. I may end up having a vfd I can attach to this thing.


BobbyM, thats a good point about the lateral force causing wear on the bearings.

Is there any reference as to how much torque one needs for 2" rollers? I imagine mill gap plays a big role in this? Am i on the high side or low side of that spectrum?

 

[aeviaanah]

Taking the shaft to a machinist tomorrow. This is where I am at on the design. The hopper and mill end plates will probably change.

 

[MaryB]

That motor and gear reducer are way overkill! 1/4hp and a smaller reducer would work fine. I used a 1/4hp on a gear reducer to turn a 10 foot dish antenna in 60mph winds...as you reduce speed torque multiplies...

 

[aeviaanah]

Way overkill? I thought I was on the low end of what I needed?

 

[mbiskup]

The motor runs just under 15A, can be plugged into standard outlet. Who cares if it's over powered? It was the least expensive and provided the necessary amount of power at the time of the build.

 

[Bobby_M]

That motor and gear reducer are way overkill! 1/4hp and a smaller reducer would work fine. I used a 1/4hp on a gear reducer to turn a 10 foot dish antenna in 60mph winds...as you reduce speed torque multiplies...

We're milling grain, not turning antennas.

I'll repeat, I am using this: 1/6HP @ 86RPM on a 2" two roller Monster Mill and I can stall the mill with Carapils or Rye malt. Since my previous post, I checked the faceplate and this motor runs 150 inch pounds of torque. I'm looking for a new motor that will get me over 200 in lb at 100 RPM.

 

[MaryB]

I was turning an antenna that could present 1,000 FOOT pounds or more of force to the gear reducer... it is all in the right motor and gear reducer combo. Motors that turn and elevate these 4 20' long antennas on the H frame are under 1/4 hp... the power of the wind is amazing and I have yet to stall it. In fact I could put 8 antennas on that rotor setup.

yes they are pointed at the moon! I bounce my signals off the moon as a reflector and work EU

 

[alphaomega]

Still... Wind will probably not be significant factor when sizing motor and gear ratio for a malt mill.
But you are correct in that the sizing the motor and gear ratio is the key. I'm personally building a malt mill from scratch, that will be powered by an 8W motor (or about 1/100th of a horse power). Yes, it will be slow (very slow), but it will also be small (like fit in the palm of your hand small) and cheap.

 

[Bobby_M]

The main point I'm trying to make is that the OP should not try gearing up to any faster than the current gearbox is running. The current output torque is appropriate for the load now. If geared up to 100+ rpm, it won't be any longer.

 

[aeviaanah]

Bobby I ordered a lovejoy and am keeping the current speed and torque

How long do you think it will take to get through 20lbs of grain?

 

[Bobby_M]

Roughly 13 seconds per pound so less than 5 minutes.

 

[MaryB]

Slower you mill the less the heat and heat can change the grain... I have my flour mill(for bread) setup at 60rpm. If it takes an extra 15 minutes to mill enough for 3 loaves no big deal ad it keeps the nutrients intact... I have not looked up any studies but what affect does heat from milling have on malt?

 

[alphaomega]

I don't have any data on that either, but I really don't think there is any significant heating of the malt from milling. Just touch the freshly milled malt. Does it feel hot?
Malt is crushed, flour is ground. I'd expect grinding would produce more heat from friction. But that i just my reasoning, I might be wrong.
Slower milling of malt mainly reduces the risk of tearing the hulls (leaves more hulls intact) and makes less dust. However at moderate speeds those are not big issues.
Finally, when the malt is milled what do you do with it? You mash it... And when the malt was produced, it was kilned. I can't imagine, that even if the malt were to be heated by even 10's of degrees by milling (which it isn't), it would matter at all.

 

[Bobby_M]

The only downside to slow milling is if you have a sack of malt to get through quickly. As you can imagine, running a homebrew shop, the mill gets backed up on Saturday mornings.

 

[aeviaanah]

A friend and I finally finished the Grain mill. Here are the specs

-Kegco 3 roller 11lb Hopper
-19lb Aluminum hopper extension for a 30lb capacity
-All aluminum frame
-1/4HP Motor 1725RPM
-30:1 Gearbox
-235in lbs output torque at 58RPM
-FWD/Reverse drum switch

 

[helterscelter]

that is a thing of beauty. Well done.

 

[Stealthcruiser]

Nice fabricating there!

 

[aeviaanah]

that is a thing of beauty. Well done.

Nice fabricating there!

Thanks guys. The first 3lbs went well. Time to figure out the mill gap, I bought a set of offset feeler gauges to do this.