A thought I had the other day...

ThatCoffeeBlog

I don't really care where comments end up... here or on the blog...

-bry

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Bryan: I'm just guessing here, but my thought would be that conicals simply don't generate the same amount of heat. I'm guessing that temperature is more of an issue than heat, anyway, and that they won't reach the same temperature as flat burrs, not matter how much heat the larger mass will hold.

If you turned a hand mill all day long it wouldn't really get all that hot at all. Warm, and that's about it.
Kind of my thoughts on the matter as well, but I'm curious to see what other people have to say, and also if anyone has ever actually PERFORMED experiments regarding this subject.

-bry

Fraser Jamieson said:
Bryan: I'm just guessing here, but my thought would be that conicals simply don't generate the same amount of heat. I'm guessing that temperature is more of an issue than heat, anyway, and that they won't reach the same temperature as flat burrs, not matter how much heat the larger mass will hold.

If you turned a hand mill all day long it wouldn't really get all that hot at all. Warm, and that's about it.
i think there is a couple of alternate with flat burrs: when made by ceramic or titan-alloy, absorbs less heat. bigger diameter works faster, therefore absorbs less heat. remember!, the motor also transfer heat, not just the friction.

another important thing is that, the flat burr grinder gives more small practices (causing tigger stripping) than conical due to high speed. that will increase body and bitterness slightly.

I'd like have a Robur or K10, but now i'm working with flat and able to make delicious espressos.
i'll have a k-10 in the next couple weeks (hopefully a doserless if they'll hurry up and ship the damn things). i'll let you know what i think.
mark koncz said:
...remember!, the motor also transfer heat, not just the friction.

I recall discussions and testing that concluded the motor is the major culprit of the heating. The higher powered slower turning electric motors of the big conical burr grinders heat slower and hence the advantage realized, but not so much from the burrs versus flat but the motor dynamics. A smaller powered motor required to do the same amount of work (grind X shots) will heat much faster than larger. But, once heated the larger mass motors takes longer to cool and can become a disadvantage, hence active cooling (vented and even internal fans).
You would think that dual-wall insolation/isolation+heatsinking would be a simple solution to managing the heat amassed and retained by the larger motors. Seems more proactive and less expensive than active cooling.
I've not done any experiments, though sounds like a great reason to justify purchasing an IR thermometer :)

As I understand, the heat generated by the burrs is due to friction from the burnishing action... so sharp burrs run cooler than dull burrs. So assuming burrs are appropriately sharp, slower turning = lower heat generated = lower temperatures. You are correct, though... if heat produced is equal, larger mass = lower temperature, heating up slower but staying at that temperature longer.

The motor discussion is interesting. Jeremy, you are correct that isolation and fins are cheaper than active cooling. The thing to remember with fins though is that they transfer heat by conduction... so they need to be in contact with the hot part to function. This makes them ineffective in cooling the rotor of the motor. Also, since the grinding burrs are attached to the steel motor shaft, heat in the rotor will be conducted right up to the burrs, regardless of how much insulation there is between the motor itself and the grinding chambers.

The benefit of fan-cooling is that it can remove heat from the hot rotor before it conducts up to the burrs. The other benefit is that you can modify an existing grinder to add a cooling fan... a little harder to add fins.
Large mass aluminum body components, essentially the bulk of the casing, could be used as heat sinks+fin ventilation to draw away heat before it had a chance to become substantial. It's an interesting idea. I agree that once you reach a point where the heat is a problem, direct drive equals direct heat transfer; but with good proactive heat management, we'd have to be talking about some crazy high volume.

Brady said:
I've not done any experiments, though sounds like a great reason to justify purchasing an IR thermometer :)

As I understand, the heat generated by the burrs is due to friction from the burnishing action... so sharp burrs run cooler than dull burrs. So assuming burrs are appropriately sharp, slower turning = lower heat generated = lower temperatures. You are correct, though... if heat produced is equal, larger mass = lower temperature, heating up slower but staying at that temperature longer.

The motor discussion is interesting. Jeremy, you are correct that isolation and fins are cheaper than active cooling. The thing to remember with fins though is that they transfer heat by conduction... so they need to be in contact with the hot part to function. This makes them ineffective in cooling the rotor of the motor. Also, since the grinding burrs are attached to the steel motor shaft, heat in the rotor will be conducted right up to the burrs, regardless of how much insulation there is between the motor itself and the grinding chambers.

The benefit of fan-cooling is that it can remove heat from the hot rotor before it conducts up to the burrs. The other benefit is that you can modify an existing grinder to add a cooling fan... a little harder to add fins.
Agreed, this might be worth trying... but I'm pretty sure an electric or other fan would do a better job. Why?

Because, fins are great for drawing heat out of things they are in contact with. They are useless in cooling things that they are not in contact with - any tiny airgap renders them nearly useless. This is why there is often conductive grease under them in electronic applications - to eliminate any possible airgap. If I understand correctly, much of the heat in motors builds up in the windings. Since this is part of the rotor, which is in the middle of the motor and surrounded by an airgap, I'm not sure how effective external fins would be in cooling that hottest part of the motor.

What I'd think would work better is a "slinger fan" on the motor shaft, inside the grinder housing. This draws air over the motor, through the middle of the motor, and basically sucks heat out of the motor shaft. I imagine there are some grinders that use this fairly common part to keep it cool, but I haven't run across one yet.
That said, I generally agree that its better to use passive cooling methods vs adding another component, assuming they get the job done. Just speculating on why this approach isn't in use. Sometimes they haven't though of it, but more often they did and it didn't work. You gotta believe that adding several dollars worth of extra components to the grinder wasn't the design engineer's first choice...
I'm actually inclined to agree; but we all know how it goes...

I just cringe at the thought of the potential marketing point/hype and translation to consumer cost, though. Look at how Mazzer milked nearly an extra grand out of offering the doserless E grinders.

Brady said:
Agreed, this might be worth trying... but I'm pretty sure an electric or other fan would do a better job. Why?
Because, fins are great for drawing heat out of things they are in contact with. They are useless in cooling things that they are not in contact with - any tiny airgap renders them nearly useless. This is why there is often conductive grease under them in electronic applications - to eliminate any possible airgap. If I understand correctly, much of the heat in motors builds up in the windings. Since this is part of the rotor, which is in the middle of the motor and surrounded by an airgap, I'm not sure how effective external fins would be in cooling that hottest part of the motor.
What I'd think would work better is a "slinger fan" on the motor shaft, inside the grinder housing. This draws air over the motor, through the middle of the motor, and basically sucks heat out of the motor shaft. I imagine there are some grinders that use this fairly common part to keep it cool, but I haven't run across one yet.
agreed, a single fan in the grinder housing is the best way.
are these modifications really needed?

yes and no

no, because i believe in the knowledge of the manufactures. these engenieers working on that, better than i can (or we). if you have heating (or quality) problems due to high volumes, you need to buy much more serious grinder! or for serving high volumes you might need to hire an extra barista and an extra grinder and maybe an extra espresso machine (for the smooth operation and quality).

yes, because sometimes these modifications gives noticable differences and simple things can improve the original models. i'm also the kind of guy who like to get hands dirty, and like building something unique. the upgrade gives us fun and good experiment :)

Brady said:
Agreed, this might be worth trying... but I'm pretty sure an electric or other fan would do a better job. Why?

Because, fins are great for drawing heat out of things they are in contact with. They are useless in cooling things that they are not in contact with - any tiny airgap renders them nearly useless. This is why there is often conductive grease under them in electronic applications - to eliminate any possible airgap. If I understand correctly, much of the heat in motors builds up in the windings. Since this is part of the rotor, which is in the middle of the motor and surrounded by an airgap, I'm not sure how effective external fins would be in cooling that hottest part of the motor.

What I'd think would work better is a "slinger fan" on the motor shaft, inside the grinder housing. This draws air over the motor, through the middle of the motor, and basically sucks heat out of the motor shaft. I imagine there are some grinders that use this fairly common part to keep it cool, but I haven't run across one yet.

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