Motor size (HP) for grain mill?

What size motor would you guys recommend for motorizing a grain mill?

I plan on a 110V TEFC motor, but I was unsure on HP rating. . .I know more is better, but I didn't want to go overboard.

I plan on milling 50 lb. bags of grain at a time. . .the rollers are gonna be 1.5"-2" solid stainless steel 10.5" long (10.5" is the actual length of the portion doing the milling. . .the OAL of the roller will be longer due to the support shaft on one side and the drive shaft on the input side) and I plan on driving both rollers through a set of gears.

Thanks!

At least 60+ in-Lb torque at whatever your speed, but 175 RPM is a sweet spot.

Mine is a 1725 RPM 1/3 HP that gives me 100 in-Lb torque at 172 RPM with aid of a 10:1 ratio gearbox (reducer). This is an easy motor to find on ebay.

So, I'd not go any less than 1/4 HP, to directly answer your question.

Would 3/4 HP be overkill?

I'm planning on milling grain a 50 lb. bag at a time.

Thanks. . .also I saw that the MaltMill was set to run at 400 RPM when motorized (3.3 seconds for 1 lb. of grain); is the 175 better? Any other suggestions?

I.e. are smooth rollers more desirable than knurled rollers? Spacing between rollers (I saw the Malt Mill was set for 0.045" between the rollers)?

Thanks!

It only draws the torque it needs.

Knurled rollers are needed on smaller diameter bars to grab the grains. A large diameter smooth roller is more ideal.

I'd have to look on the gap. I think that is pretty standard as shipped on mills. Most tighten it up from there.

I was planning on 1.5" rollers 10.5" long out of SS. . .I was going to try smooth rollers initially just because knurling is one extra step in the machining process that if unecessary I would prefer not to do, plus it's quite a bit of effort to get all the little metal shavings out of the knurls after machining to make sure there are none left to make there way into the crushed grain.

I was planning on both rollers being driven rollers (1.25:1 gear ratio between the gears) as well instead of a driven roller and an idler roller.

Considering the issues many report with 1.5" diameter knurled rollers, I suspect 1.5" diameter rollers are too thin to go smooth. The only attempts at smooth rollers I've seen in the forums were much bigger - like 4" diameter or larger.

Curious about that gearing between the rollers. Are you saying one roller will spin faster than the other?

Cheers!

I second that 1.5 is likely too small for smooth.

I prefer the idle roller over 2 driven. If a rock or similar is in the grain then it has a lot better chance of not being forced through. With 3/4 you might do some damage.

Yuri-rage built a mill. Have you found his thread? Might help you avoid some of his pitfalls. One was too small of motor for his rollers if I remember. You should be covered there.

Bits of ss in the grist shouldn't be a problem. Just clean off any machining oil.

Thanks for the tips guys. . .I don't spend much time on this forum so I haven't seen Yuri-Rage's mill thread, but I will look for it tonight, thanks for pointing me in that direction.

Is this the thread you are referring to?

https://www.homebrewtalk.com/f51/diy-ish-cnc-mini-mill-210443/

I also found a thread on roller diameter effect, but I haven't read it yet. . .will be reading it tonight.

Thanks again!

OK. . .I should have checked that thread first, that was not the grain mill thread, that was an actual CNC mill. . .

. . .but I think I found it this time; I'm starting it now. . .

https://www.homebrewtalk.com/f11/diy-grain-mill-12858/

The roller diameter issue makes sense to me; I will have to modify my CTC mounting distance and size of gears, but that's no big deal since I haven't actually started making any parts yet (guess it's a good thing I was busy today because I intended to start making parts if I had time).

ebay has a good looking 1/2hp motor going for $19 + $9 for shipping. Item number 180821254709. Here's the link (16 feb 2012, it'll expire in a week or so)
http://www.ebay.com/itm/1-2-HP-110-...709?pt=LH_DefaultDomain_0&hash=item2a19c96235

Thanks for the link to that motor. . .

. . .Yuri's grain mill thread was pretty good; I will start a thread on mine (the mill actually won't be mine though. . .it's for some friends) once I finalize the design.

I will be going for rollers ~2" in diameter.

atomicjoe23 said:

I was planning on 1.5" rollers 10.5" long out of SS. . .I was going to try smooth rollers initially just because knurling is one extra step in the machining process that if unecessary I would prefer not to do, plus it's quite a bit of effort to get all the little metal shavings out of the knurls after machining to make sure there are none left to make there way into the crushed grain.

I was planning on both rollers being driven rollers (1.25:1 gear ratio between the gears) as well instead of a driven roller and an idler roller.

Click to expand...

Knurling the rollers shouldn't create any metal chips, as most methods of knurling simply upset the material, not remove any. Every time you use a mill there is some small erosion of the surface of the rollers to get into the grain, but even larger chips would stay in the grain bed and not make it into the boil kettle.

It seems to me that having the rollers run at different speed would result in more shredding of the husks instead of simply crushing them. I'd do quite a bit more research before making both rollers driven.

The theoretical and the actual are two different things though. . .the knurling rollers displace the metal, but as the metal is displaced it is squished up so that the sharp edges of the knurlers will cut little bits of metal that are very small and stay in the knurl for quite a while, even running the parts through the solvent washer takes a couple of times through to get rid of it all. . .you can tell when you run your hands over or use a freshly knurled piece. . .the other way metal chips get in the knurl is that you normally take a very light skim pass after you finish knurling so that the part is uniform in diameter and the knurls aren't so sharp as to cut you/be painful in use.

The idea to have both rollers driven came from the JSP Malt Mill which has two driven rollers. . .if it were to turn out to be a bad idea it's as simple as removing one gear, taking all of 30 seconds. . .much less work than trying to add a gear later on down the road, but I will look into it further.

Thanks for the tips and keep them coming!

Before you buy a motor, check the local scrap yard first. I got mine for < $3. It's a 1/4 horse, 1725 RPM. With my sheaves, it runs at just under 300 RPM.

I've got 2 fractional HP motors sitting in my garage which I would use if this were for me, but it's for a local brewer so they are gonna get a new motor. . .no scrap yard motors for a paying customer unless they wanna buy their own scrap yard motor, but thanks for the tip.

ChuckO said:

It seems to me that having the rollers run at different speed would result in more shredding of the husks instead of simply crushing them. I'd do quite a bit more research before making both rollers driven.

Click to expand...

I could see the husks getting shredded with knurled rollers, but is that something you would really need to worry about with smooth rollers. . .they should just crush the grain/crack the husks between the rollers if they are smooth wouldn't they?

atomicjoe23 said:

I've got 2 fractional HP motors sitting in my garage which I would use if this were for me, but it's for a local brewer so they are gonna get a new motor. . .no scrap yard motors for a paying customer unless they wanna buy their own scrap yard motor, but thanks for the tip.

Click to expand...

Gotcha.

What is the goal in having the rollers run at different speeds?

SankePankey said:

At least 60+ in-Lb torque at whatever your speed, but 175 RPM is a sweet spot.

Mine is a 1725 RPM 1/3 HP that gives me 100 in-Lb torque at 172 RPM with aid of a 10:1 ratio gearbox (reducer). This is an easy motor to find on ebay.

So, I'd not go any less than 1/4 HP, to directly answer your question.

Click to expand...

I'm currently using a 1725 RPM 1/2HP motor with a pulley system. I've had enough of the pulley system (can never seem to get the belt to stay tight enough to grip well, so I end up having to pour the grains slowly into the hopper).

Would this gearbox reducer work? I've got a 1/2" shaft on the motor, and a 1/2" shaft on the Monster Mill. I'm not sure what I would need in terms of couplings to get it all to hook up.

http://www.surpluscenter.com/item.asp?item=13-133-10-R&catname=powerTrans

I have a question. You say that you will mill 50lb at a time. Will you be using that amount in less than 2 weeks?

Milled grain goes stale/loses it's freshness much faster than whole grain. I mill only what I need for the day's brew. I also mill it no earlier that the night before brew day.

RDWHAHB said:

What is the goal in having the rollers run at different speeds?

Click to expand...

I'm not sure what the goal is for the MM, but the reason I have them running at different speeds is to accomodate the the spacing between the rollers and still have the gears correctly mate with each other.

The JSP MM is set for a 1.25:1 ratio. . .what I'm currently working on will have 2" plus diameter rollers and a 1.33:1 ratio (using an 18T and 24T 16P spur gears).

kh54s10 said:

I have a question. You say that you will mill 50lb at a time. Will you be using that amount in less than 2 weeks?

Milled grain goes stale/loses it's freshness much faster than whole grain. I mill only what I need for the day's brew. I also mill it no earlier that the night before brew day.

Click to expand...

The guys that will be using this will be using that much and more in a single day. . .so no problem with it losing it's freshness. They are the smallest operating brewery in WA state and right now they are making do with a small 3/8" hand-held cordless drill run mill with 5" long 1.25" diameter rollers!

I haven't personally started brewing all-grain yet which is why I'm trying to get as much input from those that do. . .I'm a Toolmaker by trade so designing and making the mill isn't a problem, but I want to make sure it will be as good as I can possibly make it for them the first time around so I wanted to get as much input as possible.

So thanks so far for all the help!

@RMullins. . .yes that would work, ideally I would use a reduction coupling similar to that as well, but since I'm doing this out of my pocket for them I'm not going that route. . .yet.

Well if the gear ratio works for the maltmill then it ought to be ok. Plently of happy customers use those.

Is this going to be an adjustable gap? If so, how is the gear lash going to be maintained? I'd much rather have an adjustable gap and and idle roller than gear driven without gap adjustment.

Yes it will be adjustable and gear driven. . .spur gears don't fully bottom out when they mate with each other (at least they aren't supposed to. . .there is one that does, but I'm not using that type of spur gear). . .so the gap won't be the exact gap that you calculate, but it will be fine. . .

. . .talking with the brewers they want to be able to adjust the gap between 0.040 and 0.049" so 0.009" is nothing to worry about, that's about the thickness of between 2 and 3 sheets of notebook paper.

Hows the project coming?

Tried out the smaller knurls on the replacement rollers I made for their Barley Crusher and the little knurls didn't work. . .so I'm making a cut knurling tool to be able to cut the deep aggressive knurls in the rollers.

After I get the tool made (will probably take me a month at least since I'm doing this on the side) I will be able to start working on the 10.5" long x ~2.25" diameter grain mill.

Did you consider getting a 2.25" dia x 12" length roller from mcmaster carr and just machining the axle ends? They have 1018 steel, hardened steel and stainless steel. Some variations on diameter and lengths depending upon material. That would leave just building an endplate with some type of adjustment. And the knurling option.

No I had not. . .buy thanks for the tip, that could save quite a bit of time. . .greatly appreciated!