August 19, 2018 21:14:14


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View Thread » BUILDING A ROASTER » Drum Roasters
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I think I found a great motor deal for my 1 kg Stainless Steel gas roaster build
Got my cyclone motor (a 50 cfm Dayton 1/125 hp) hooked up to an AC speed control and that works well. Now need to put together the traffic cone, 5 gal bucket, and plumbing to handle the chaff removal/airflow duties.

Also made the front drum support spider. Detailed here:
I will probably be making a video of how the front support is installed and the drum spaced correctly from the front lid.
The site default theme is now fixed so no more "hidden" links.

KKTO Roaster.
JackH wrote:

The site default theme is now fixed so no more "hidden" links.

Thanks JackH - that is great news!

While I wait for my motor chain and gears, I've turned my attention to the chaff collector (which will also control roaster airflow and direct the roaster exhaust up a chimney). Photos and captions are here: (which also serves to test the link color. Still looks the same color to me.)
Is blue for me, but not underlined.
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renatoa wrote:

Is blue for me, but not underlined.
Perform a full page refresh (CTRL+F5) to force css reload.

Thanks, that worked! ThumbsUp

So my original post (about the "great motor" deal) turned out to be a bit of a wash since the single phase induction motor can't be speed controlled. So after thrashing about for a while, I decided to purchase three gears from China that will give me two choices of RPM speed, using an 04C chain. Photo of my eBay order below. This seller will combine shipping, so I went with the $20 expedited on one item in order to get it in a week or less.

The 50T sprocket will go on the drum shaft and if I put the 18T sprocket on the motor shaft, then my 155 rpm becomes 55.76 rpm. If I put the 20T sprocket on the motor shaft, I would get 66.6 rpm (which is very close to the 68 rpm which represents 25% less than the calculated formula found for my drum diameter: (1/2 way down the page)
You are stressing yourself too much about rotating speed of the drum, imo, it matters more for solid drums with high caloric capacity and thermal inertia, and less for tin made perforated drums.
For example, the extreme case, for a mesh/wire basket shaped as a drum, where roasting is made mainly from hot air, and almost zero from drum conduction, there is no difference if turned with more than 20-30 RPM.
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Perhaps, but clearly the drum RPM is clearly one of the variables that impacts a roast, along with temperature & airflow. I’d like my RPM to be in the proper “ballpark” so that I can manipulate the other two to modulate my roasts.
Airflow again is a great misunderstanding, if not correctly related to the source of heat.
For a true drum commercial roaster heat is coming from drum mainly, and transfered to beans by all the three methods.
For such home built perforated tin drums the heat comes from flame/radiator especially, very little from drum itself, and you need a transport for heat to beans, which is hot air.
A true drum commercial roaster store a lot of heat in the drum, and delivers it at beans loading without any airflow. Just imagine how much heat can store a solid cast drum with 10 mm thick wall , and weighing 7-8 kg... and this is an 1.5kg roaster, not a 5-10 kg unit.
For such machine gas is cut completely until TP, which happens about 2-3 minutes, over 100 C degrees.

For your build, or anything similar, trying to mimic such behaviour is a guaranteed recipe for failure !
Your drum has insufficient energy stored to maintain so slow temperature drop, you will see a sharp drop at charge, from 200 C to 100 C in 30 seconds, will panic and increase gas to compensate, but without airflow, because so was told, no airflow for a drum roast in the first minutes, and the result... drum overheating, tipping and scorching.
The same will happen with an automated roast system if trying to follow a profile from the internet of a roast done on a commercial machine. Less the panic part :)
The software don't panic, but will try to follow closely the slow temperature drop specific of a big drum machine, and this will be done by applying too much heat, exactly as "you" did above.

So what is the right way to follow for a right roast with such home built low inertia machine ?
Simply no more be obsessed about the "right" TP, there isn't such thing, it is a characteristic of the machine, and is nothing bad to have TP at 80 C and 1 minute.
Just think that the fluid bed roasters don't have TP at all ! And they seems to be very happy with their roast results...
As explained here:
the heat transfer from air to beans is an exponential function, and TP is simply a point of that curve, where the real beans temperature intersects with an imaginary BT graph, a virtual temperature evolution, because everybody knows that beans don't have 200 C at load, right ?
What about gas and air until TP, though... imo, you should maintain a minimal gas %, the same you used to preheat until 200 C, let's say 40%. And also maintain permanently a good amount of airflow, because for your design it is vital to have permanently a thermal transport agent, to get heat from drum and deliver to beans. Your machine is a primary convection machine, not a conductive one.
Without air, even the smallest amount of gas led to overheating of drum tin, with the undesired effects.

We didn't talk a lot about drum speed in the above rant... Grin exactly because it is the least important factor you should pay attention, ignoring another more important described above ThumbsUp
Edited by renatoa on 05-04-2018 10:02
Great points renatoa. I believe it all comes down to finding the proper settings for whatever roaster one is using. Maybe I don't fully get something, but frankly, I don't see a great benefit to thermal mass (as you said, fluid bed roasters don't have a lot either). Thermal mass doesn't just intelligently decide to give up heat when beans are added. And any heat that thermal mass has absorbed, has been stolen in the first place from the roasting process. It just seems to me that I would rather have my BTUs roasting the beans rather than being stored in a big heat sink.

Learning what your thermocouples are doing for your set-up and not comparing them to a completely different set-up seems common sense to me. To do otherwise would be an apples to oranges comparison. I think the experimentation with exhaust blower speed (and therefore airflow) along with measurements of bean and exhaust temps (at the roaster) at particular gas burner settings should be fun.
I found this explanation in an old thread on Facebook Coffee Roasting Forum (of the air flow as it relates to the thermal mass of the system) and I think this helps me picture what is going on a lot:

"Air flow is simply a way to transfer heat.

The metal parts of the roaster store heat energy. Similar to a battery.

Turn up the air and it will draw heat from the store of energy and hopefully transfer to the beans Do it for too long and the store/battery will go flat. Therefore you need to turn up the gas to keep the store fully charged.
The advantage of stored energy is that it is available almost instantly unlike turning up the gas.
Moving air is more efficient at transferring heat than static air.
So with some basic knowledge of your system you should be able to add heat energy to your beans by turning up the air for a limited time without having to wait for the heater to add energy to the system.

So. If the roast seems to be going a bit slow I open the air and turn up the gas to speed things up.
As I approach first crack I add more heat to the system/battery by increasing the gas in anticipation of turning off the gas before the roast has finished and using air and the stored energy to continue the roast.
A heavy drum and machine will make a great heat storage system a opposed to a light weight drum and machine."

Good explanation?
pixelsmithy wrote:
EDIT: Just looked at your link and that is the motor that I started with (only mine was not a double drive shaft). It has plastic gear motor gears in the speed reducer and (if it drives it at all) will not last very long, I fear. I found mine on Amazon under the Uxcell brand name, available in various RPM configurations (gear reducers on the same motor)...

Unfortunately you was right... finally got a reply from "german" seller, after opening a paypal case because he didn't responded nor shipped the motor for almost one week. Wondering if they really stock them...
Incredible how these guys are hidden now under german company names, we are luck they still keep signing with their real names...


The gear is plastic. We will cancel your order and return the money to you.

Best regards,

Yinan Miao

Eckstein GmbH

Brauhausberg 12a
38678 Clausthal-Zellerfeld

The big question is that I am out of options to find a decent price motor in the 80 rpm range, at least 1N.m torque... :(
Sent you a message renatoa.
Not sure if anyone is interested, but here are a few follow-up images of my progress so far on the stock pot lid (roaster face). Info in the captions.
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