# Speed reduction on a commercial grinder?



## rich987 (Feb 5, 2018)

Anyone tried this? I believe most commercial grinders run at 1440rpm.

I read that lower grind speeds can give a better/different taste, if you don't mind waiting a bit longer for the grind.

Speed control on a single phase motor may not be that easy, but it depends on the type of motor used in the grinder.


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## Mrboots2u (May 10, 2013)

What grinder. You may need some of the speed to get the coffee from the burrs through the shute ( design dependent )


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## ajohn (Sep 23, 2017)

Flat burrs need centrifugal force to get the beans into the burrs. At least that is what manufacturers suggest when comparing with conical. Conical literally screw the beans into the burrs so don't need to turn quickly.

On the other hand flat burrs come in various diameter and all seem to run at the same speed so in principle could be slowed down. Most of the models seem to use conventional ac motors so slowing down would be tricky. If brushed it should be pretty easy also maybe getting rid of some of the speed variation there can be when they grind. Some of the speed controllers that can be bought for this type of motor may do that as they come.

John

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## 4085 (Nov 23, 2012)

ajohn said:


> Flat burrs need centrifugal force to get the beans into the burrs. At least that is what manufacturers suggest when comparing with conical. Conical literally screw the beans into the burrs so don't need to turn quickly.
> 
> On the other hand flat burrs come in various diameter and all seem to run at the same speed so in principle could be slowed down. Most of the models seem to use conventional ac motors so slowing down would be tricky. If brushed it should be pretty easy also maybe getting rid of some of the speed variation there can be when they grind. Some of the speed controllers that can be bought for this type of motor may do that as they come.
> 
> ...


Do not quite agree with your thoughts! Flat burrs do not need centrifugal force to get the beans into the burrs but to make the coffee once ground exit the burrs and into the chute. With most flat burrs, it has to be thrown out and into the grind chamber where you hope a lot goes down the chute, and some ends up staying in the chamber as retention. Cue to the Mythos, where the burrs and set at an angle of 45 degrees and because of this fact and the exit chute is at the bottom and not the side, the grounds have no choice but to fall via gravity.

Flat burred grinders do not all seem to run at the same speed! AM not even going to argue that one!

Conical burrs, because of their shape do not need centrifugal force as the coffee effectively makes its way down the length of the burr by adding more or by gravity as the burrs move. This in turn often means that conicals run much slower and by using simple mods such as the lens hood can be flushed out quite easily


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## MildredM (Feb 13, 2017)

The Monolith Flat is a little different in that I can adjust the speed. One of the advantages of this is thought that it can benefit, or not, the taste in the cup.

The burrs are angled, similar to dfk's description of the Mythos, and the exit chute is very, very short.

I have no idea of how it would affect a grinder that isn't designed to be slowed down. I'm pretty sure it has been done though.


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## rich987 (Feb 5, 2018)

Well I may try an experiment when I get hold of a used Mazzer or similar.

Speed control on single phase is not easy but for test purposes, I could just run the whole thing from a DC motor by some heath robinson method!

I am assuming the a Mazzer has an induction motor and not a universal motor?


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## Mrboots2u (May 10, 2013)

rich987 said:


> Well I may try an experiment when I get hold of a used Mazzer or similar.
> 
> Speed control on single phase is not easy but for test purposes, I could just run the whole thing from a DC motor by some heath robinson method!
> 
> I am assuming the a Mazzer has an induction motor and not a universal motor?


Old mazzer might not show u the improvements in the cup at any speed









Some of those have longer exit chutes , so they more you slow it down , the more likely coffee is to get " stuck "

Plus its a Mazzer .


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## ajohn (Sep 23, 2017)

dfk41 said:


> Do not quite agree with your thoughts! Flat burrs do not need centrifugal force to get the beans into the burrs but to make the coffee once ground exit the burrs and into the chute. With most flat burrs, it has to be thrown out and into the grind chamber where you hope a lot goes down the chute, and some ends up staying in the chamber as retention. Cue to the Mythos, where the burrs and set at an angle of 45 degrees and because of this fact and the exit chute is at the bottom and not the side, the grounds have no choice but to fall via gravity.
> 
> Flat burred grinders do not all seem to run at the same speed! AM not even going to argue that one!
> 
> Conical burrs, because of their shape do not need centrifugal force as the coffee effectively makes its way down the length of the burr by adding more or by gravity as the burrs move. This in turn often means that conicals run much slower and by using simple mods such as the lens hood can be flushed out quite easily


They were not my thoughts - as I mentioned "at least etc". Speed - the ones I have noticed do seem to all run at the same speed but very similar speeds would probably more accurate.

Perhaps many flat burr models have the burrs at some angle? No comment.

Afraid I will stick to my comment about conical otherwise my Sages would dose differently according to the amount in the hopper when I am using the grind timer. Having seen other larger burrs they appear to make use of the same feature and I will expect them to if I ever get my hands on a larger version. The Sage didn't for a brief period - turned out to be due to an oily hopper. I posted a thread on cleaning it in case some one else had the same problem.

John

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## Mrboots2u (May 10, 2013)

ajohn said:


> Perhaps many flat burr models have the burrs at some angle? No comment.
> 
> -


Not really of the commercial grinders I can only think of Eureka ones , and perhaps a San Remo one. Certainly all the older grinders Mazzer etc are flat , flat burrs.


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## 4085 (Nov 23, 2012)

ajohn said:


> They were not my thoughts - as I mentioned "at least etc". Speed - the ones I have noticed do seem to all run at the same speed but very similar speeds would probably more accurate.
> 
> Perhaps many flat burr models have the burrs at some angle? No comment.
> 
> ...


Where do I start.......have had lunch and thought about it a bit. John, if you want to come on herein share your thoughts, then that is fair enough, but remember, some people will read them and believe them, others will read them and think otherwise. You seem to be basing your thoughts on very low end grinders. At the end of the day, the Sage range of grinders are very low end in every way, and not really anything to base a discussion on. For example, the Sage Pro has a motor of 165 watts, the Ceado E92S is about 1 kilowatt and spins at 240 rpm.....that is what power does for you.

If they are not your thoughts, why share them?

The only other flat burr grinder I know of that is also angled is the Monolith. To me, that makes the practice in the minority, what do you think?

Your Sage might tick all of your boxes, but let me assure you, that beans fall into the burrs via gravity and weight pushing them through. Some grinders have an auger to help 'bring' beans in, but burr shape and spin speed play absolutely no part at all.....unless you know otherwise


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## GlennV (Mar 29, 2013)

To get back to the original question, almost all commercial grinders use induction motors. You can change speed by changing the supply frequency, but that doesn't work so well for single phase ones. Mazzer do make three phase grinders, and a variable frequency drive works fine for them - AndyS on here uses one to drive a robur I believe.


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## espressotechno (Apr 11, 2011)

Macap grinder speeds are 1400, 400, 350, 1600 across the range.

San Remo grinders are made by Fiorenzato.


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## themartincard (Feb 22, 2015)

Would reducing the supply voltage to a motor not reduce the torque that the motor generates as well?


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## 4085 (Nov 23, 2012)

themartincard said:


> Would reducing the supply voltage to a motor not reduce the torque that the motor generates as well?


If it did, you would struggle with light roasted beans


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## rich987 (Feb 5, 2018)

themartincard said:


> Would reducing the supply voltage to a motor not reduce the torque that the motor generates as well?


Nope, not with induction motors. You can control the speed to some extent with a VFD, if you can find one that works on single phase, but you can have problems with magnet saturation as the frequency drops.

A universal motor (series wound AC motor), which has windings in the rotor which are wired to the supply via a commutator, can be speed controlled with a triac (light dimmer).

A 3 phase grinder on a VFD would work great, but not sure I'd find one easily.

Regarding the comment, "it's a mazzer", are there better choices, secondhand for £200?


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## Mrboots2u (May 10, 2013)

rich987 said:


> Nope, not with induction motors. You can control the speed to some extent with a VFD, if you can find one that works on single phase, but you can have problems with magnet saturation as the frequency drops.
> 
> A universal motor (series wound AC motor), which has windings in the rotor which are wired to the supply via a commutator, can be speed controlled with a triac (light dimmer).
> 
> ...


No they are decent grinders , I am just not sure you will see a huge amount of benefit from slowing down the speed on these old grinders .

You would be better of making sure the burrs the parraell and aligned.


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## grumpydaddy (Oct 20, 2014)

I have a feeling that you need to play with the frequency rather than the voltage so looking for an inverter with such adjustable parameters could allow you to experiment.

Olde worlde machines using standard mains motors like bench drills and lathes seem to have gearboxes....likely for a reason.


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## 4085 (Nov 23, 2012)

I wonder how Monolith do it?

Introducing our Monolith Titan Flat burr single dosing espresso grinder with 75mm Titanium Nitride coated burrs and variable speed brush-less DC motor.......

The Monolith Titan Flat uses a brush-less DC motor rated for 40,000 hours life. RPM (rotations per minute) can be adjusted using dial on the side of the grinder from 22-800 RPM with a recommended top speed for light roasted, hard beans at around 600 RPM's.


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## ajohn (Sep 23, 2017)

themartincard said:


> Would reducing the supply voltage to a motor not reduce the torque that the motor generates as well?


It not this simple but with a brushed motor it's possible to retain the same power in. As it's running at a slower speed the current can increase to higher levels than normal. Just about all motors will take as much current as they need to reach a speed where their "parameters" balance. In the extreme any sensibly designed motor will burn out if it's prevented from turning at all or if overloaded for sufficinet time at any speed it happens to be running at due to the way it's being driven. Even then it isn't that simple. Motors are designed to have a rating. Some are continuous many more are not and will assume rest periods between use. Hence for instance Mazzers comments on the mini - low consumption and Jolly medium consumption and then the Major for medium / high consumption. That one also has larger burrs so needs more torque which means more power. The RPM of those are all the same. The duty cycle rating of the 3 varies.. Then comes the Royal that rotates more slowly and has an air vent for cooling. That may be using a brushed motor.. An alternative would be to gear a normal AC motor down and it could then use a lower power motor.

Mad example of rating. A chinese motor out of a type of exercise machine. It's rated at 2kw. In real terms that's probably a stall rating. It might take that for some seconds in practice. Some other motors out of other types of exercise motor might be rated at 1.5kw and that may even be more realistic as they are lot bigger and heavier.

Fans become a problem when motors are slowed down - they don't give so much cooling any more which will reduce the rating. Not that this is likely to matter on commercial machines used at home but it could in the extreme.

Variable frequency drive is more complicated. Usually easy from 240V as many motors can be rewired as they come from UK 440v 3 phase to another voltage used in the USA and it can be generated from a 240v supply. There are various other options in this area but perhaps that approach is the most practical one all round.

Afraid I get a bit dismayed when I see comments about grinder power that just don't consider anything at all really about it's intended use or size of burrs and grinding rates etc.

John

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## 4085 (Nov 23, 2012)

Am I the only one to think, another lecture!


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## Missy (Mar 9, 2016)

dfk41 said:


> Am I the only one to think, another lecture!


Yep... you're the only one...

I'm fascinated... i really got interested half way through.

Why would you want to reduce the speed on a fan motor? Surely fast spinning is what keeps me cool? Unless it's one of those handheld fans with fabric flaps... Too fast and you might lose a finger...

Or a wind tunnel fan in domestic use... You'd want to decrease the RPM on that incase your pot plants get defoliated.

I'd also be delighted by an exercise machine with a high torque motor...

I guess that means it runs itself while I sit on the sofa with prosecco and torque rubbish on the internet?

Anyway back to coffee.


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## joey24dirt (Jan 28, 2017)

Hook up one of these....










Do a temporary install and carry out some tests to see if it's worth having it in permanently


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## rich987 (Feb 5, 2018)

That's just a dimmer (triac or scr) chopper, ok on a universal motor, no good on an induction.


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## rich987 (Feb 5, 2018)

joey24dirt said:


> Hook up one of these....
> 
> 
> 
> ...


Sorry meant to quote this!

This is just a dimmer (triac or scr) chopper, ok for universal motors no good on an induction motor.


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## rich987 (Feb 5, 2018)

dfk41 said:


> I wonder how Monolith do it?
> 
> Introducing our Monolith Titan Flat burr single dosing espresso grinder with 75mm Titanium Nitride coated burrs and variable speed brush-less DC motor.......
> 
> The Monolith Titan Flat uses a brush-less DC motor rated for 40,000 hours life. RPM (rotations per minute) can be adjusted using dial on the side of the grinder from 22-800 RPM with a recommended top speed for light roasted, hard beans at around 600 RPM's.


Brushless DC motors are easy to control speed but not used much in domestic products other than by Dyson (who calls them digital motors!) and in the better battery drills. They are 3 phase motors with permanent magnets in the rotor.

Good torque at all speeds but usually run on lots of amps and not many volts so good for battery powered stuff. You vary the speed with variable frequency.

There are single phase VFD's but they are not cheap. Most are single phase in, 3 phase out.

Anyway, once I get my hands on a Mazzer or similar, I might see if its possible to try it at lower speeds, just for the hell of it.


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## joey24dirt (Jan 28, 2017)

Ah I thought it would work. I guess not. I'll rip out a VSD from work for you then lol


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## MildredM (Feb 13, 2017)

dfk41 said:


> I wonder how Monolith do it?


By voltage reduction/increase.



> Introducing our Monolith Titan Flat burr single dosing espresso grinder with 75mm Titanium Nitride coated burrs and variable speed brush-less DC motor.......
> 
> The Monolith Titan Flat uses a brush-less DC motor rated for 40,000 hours life. RPM (rotations per minute) can be adjusted using dial on the side of the grinder from 22-800 RPM with a recommended top speed for light roasted, hard beans at around 600 RPM's.


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## rich987 (Feb 5, 2018)

MildredM said:


> By voltage reduction/increase.


Not if it's brushless. Brushless is controlled by frequency. That's how you maintain torque at low rpm. (trust me I'm a doctor). If they did, it would be the worst design ever!

If you just put a DC voltage on a brushless motor it won't even turn! You run them with three pulsed DC signals, the pulses are synchronised to rotate the motor. This is the commutation and is performed by a processor/driver chip.

You can vary the voltage or pulse width and this will vary the torque not the speed.

An ordinary brushed motor can be varied in speed with different voltage but you lose torque as the motor slows down (lower current), this is why you don't use voltage to control brushed DC motor speed, you use PWM. This means you chop the voltage to the motor, so to slow it down you send the full voltage but only for a brief time (duty cycle). AC universal motors are controlled likewise, except you chop the AC signal on each cycle. Dimmer switches work like this.


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## MildredM (Feb 13, 2017)

Well, according to Denis it's via voltage. Maybe there's something more . . . resisting









Edit: I will just take it apart and have a look!


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## rich987 (Feb 5, 2018)

MildredM said:


> Well, according to Denis it's via voltage. Maybe there's something more . . . resisting
> 
> 
> 
> ...


OK, open it up and stick a scope on it! Brushless motor will have 3 wires unless it has hall sensors in...


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## MildredM (Feb 13, 2017)

rich987 said:


> OK, open it up and stick a scope on it! Brushless motor will have 3 wires unless it has hall sensors in...


According to Denis they have likely used PWM.


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## ajohn (Sep 23, 2017)

There are several types of motor around which can confuse things. Typically a universal motor would have a field winding so when excited with AC both field and armature see the same thing so they works as usual. It's possible to use a separate controller on the field as well but can be dangerous as the speed can get so high that the motor may explode. That can also be used to regulate power under various conditions. It how some electric vehicles I worked on controlled the motor but DC in that case.

There are also motors that have no field winding and use magnets instead. I didn't think these could behave like normal universal motors until I bought one that was. It used triac control arranged to keep the speed constant with varying load.








The chinese motors sprang to mind as some seem to be magnet types. They drive them by rectifying the mains and then switch mode driving them to set the speed they run at. Switch mode is just connecting and disconnecting the supply to the motor at some speed and varying the volts applied time. Bit of a problem for me as I bought one to use on something to go in a lathe toolpost that came with it's control gear but not the actual controller so I have no idea what voltage it should be run at.

Brushless, 3 phase and inverter drive are all similar in some ways. The brushless and inverter drive produce the phases with electronics and the speed can be controlled as well by altering the drive frequency. The hall effect thingy has been used to make sure they rotate the required direction but there are other ways of doing that. On some applications this approach can be cheaper than what has been used in the past - washing machines for instance. Maybe grinders too if the electronics can be simple enough. A fridge freezer we will be buying at some point also uses an inverter drive. Makes me wonder if some of these don't try to produce a typical AC sinusoidal waveform as a lot less bits would be needed to drive them.

John

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## rich987 (Feb 5, 2018)

MildredM said:


> According to Denis they have likely used DWP.


Dept of Work and Pensions?


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## MildredM (Feb 13, 2017)

rich987 said:



> Dept of Work and Pensions?


Stupid spell checker! It should have said PWM of course


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## MildredM (Feb 13, 2017)

This explains it very well.

(Thanks again to Denis).


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## rich987 (Feb 5, 2018)

MildredM said:


> Stupid spell checker! It should have said PWM of course


PWM works great on brushed motors. I am guessing the Monolith conical uses a brushed DC motor and the Flat burr version has the brushless.

You still use PWM on brushless, but only to control torque, not speed.


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## rich987 (Feb 5, 2018)

An interesting (maybe not interesting to many though!) point about motor speed control is closed loop and open loop speed control.

Brushless DC and  AC induction motors are controlled in speed by frequency so their speed is constant - it's locked to the frequency.

Brushed DC controlled by PWM does not have a constant speed - it varies with load. To fix that, you have an encoder on the motor so you can measure it's actual speed and compensate accordingly. Using PID! Which I know you coffee machine fanatics all know about...


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## MildredM (Feb 13, 2017)

rich987 said:


> PWM works great on brushed motors. I am guessing the Monolith conical uses a brushed DC motor and the Flat burr version has the brushless.
> 
> You still use PWM on brushless, but only to control torque, not speed.


Sorry. I thought the linked article said speed.


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## rich987 (Feb 5, 2018)

Maybe there's a market for a UK manufactured grinder with PID motor speed control to ensure the perfect grind...


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## ajohn (Sep 23, 2017)

rich987 said:


> Maybe there's a market for a UK manufactured grinder with PID motor speed control to ensure the perfect grind...


It can also be done pretty well by sensing the back emf behaviour when the PWM is in off periods. If a speed sensor is used to detect actual speed there are several techniques used depending in part if it's a tacho generator or some form of rotary encoder.

John

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## rich987 (Feb 5, 2018)

ajohn said:


> It can also be done pretty well by sensing the back emf behaviour when the PWM is in off periods. If a speed sensor is used to detect actual speed there are several techniques used depending in part if it's a tacho generator or some form of rotary encoder.
> 
> John
> 
> -


Yep, we used to do that in drives I designed the software for, but we found that our particular motors needed quite long off periods, so the PWM frequency was quite low. In the end we went brushless with hall sensors and we had industry leading speed control range on them. (I had a patent on that!)


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## rich987 (Feb 5, 2018)

Just won a Mazzer SJ, so looking forward to seeing what's possible with speed control/reduction.


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