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Old 10-01-2007, 02:48 PM   #1
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Default Grain mill roller diameter?

In a few months I will be moving back to the farm where I will have access to all kinds of fun toys (lathe, mill, welder, etc.). I think a grain mill will be my first major project.

My question is about roller size. From what I can tell most homebrew mills have about 2” diameter rollers. But, I think I remember reading an article about how professionals breweries use large diameter rollers (maybe about 6”). If my memory is correct the larger diameter means they don’t need a knurled surface to pull the grain through the mill. Anyone know anything about professional milling? Is my memory correct about a larger roller diameter? Is it a better crush (better efficiency) if the rollers are smooth rather than knurled?

FYI, this is a design I am considering:
http://suburb.semo.net/jthornton/Mill.htm

Thanks in advance.

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Old 10-01-2007, 03:12 PM   #2
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my mill was made for me by a machinest buddy, it has 2" rollers (knurled) and works like a charm.
I'm pretty sure you're correct that large rollers would necessarily need knurling but I chose smaller diameter to save cost. 6" bar stock would be pretty costly I think

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Old 10-01-2007, 04:04 PM   #3
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The larger the roller, the less steep the entry angle is so the roller grips the grain more gradually. It doesn't need the knurl bite. 2" works just fine though.

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Old 10-02-2007, 03:56 AM   #4
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Couple questions for the group
Anyone have any formula's for calculating the horsepower/torque requirements for various sized roll diameters/lengths.
Has anyone considered making rollers out of pipe or tubing to save on the cost of large diameter bar stock, as in making the end disks from Carbon steel plate stock and roll covers from SS pipe.

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Old 10-02-2007, 01:20 PM   #5
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No sure about torque, but check out the link in my orginal post for info on a mill made from pipe.
http://suburb.semo.net/jthornton/Mill.htm

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Old 12-15-2009, 06:38 PM   #6
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curently iam working on 4.5" smoth oak rollers, i run some tests and i think it will work like a charm after i add a sprockets and a chain drive. its under DIY "woody 3.0xpr".

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Old 12-16-2009, 02:06 AM   #7
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The book "Brewing - Science and Practice" from the CRC Press has almost a whole chapter on Milling. In part, it says:

Roll (or roller) mills are commonly used in breweries. The rollers work in pairs. The malt grains are delivered to the first pair of rolls by a feed roll that determines the feed rate and is intended to deliver each corn `end-on' to the working rolls. Each corn is drawn between the rolls and is crushed, sheared (if the rolls are rotating at different speeds) and cut if the rolls are fluted (grooved). The theoretical capacity of a roll mill, Q (m^3/h), is given as Q=60*s*N*L*10^9, where s=rotational speed (rpm); N=the gap between the rollers or `nip'(mm); L the length of the working surfaces of the rolls (mm). In fact the practical working capacity is 10±30% of the theoretical capacity (Sugden et al., 1999). Working rates of different mills (in kg/h/mmroll length) are given as two-roll mills, 1.5±2.5; four-roll mills, 2±6 and six-roll mills, 1.5±10.

<snip>

The peripheral roll speeds in brewery mills are often 2.4±4 metres/sec (8±13 ft./sec.). As a particle moves between the rollers so it deforms and, if it is brittle, its structure fails and it breaks up (Sugden et al., 1999). Rolls may move at different speeds, for example the faster may rotate at 1.25 the speed of the slower. Consequently a particle passing between them will be torn by shear as well as being crushed. As well as that the grooves, or `fluting' milled in spirals on the surfaces of the rollers can be arranged not only to increase the coefficient of friction between the particles and the rolls, but also to cut the particles (Kunze, 1996).

<snip>

5.4 Dry Roller Milling

A large number of types of roller mills have been, or are, in use (Kunze, 1996; Narziss, 1992; Sugden et al., 1999). `Dry' mills have some characteristics in common. The feed roll delivers the malt to the first pair of crushing rolls, across their full width, at a controlled rate. The rolls are designed to deliver the corns `end on' to favour their being crushed along their length with the minimumdegree of husk breakage. The rolls are often about 250mm(9.84 in.) in diameter (in wet mills they are often larger). As noted the rolls are usually fluted and may run at different speeds. Both may be driven but sometimes only one is powered, the `follower' being dragged by the friction between the grist and the moving, powered roll. Mill rolls may operate at 250±500rpm. The roll length increases with machine capacity, to a maximum of about 1500mm (59.06 in.).


<snip>

The simplest mills are single-pass, two-roll dry mills. These are relatively slow
working and are inflexible, being suitable only for well-modified malts, special malts or
rice. They are used only in small units, such as pub breweries. Gaps used are 0.6±1.0mm
(0.024±0.039 in.) and working capacities are 1.5±2.5 kg/h/mm roll length (a working rate
of 1 kg/h/mm roll length is almost exactly 60 lb/h/in. roll length). It seems that three-roll
mills (with or without screens) are no longer in use. The arrangement of the three rolls
was like the grouping found in five-roll mills (see below; Sugden et al., 1999).


Whew!

I'm about to finish a 9.75" diameter roller, I hope. I'm mounting the bearings now.

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Old 12-16-2009, 02:18 AM   #8
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Quote:
Originally Posted by bohdan987 View Post
curently iam working on 4.5" smoth oak rollers, i run some tests and i think it will work like a charm after i add a sprockets and a chain drive. its under DIY "woody 3.0xpr".
Watch the gap on humid days. I'll check out your thread.



Then mill I planned on building is going to be made of 4" pipe. I plan on running 12" a second. The reason for 4" rollers is so the math is easy. 4" rollers will have the circumfrence of 12.5". So 1 revolution a second is perfect, running the mill at 60 RPM.
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Old 12-16-2009, 02:24 AM   #9
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holly crap a 9.75" roller! is it gona be steel or wood, 2 or 3 roller desighn? its gona be alot of flywheel mass, you dona need a strong motor to spin that plus a big gear ratio.
good luck.

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Old 12-16-2009, 02:58 AM   #10
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It's stainless!

1) I bought a 12-quart stainless steel cookpot from Kroger's, on sale for $9.09.

2) I bought some 3/4" steel rod from Lowe's, along with a bunch of 20mm sealed roller bearings, which where on sale for $2.97 each (they're 6204-ZZ).

3) I used some scrap wood to make a 3" square mold that mounted a bearing in the middle, lubed it up, and poured it full of Bondo automotive filler to make my pillow blocks.

4) I drilled a 1" hole in the bottom of the cook pot and glued double-nuts around it, to hold 8-32 mounting screws.

5) I'm gluing 1/4-20 nuts (with big washers) around the top rim of the brewpot.

The screws will allow me to exactly center the cookpot around the 3/4" shaft, which I will verify by turning it slowly in the bearings. Once centered I'll lock it in with some Bondo or epoxy.

Finally, I pour it halfway full with concrete anchor cement, then saw off the top half of the pot.

That should give me a heavy, strong, large roller for about $30.

If I succeed I'll go back to Kroger's and buy another cookpot.

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