Driven MaltMill - differential rotational rate?

[Yavid]

Will doing some research into Malt mill design I came across a website for the "Maltmill grain crusher". On the website there is the following blurb:

For additional efficiency, in high volume operations, a Gear Drive Option (GDO) is available to drive the passive roller directly from the driven roller through precision-ground, steel gears. These gears have different numbers of teeth, to provide a differential rotational rate for the rollers.

I am wondering if anyone knows how many teeth are on each of these two gears. I am trying to figure out the difference in rotational rate.

 

[bohdan987]

Will doing some research into Malt mill design I came across a website for the "Maltmill grain crusher". On the website there is the following blurb:

For additional efficiency, in high volume operations, a Gear Drive Option (GDO) is available to drive the passive roller directly from the driven roller through precision-ground, steel gears. These gears have different numbers of teeth, to provide a differential rotational rate for the rollers.

I am wondering if anyone knows how many teeth are on each of these two gears. I am trying to figure out the difference in rotational rate.

i have no idea but iam using a chain drive with a 48 teath sprockets they are around 4" in diameter. because iam driving two rollers at the time on my mill i had to make a tensioner sprocket. i have pic in DIY section under "project woody 3.0xpr" maybe that can hellp you.

 

[Yavid]

Thanks for the reply. I've never quite understood the idea behind a three roller mill though. Excuse my ignorance but how does it work? It is my understanding that the gap between the two upper roller is fixed and that the adjustment is made by the lower roller, is this correct? Does the lower roller even spin? If it does what direction does it follow? Whats the advantage to a 3 roller mill?

Your mill looks awesome by the way. Very nice work.

Edit: NM, now I see that one upper roller and the lower roller are adjustable. I still don't really understand the concept though.

 

[-Nathan-]

I received a maltmill with the geared "passive" roller for Christmas, I will count and report when I get home.

-Nathan

 

[Yavid]

Awesome. Thanks Nathan!

 

[Yavid]

I also sent an email to Jack Schmidling Productions, Inc. who I believe make the MaltMill. Jack Schmidling just sent me the following reply:

One gear has 30 teeth and the other 32. Our reason for doing this had nothing to do with any advantage. It eliminates backlash caused by roller spacing when using 1.5" rollers so we could use off the shelf gears.

The "advantage" was pointed out by the late Dr George Fix. I have never known anyone to win a brewing argument with him so I included the serendipitous advantage in the description.

Jack Schmidling


So now I have to wonder: is there really any advantage to the differential roller spacing? Any thoughts?

 

[wilserbrewer]

This is interesting, likely gives a crushing action w/ a bit of shear as well to free the husk.

 

[BrewBeemer]

This is interesting, likely gives a crushing action w/ a bit of shear as well to free the husk.

You'll rarely find a gear or chain drive system with a 2:1 or other common ratio that will repeat the gear or sprocket pattern due to wear, add one tooth more and it becomes a even wear pattern. Leave automotive cam chains and cam gear drives out of this as they do make a repeat wear pattern. A "V" belt drive can get away without a set wear pattern. Same applies to a geared or chain drive primary on a motorcycle be it a 28:57 not 28:56 ratio, again an odd number preventing a set repeat wear pattern problem.
On the odd gear tooth count I see good in this as wisebrewer stated with the slight shearing action added. This I bet will also apply with a two or three roller mills with the driven rollers slipping a small percentage while crushing the grain vs the drive roller speed. The worse case with this is a stuck free turning driven roller which I would blame to a forced feeding or moisture content problem plus the steep angle entering with small diameter rollers vs larger diameter roller mills. The above manufacture flat stated the ratio gave him the proper off shelf parts to manufacture a mill. A smart cost saving manufacture besides a KISS system. Another idea would be a mill with only one tooth difference with a idler sprocket to maintain the proper chain tension, more to add by the manufacture in parts with an added cost.
JMO here, one mill that uses deep toothed gears to power both rollers for gap adjustment looks like a high wearing item I would not consider in a mill. Again JMO not a flame war starter. I'm guilty, I went over the top and paid to own a MM3-2 with nothing less but must send out the rollers to get case hardened after polishing and detailing the journals and rollers first.

 

[wilserbrewer]

I see good in this as wisebrewer stated

Thanks Beemer, I'll take that typo as a compliment.

wilserbrewer

 

[BrewBeemer]

Oops, me bad sorry boss brain to keypad error. This without a bier or two no less.

 

[Yavid]

Thanks to everyone for your replies.

I understand the original reason behind using two different gears on the MaltMill (ieff the shelf parts and even wear pattern). I am just not sure what to think about the differential roller rate's affect on malt milling. So far it sounds like everyone agrees that the small amount of shear produced could be beneficial.

The reason for my curiosity is that I am in the process of designing my own mill and I am wondering whether or not to try to go for a differential rate in the rollers. I won't be using gears so even wear is not a concern. Maybe I will try both ways and compare.

One other thing I am wondering: can anyone explain to me the advantage of a three roller mill VS a two roller mill? I have to be honest I don't understand the point of the third roller. Does the third roller even turn? As you adjust the third roller closer to one of the first two isn't it moving away from the other? Won't the malt just go through wherever the gap is biggest?

 

[BrewBeemer]

Check out the MM3-2 site, the first roller gaps fixed with all grain going thur the second set of rollers that are adjustable. I had the extra cash burning a hole and chose the larger 2" diameter 3 roller unit being I would be mad at myself owning a 2 roller unit. Even if it was a mental gain difference i'm the one to please. Now if your scratch building I would look into the 5MM
belt drive system with different geared toothed sprockets that are available. A simple wide bearing could be mounted as a belt tensioner. Down in Oz I recall one member built his mill with all fully sealed ball bearings vs these bushing design mills, way ahead in design JMO here. These bushing run in dust and dirt vs a sealed bearing design unit.
I would go with the low side on rpm's reducing flour production, make added time for a slower crush time, what's 15 minutes more vs a full brewing day in hours?

 

[Yavid]

I apologise for my ignorance but MM3-2? Sorry but I am not sure what that is. Could you send me a link?

I still don't understand how a three roller mill works. I get that the first two rollers are fixed and that the third roller is adjustable. What I don't get is that when you adjust roller 3 to get it closer to roller 2 it is moving farther away from roller 1. What stops the malt from going through the gap between roller 1 & 3 instead of between roller 2 & 3?

As for my scratch built mill: I plan to use roller bearings instead of the standard oil impregnated bronze bushings that most designs use. The size I've settled on is the same size as the ones used in that Australia mill you mentioned: 6203. This bearing is about the right size for a ø2" or larger roller plus it has the advantage of being cheap and very common.

It's funny that you mention toothed pulleys because that is also what I am planning on using (commonly called "timing belt pulleys" around here). In my current design I won't need a tensioner as I should be able to tension the belt by sliding the drive motor (actually a gear motor that I scrounged) back and forth. If that doesn't work I'll try your bearing idea.

As for the final drive speed I am shooting for around 150rpm. I'd rather build the whole thing bigger then to go faster.

 

[BrewBeemer]

With your replies I see your headed in the right direction, cheers my friend.
Check out the Monster Mill site below. I did go for the MM3-2 with 2" rollers
vs 1 1/2", they're both 6" long. I now see Fred changed the steel alloy plus has case hardening as an extra cost plus has them in stainless. I'll send my rollers out and have then case hardened at a friends business, call me cheap.
I would go with ball vs roller bearings unless you add the inner roller race to your design. The 6203 is very common, heck used as the belt tensioner pulley on my LandRover Discovery. Good thinking on the lower RPM's, rather the surface speed of the rollers. Post your progress of your build.

http://www.monsterbrewinghardware.com/mm-320.html

 

[Yavid]

Thanks for the link. That's a mean looking mill that you bought! I have to admit I still don't understand how the third roll is supposed to function though. As I mentioned before when you adjust roll 3 closer to roll 2 isn't it getting farther away from roll 1? Won't the malt just travel the path of least resistance (ie: through the larger gap)?

As for my mill: I am just trying to get a basic design nailed down right now so I can start hitting the scrap yards and start scrounging material. It'll probably be a while before I actually get anything built. I will definitely post pictures when the time comes though.

Also, I goofed when I said roller bearing, the 6203 is actually a ball bearing.

 

[Yavid]

Since my question about a three roller mill is a bit off topic from my original post about differential roller rates I have put a new post up in the forum. My new post is located here:

https://www.homebrewtalk.com/f51/3-roller-mill-vs-2-roller-mill-156374/#post1801028