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Larry Cotton's 'wobble disc' heat gun build
Piotrkurak
Ditto on request. My 8 cup has bean jams caused by having a removable and adjustable screen. I ended up bolting it into position and non precision bending the beaters and doing other odd modifications.

My heat gun funnel has always been full sized covering the bottom
 
Spyderman24-7
Very 1st sifter I tried based on the size/build quality actually worked out so well I just stuck with it. The 'brand' is Thunder Group on Amazon and it's questionable at this point. This is the version up until a few yrs ago...

https://www.amazo...B001PZ9GU4

Nice/robust build quality, same diameter top/bottom and the tolerance between the screen/arms simply works well with every green I've used.

Fast fwd to the issues the joke of a pandemic caused and when I ordered 2 to have as a backup it was quite different. Even though it was branded as Thunder Group it now had the tapered design at the bottom.

https://www.amazo...B001PZ9GU4

Granted I can make any sifter work with my setup, but the newer type doesn't have the same fitment as what I first started out with. Thankfully over the past 5+ yrs I've bought a few of the original type to have/tweak based on probe location, etc. and still serve me well. To have a quality backup (as they will wear out) I found a high quality 8 cup on eBay at a solid price and will surely serve me well when I wear my current one out.

I do manage to get several yrs out of a quality sifter and batch size is always 200 grams. No doubt trying to do upwards of 1 lb will increase wear/friction substantially. The only real point of wear these days is the shaft/housing, but I plan to get past that by possibly finding some flanged ball bearings that I can press fit into the housing so the shaft doesn't eat away at those points. Otherwise, I am still quite impressed with the level of control/ consistency, predictability I have with what I've created. I have multiple points of temperature feedback to make adjustments in real time, can see/smell the development the entire time and built robust enough that it simply never lets me down. Back in the winter we had a 22 F degree day with 20-25 mph sustained winds, wind chill was estimated to be 8-9 F and I was roasting away. Didn't need to, just wanted to and it had no problem keeping up without even maxing out the heat tool and at that time I didn't have the 'pipe reducer' chimney, but that wind is what got me to thinking about what to add to maximize efficiency in those conditions.
Spyderman24-7 attached the following images:
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Edited by renatoa on 07/18/2023 4:08 AM
 
Piotrkurak
Local hardware store has a hillman fastener colllection with #10 silicone bronze T bushings and the gas RC buggy people have flanged ceramic bearings in dozens of different sizes, good to 500f

Your builds look nothing like my Larry Cotton clone but I add the workmanship is impressive.

Takes more than 30 minutes to roast a batch outside in the winter here in reno with resulting overcook of the beans. turning the heat up to 800f just scorches beans quickly
 
renatoa
Seems strange that such big flour sifters can't be found in Europe... we have here only tiny 10 cm diameter models, with a flat sieve on the bottom, no curvature at all... useless...
 
renatoa
Yet another wobble disk in action:

 
renatoa
Because there aren't such sifters in Europe, to inspect myself, I am wondering about the shape of the sieve in the bottom, is it flat or rounded, same shape as wires ?
 
wbbh
Mr. Cotten has several designs and recently did one that uses a kitchen strainer in place of the sifter:

 
allenb

Quote

renatoa wrote:

Because there aren't such sifters in Europe, to inspect myself, I am wondering about the shape of the sieve in the bottom, is it flat or rounded, same shape as wires ?


Rounded, same shape as curved plated rods. The video wbbh posted using a kitchen strainer instead of a sifter shows him using a round bottomed screen strainer with a vertical rim with a set screw for attachment purposes. I'm going to assume he drilled and tapped the set screw holes himself since I've never seen a kitchen strainer with set screws for attachment to other items.

A potential problem with using a kitchen strainer is finding or making the curved rods agitator with the proper radius.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
wbbh

Quote

allenb wrote:

Quote

renatoa wrote:

Because there aren't such sifters in Europe, to inspect myself, I am wondering about the shape of the sieve in the bottom, is it flat or rounded, same shape as wires ?


A potential problem with using a kitchen strainer is finding or making the curved rods agitator with the proper radius.


Yes, especially if if you use the wobble disk. Two paddles offset will work nicely and do not require as much torque to turn so they can easily handle a larger roast weight. The radius on the ends of the paddle are easily matched to the diameter of your sifter or kitchen screen diameter. As long as there is clearance to turn, matching the radius exactly is not critical.

I discovered this by accident when I built an early version of Larry Cotton's roaster that used a central paddle. I tried to clamp the two halves of the paddle to the sifter shaft. With the heating and cooling the paddles shifted to an off angle. The angled paddle actually worked better because it was pushing one side then the other. You can see it in the video below.



For attaching the paddle/disk to the shaft I would use the clamp Larry Cotton uses with his wobble disk or by putting bends in the shaft so the paddles cannot shift/spin if the fasteners loosen.
Edited by renatoa on 11/17/2023 10:56 AM
 
Piotrkurak
They supposed to spin that fast? Almost like a fluid bed.

I know Larry Cotton specified 100.rpm on the beater bars so you get about 400 agitations a minute but that looks more like 200 rpm
 
Spyderman24-7

Quote

Piotrkurak wrote:

They supposed to spin that fast? Almost like a fluid bed.

I know Larry Cotton specified 100.rpm on the beater bars so you get about 400 agitations a minute but that looks more like 200 rpm


To each their own, but way too fast for my style of roasting. For my setup (sifter) I'm averaging around 84 rpm, but more importantly I go by visual. Too fast and heat is being lost and the coffee will be airborne too long to really absorb much heat... too slow and you risk scorching, so I dial mine in for a nice tumbling action so the bean mass really distributes the heat nicely.

I look for a specific type of sifter and have never had any issues getting most of them to function well in stock configuration, as in no need to modify the arms to get a nice sweeping action.
 
renatoa
+1 for the analysis above about speed.
Hard slapping a bean does not make it behave fluid... rather break
 
wbbh
Roasting more coffee helps, that was a first roast, since then the aluminum foil extension was replaced with sheet metal. I did get several good roasts for a frankly cobbled together project.

A switch to a variable seed screwdriver/gear motor would allow speed adjustments. That roaster was a bridge between the Hottop, visible in the video behind the home made roaster, and a larger fluid bed roaster I built. Before retiring the sifter roaster.

The biggest headache was the paddles slipping on the round shaft. Also clamping the screwdriver so it would remain still for an entire roast. I used a socket bit in the screwdriver to turn a nut on the end of the paddle shaft. This allowed me to easily lift out the sifter and drum the beans into my bean cooler.

See: https://homeroast...post_73709
 
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