# I made a mill



## Matplat (2/5/16)

Wassup peeps... check it out, I made a mill! #stoked

I made the rollers from 6"NB pipe which works out to 139mm OD in real money, and they are 150mm wide.

The motor i was given to me and its 0.37Kw 2800rpm, it turns a 1 1/2" pulley stepped up to a 14" pulley which means the rollers should be doing 300ish rpm.

I got a mate to knurl the drive roller (I left the slave roller smooth), and I told him to do it quite light as the rollers are bigger than most homebrew mills. Originally i wasnt going to knurl them at all... when I saw what he did, I thought it was too fine and would get caked up and stop drawing the grain through, but it seems fine so far.

I set it first at 1mm gap, but it seemed like it ripped the husks too fine, so I knocked it back to 1.3mm which seems alot better, opinions appreciated. I will post the 1.3mm photo in the next post so you know which is which.


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## Matplat (2/5/16)

1.3mm gap crush sample. 

Oh yeah, I dunno if it makes much difference, but both these test samples were done using some spec malt rather than base malt.


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## blotto (2/5/16)

Seems to me like your still doing a bit of damage. I wonder if having such a large heavy idle roller is causing a lot of tearing. I have heard of people putting an o ring on one or both of the rollers to get the second one turning. If you give that a go it might then pull your grain through nice and gentle .

Edit: fantastic job though!


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## Maheel (2/5/16)

is it just "pipe" and you made centers and got them nicely centered?
if yes how did you center it for the ends etc?
what sort of "pipe" is it etc.

eg weld on the end rods onto flat plate and lathe it for the pipe or something ?


i have a workshop full of the right tooling but have never seen any "free" solid rod big enough to play with....


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## MickGC (2/5/16)

Looks awesome mate!
one thought, having rollers with such a large diameter, you may need to slow them down a fair bit,
i have a kegking 2 roller, and it is recomended to run at 180 RPM,
with rollers approx 30mm [email protected] rpm it gives a surface speed of 28cm/Sec
with your 139 Dia [email protected] you have a surface speed of 219cm/Sec

could be worth a shot if you can find a way to try running a slower speed, might not rip the grain so much
The calculator i used says 39 rpm would give a surface speed of 28cm/Sec

http://www.onlineconversion.com/wheel_surface_speed.htm
this was the calculator i used for surface speed.

I could also be completely wrong and it not work at all


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## Matplat (2/5/16)

Yeah its just 6"NB medium wall pipe, so wall thickness was approx 4-5mm. I used 1"round bar for the axle, then cut appropriately sized discs to fit inside the ends of the pipe. 

Weld the discs to the shaft, turn down the outside so its centered, slide the pipe over the discs, weld the pipe in place then turn the outside down until its all concentric.


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## Benn (2/5/16)

Nice job Matplat,


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## Matplat (2/5/16)

Yeah, I wondered if it might be going a bit quick... I will give a brew a go, keep some rice hulls on hand and see how the efficiency fairs!


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## Benn (2/5/16)

Keep us posted mate, I'm in the process of building a mill too. Rollers are 150mm cast iron industrial bearing things for moving steel beams around factory floors or something. Apparently they're just about un-knurlable but a steel guy is putting them in a machine that will cut an even spacing of fine 'V' grooves around the circumference.


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## Danscraftbeer (2/5/16)

Wow. Too many questions to ask.
This gives me a feeling that my standard cordless drill mill will inevitably fail me someday and I will look back on this. B)


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## Weizguy (2/5/16)

Nice engineering!

I thought that the grist pictured above was a bit torn up, and believe the 300 rpm will do that. I have 60 mm rollers and find that hand-cranking at about 100 rpm (approx) does it right, with lots of cracked grain that break apart when touched, and little husk tearing.
You got some big rollers and a lot of surface speed. Some research is in order to maximise your milling. I think you may need to slow it down quite a bit to get the best efficiency.

Was also thinking it's fine if you Brew in a Bag, but then again I don't, so I cant't be certain.

Your project has begun. Good luck with fine tuning.


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## Weizguy (2/5/16)

Benn said:


> Keep us posted mate, I'm in the process of building a mill too. Rollers are 150mm cast iron industrial bearing things for moving steel beams around factory floors or something. Apparently they're just about un-knurlable but a steel guy is putting them in a machine that will cut an even spacing of fine 'V' grooves around the circumference.


IIRC, larger rollers fare better without a knurl, as they can grip and pull the grains through easier due to the angle between the rollers. I've been reading a lot about grain mills recently, in order to work out if I need to motorise my mill.

I think I can cope with hand-cranking a few more years until the arms get weak. I'm really happy with around 90% efficiency (combination of milling and sparge technique). Testify!


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## rude (2/5/16)

I made one years ago & power it with a windscreen wiper motor
Not sure of the speed but pretty slow

Might be an option for you to try

Forget my gap but its large 1.4mm ? 50mm rollers


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## Benn (2/5/16)

How's the windscreen wiper motor go for torque? I would have thought it would burn out. I'd considered using one but found a big 240v thinking a ww motor wouldn't handle the load.


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## Weizguy (2/5/16)

Forgive me for butting in again, but DC motors provide far more torque than AC. Maybe read through 33 pages of the Mill Motors thread to get more info.

http://aussiehomebrewer.com/topic/44766-mill-motors/ (* edited to add the link)


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## Benn (2/5/16)

There's a 33 page mill motor thread?!!
..I'm chuckin a sickie tomorrow!

The compactness of a ww motor would be ideal, and there's not a massive belt n pulley for me to tangled in,


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## Matplat (3/5/16)

Damn... guess I should have given it a go without knurling first. Lesson learned for you Benn... If the grain husks are damaged too much, is there a risk of tannin extraction? Or more just a stuck mash?

I brew on a 1v recirc, bigW malt pipe... 

Considering I got the motor free, I could afford to get a new one at 1400rpm and use the current gearing. As I understand it, you can't slow down AC motors with a speed controller as the current draw goes up and it overheats.

Otherwise i might need a lay shaft to step the gearing down again... but that's getting a bit bloody complicated and expensive.

I will try opening the gap a fraction more to see how it goes.


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## Benn (3/5/16)

You could change your pulley sizes to slow the roller speed, from what I've heard it's best to run with a small pulley on the motor so it's not working too hard but it all depends on the load I guess. Maybe you could get away with a slightly larger pulley at the motor end if your still getting a dodgy crush after gap adjustments are made.


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## Matplat (3/5/16)

Yeah I would need a smaller pulley than what I already have on the motor... at the moment it is 1 1/2" on the motor and 14" on the roller I think 1 1/4" is the smallest you can get, which gets me down to 250rpm... but I think I may do that as well as halve the motor speed...


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## Topher (3/5/16)

Good work. Mad skills! You made an entire mill! 

Compared to me who spent 30mins swearing while cutting a hole in a bucket to make a hopper.


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## n87 (3/5/16)

.


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## Matplat (3/5/16)

Matplat said:


> As I understand it, you can't slow down AC motors with a speed controller as the current draw goes up and it overheats.


Is there anyone here that can confirm or reject my claim above?


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## Ducatiboy stu (3/5/16)

Matplat said:


> Yeah I would need a smaller pulley than what I already have on the motor... at the moment it is 1 1/2" on the motor and 14" on the roller I think 1 1/4" is the smallest you can get, which gets me down to 250rpm... but I think I may do that as well as halve the motor speed...


You probably want to get it to around 150rpm on the roller. remembering that larger rollers will have a faster surface speed compared to smaller rollers at the same rpm


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## Mardoo (3/5/16)

Matplat said:


> Is there anyone here that can confirm or reject my claim above?


I can't, but variable speed electric drills come to mind. Are those DC motors with a transformer?


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## Dave70 (5/5/16)

Matplat said:


> Is there anyone here that can confirm or reject my claim above?


This was possible with about every power drill I've ever owned. You varied the chuck speed according to how far you depressed the trigger. 
Some even had dials that would govern how fast the motor spun. I actually have a 5" grinder (GMC, 4 years of abuse and counting?!.) with the same feature. 
So based on purely anecdotal, sample size of one observation, yes it's possible. Probably not optimal however. Pretty sure most stationary electric motors would be manufactured to run at a certain RPM and current for a reason.


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## Matplat (5/5/16)

Yeah, I'm going to flog the motor from a small drill press.

Drill presses seem to go cheaper second hand than the motors that run them.... pool pumps can be had for even less, but they all seem to have the 2800rpm motors that I am already using.


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## wide eyed and legless (5/5/16)

Have a look on eBay. (speed controller)


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## TheWiggman (5/5/16)

Most large AC motors run based on line frequency and number of poles. Here's a reference as an example - http://www.engineeringtoolbox.com/synchronous-motor-frequency-speed-d_649.html
If it's an induction motor, your motor will have the number of poles written on it as well as run speed. To vary the speed you either need to change the number of poles (i.e. buy a new motor) or alter the line frequency using a VVVF drive or similar. If you have a brushed universal motor on the other hand the speed can be controlled much the same as an electric drill using the appropriate controller.

Agree with the above posters, with rollers at that diameter and speed it would be absolutely rip-tearing through that malt with reckless abandon. Large diameter rolls is a good thing but you really need to slow it down. Look into a lower speed motor or controller if you can. Otherwise, add an extra shaft for the pulleys for an extra reduction. And a cage to ensure fingers remain on the ends of you palms.


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## Matplat (19/6/16)

Afternoon all, so i got a motor from a drill press second hand which has cut the speed in half so theoretically I should now be running at 150rpm, but I don't have a strobe to confirm this... anyway here is 100g of grain that I put through it at 1.5mm gap, I think it looks pretty good but could possibly close the gap a bit. The proof will be in the brewing, but I've got to make a hopper first


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## mash head (20/6/16)

Looking good, you can get a cheap rev counter off ebay with a magnet pickup if you need. I put one on my harvester thrasher when the original cable drive rev counter was going to cost heaps to replace. Make sure you are not getting any whole grains getting through as the grain size on some malts can vary a lot.


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## Matplat (21/6/16)

Yeah good idea but I don't think I'm that bothered about knowing the exact rpm, as long as I can get good efficiency... 

I was thinking about doing a few mini-mashes on the stove to evaluate efficiency at different gap settings, however that would be BIAB whereas my brew system is 1v malt pipe. Is the main consequence of milling too fine getting a stuck mash? I'm sure tannin extraction would also become an issue at some point also, but would you run into a stuck mash first?


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## wynnum1 (21/6/16)

Getting a stuck mash would be ok if doing tests to evaluate need to test until it fails.


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## dannymars (21/6/16)

I found that the bigW malt pipe is fairly prone to stuck mashes, mine is anyway.


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## Matplat (21/6/16)

Cut some more holes dude, last brew my LBP couldn't barely keep up with the flow through the grain bed...


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## Matplat (18/7/16)

So just did the first brew last night with the gap set at 1.4mm with rollers at calculated 150rpm. I did an American wheat 50:50 pale and wheat. 5kg of grain crushed in 2-3 mins max, and I hit 75% eff so I'm stoked.


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## Benn (18/7/16)

Good work Matplat :beer:


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## Ben1 (22/7/16)

Out of curiosity, what was your eff before matplat?


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## Matplat (23/7/16)

Last few brews were 70, 65, 58 in chronological order, but has been as high as 80. I set my recipes at 70, consistency is my main problem, however the beer still tastes good!

Achieving 75 this time round wasn't necessarily a step up, simply that I was expecting less while fine tuning the mill.


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## Hpal (23/7/16)

rude said:


> I made one years ago & power it with a windscreen wiper motor
> Not sure of the speed but pretty slow
> 
> Might be an option for you to try
> ...


Here's mine http://cdn.aussiehomebrewer.com/uploads/albums/gallery/album_1215/gallery_26644_1215_249415.jpg
Powered with a wiper motor, slow but steady, 65mm rollers and I've set gap at 1.6mm, any smaller is too fine.
Good work on the mill mate, looks great! http://cdn.aussiehomebrewer.com/uploads/albums/gallery/album_1215/gallery_26644_1215_658805.jpg


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## Matplat (23/7/16)

Wow, 1.6mm! I think that the optimum gap size depends alot on the size of the knurl on the rollers. Looks like off-the-shelf mills have a much coarser knurl. If I were to set the gap at 1mm as it seems alot of people do, I would end up with flour.


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## Ben1 (23/7/16)

Out of curiosity, what was your eff before matplat?


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## Weizguy (23/7/16)

Matplat said:


> Wow, 1.6mm! I think that the optimum gap size depends alot on the size of the knurl on the rollers. Looks like off-the-shelf mills have a much coarser knurl. If I were to set the gap at 1mm as it seems alot of people do, I would end up with flour.


Mostly agree. The optimum gap size depends on both the knurl size and, more importantly, the roller diameter - which determines surface speed.

It's great that you have 75% efficiency. I'd be happy if I had that as a consistent result.


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## Ducatiboy stu (23/7/16)

My 50mm rollers need about 0.9mm and they have a fairly decent knurl.

I also dampen the grain first which aslo make a fifference

I try to aim for about 20-30 % flour


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## Lyrebird_Cycles (23/7/16)

Matplat said:


> As I understand it, you can't slow down AC motors with a speed controller as the current draw goes up and it overheats.





Matplat said:


> Is there anyone here that can confirm or reject my claim above?


A bit belated but here goes:

Power = torque x speed, so for any motor if you reduce speed at constant power you must increase torque. For most motors increasing torque increases current draw BUT in this case the torque requirement should go down with the speed so that doesn't apply.

Next we have the problem of back EMF: any motor also acts as a generator, producing a voltage opposing the drive voltage, called back EMF. Forward voltage is the difference between drive voltage and back EMF so when the motor speed is reduced the forward voltage is increased. If the winding impedance was constant, this would increase current draw BUT winding impedance on a single phase motor is a complex function of load and speed, as below:







The next problem is that the cooling fan is attached to the motor shaft so as the motor slows the cooling is reduced. Some motors have a special cooling fan drive to offset this but yours is not one.

All this is moot if you use a VFD, every one I've seen has a facility to control the drive voltage and current as required.

BTW I don't think the speed is you actual problem, I think it's the combination of knurling and undriven second roller. Real malt mills run quite fast, up to 4 m.s-1at the surface (about 500 RPM for a 150mm roller, though rollers are usually larger than that).

The problem with the undriven roller is obvious when you ask yourself: what's making it move? The answer is the drive force is being transmitted through the grain. Since you've got drive force on one side and resistance on the other, this places the grain in shear. Shearing grain tears the husk.


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## Matplat (2/11/16)

Been meaning to update this thread for a while....

I took lyrebird's advice and made some effort to drive the slave roller, I got a few decent wide rubber bands and wrapped them around the drive roller.

It made adjusting the gap a little harder, but it worked! I wasn't sure that it would, because the feeble grip exerted by the rubber band contact patch on the dusty slave roller, didn't seem like it would make much difference...

The immediate difference I noticed was when mashing in, almost zero dough balling compared to before, and, subsequently, the flow through the bed was much better during the mash. I also gained a few efficiency points in the process.

I think I will transfer some of the rubber bands to the slave roller, so it will then be rubber driving rubber, rather than rubber driving metal.

But yeah, anyone looking for a cheap/simple way to drive a slave roller, this is a totally viable option.


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