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The Sample Roaster Project
Dan, thanks for the explanation! s:1 Doesn't sound too difficult now...

I picked up a stainless canning funnel, so I have that as a starting point. Its a little too large for the Behmor drum, but I might use a shorter 'solid' stainless drum instead (aka kitchen utensil canister) so that I can make the entire roaster a little more compact. With a smaller drum, there would be room to have a cooling tray built into the burner cover/housing much like the commercial sample roasters. Only problem with the smaller drum is that it drops the capacity to about 14 oz. Not too far off the 1 lb. goal, though...
I'm looking to purchase a gear motor to drive this thing, and what I've settled on for the moment requires a "0.68 mfd (or uF if you wish) run capacitor." Problem is that I cannot find a "run" capacitor less than 1 mfd.

I'm wondering if it must be a "motor run capacitor" or if any 0.68 mfd capacitor with appropriate voltage rating will work? Can anyone with knowledge of such things give advice?

I hope it will work, the motor is cheap, continuous duty, correct voltage, and proper RPM... oh, and its not a shaded pole motor so I can vary the RPM later on... B)
If you have a non-polarized cap of the right value and voltage, you should be OK. However, with a run-capacitor, how will you vary the RPM later?

Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
I would just use the 1mfd. It is close enough. Run capacitors jump in 2.5 and 5mfd increments, so they can't be that touchy. I think it is more important that you use something made as a run capacitor. Besides capacitance and voltage, they have to be able to deal with a certain amperage, too.

Can't you just cut down the large SS funnel to fit the Behmore drum?
With a motor speed controller! :P lol!

I believe that it is a brushless motor, so it will require a variable frequency drive. Fairly trivial thing to build from RadioShack parts (if I understand it correctly, anyway)
Thanks for the info and advice! :BowDown: I know the 1 mfd run capacitors are available, so I'll give it a shot.

The stainless funnel could be cut down, but I'm probably going a different direction on the drum - solid drum instead of the Behmor basket. The solid drum is more compact and should help shield the beans from direct heat (the 18k BTU burner can't be throttled back enough even for the skillet method I'm using at the moment).


Dan wrote:
I would just use the 1mfd. It is close enough. Run capacitors jump in 2.5 and 5mfd increments, so they can't be that touchy. I think it is more important that you use something made as a run capacitor. Besides capacitance and voltage, they have to be able to deal with a certain amperage, too.

Can't you just cut down the large SS funnel to fit the Behmore drum?
So the gear motor and run capacitor arrived. Early tests indicate that its more than powerful enough and the 1 mfd capacitor works just fine. The motor is of the synchronous type, so it turns fairly slow on its own (the gear reduction looks like 5:1 or so). The motor is surplus, so it didn't come with much in the way of tech data or instructions. I'm not too familiar with synchronous motors and I'm not sure I can vary the RPM much if at all. No big deal... Its a sweet little motor though, very compact and whisper quiet.

Now to get on with finishing the drum! Grin
Aweseome progress! One thing to consider is if you can't vary the speed of the motor, you can have different diameter drums. A larger diameter drum will be move the beans faster than a smaller diameter for each revolution.

Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
I keep dragging my feet on this project. Every time I get worked up into a lather about getting my butt into high gear, I see something like this:

And it reminds me again that problems do not always require a 'new' and relatively complex "solution!" My stainless pot over a grill side burner looks pretty space age by comparison! Shock Worst thing is that it will actually roast some decent coffee!! Now what's gonna push me over the edge to finally build a drum roaster?? Shock lol!
Sounds like you still have some questions about the motor. The best primer on small motors, motors with gear reducers and the associated theories that I have run into is at:
do a search there for the file:
bodinehandbook all chapters.pdf
Good reading while you're roasting over the idyllic wood powered roaster ;~)

Edited by John Despres on 04/12/2009 5:42 AM
I have managed to carve out a little time to do some work on the drum:

The two main components are a stainless canister and canning funnel. The vanes and brackets were cobbled together from 1" wide strips of 0.080" aluminum (those massive pop rivets just happened to be what I had on hand, though 1/8" would probably have been better...).

The vanes are angled and twisted to help push the beans towards the back and away from the front opening while the roast is under way. The largest circle of holes in the back are placed right at the 'corner' of the canister bottom to allow chaff to fall out. At least that's the theory, anyway (and more holes may still be added).

The funnel is not attached yet, and I'm not sure I'll ever permanent fix it in place. It fits snugly on the canister, but allows me to remove it for easier cleaning and debugging at this stage. Batch size seems to be dictated by how far off horizontal the drum's axis is. Three quarters of a pound of greens seems to work fine without having a really steep drum inclination, but I have yet to determine if beans will spill out the front when expansion occurs during roasting.

I'm going to try and rig up some kind of contraption to allow me to run a few test roasts using the drum and motor assembly without any housing before I commit to a lot more metal work. My first attempt, with the drum chucked in my cordless drill, went nicely until the battery died just before first crack.... Shock :@
Oh, man! Died before first crack! Did you do an emergency dutch-oven on the stove finish?

Great to see progress!

Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
I did save it, grabbed the stainless stock pot I've been using and kept on cookin'. The roast turned out fine, although it has an odd sort of brightness that I wasn't expecting despite finishing up close to second crack. I'm sure it has something to do with the pause and subsequent temp drop right before first crack...
This is exactly the drum roaster I wanted to replicate. I am interested to see if you have made any more progress on this build.
I was considering angling the drum about 10 degrees but I'm not sure its necessary.
What is the dimensions of your drum? and how much coffee do you think it will hold?
Sorry for all the questions but this is my first drum roaster project and I think yours will be a great "proof of concept" and building guide (If you dont mind)
Welcome Aaron! I'm glad you jogged my memory of this thread, since I've been attempting to get back into this project the last few weeks, trying to finalize the direction it will take. I didn't make a lot of progress in 2009... I've been happy with exploring the skillet roasting method, but with its extreme inconsistency I don't feel like I'm getting the most out of my beans. Even a small amount of repeatability will be nice!

Anyway, the drum that I have (in photos above) is about 5.25" inside diameter, about 6.25" tall (without the funnel). Using the assumption that you need 10 cubic inches of drum volume for each ounce of beans, the drum should be able to roast just under 14 oz. With the large funnel opening, the drum has to have a significant rearward tilt to keep the beans from falling out with 14 oz. in it. I suspect that it will work better with 8 to 10 oz. so that it doesn't need to be tilted back so severely. Stirring vanes that are angled to push beans back away from the front helps a lot.

Another tidbit while I'm thinking about it: I'm very likely going to switch to electric heat since the propane burner I have is way too much heat for a small drum. Even on its lowest setting, it will roast more than a pound in a skillet too quickly. The burner is over 5000W (18k BTU), for a small drum roaster I figure it should be less than 2000W. Besides, I'd like to add PID control at some point, and electric heat is much simpler to set up, from what I gather. I'm looking at 6" 1500W+ kitchen range/hot plate elements since they are cheap and easy to acquire (a nichrome element would be a nice option, too). Something along the lines of this:
cool idea, I think I'm going to stick with propane since the price of electricity in Australia is tipped to go up 60% in the next two years. Its good to get an idea of the size of burner though, I think I will make sure that I have the option of changing out the burners in the design in case I need to make adjustments.

Wow, been a while since I updated this thread...

Have made considerable progress (pics will be forthcoming) but the final appearance will be similar to this rendering:

I went back to the propane burner (10k BTU camp stove), built a new drum (holds a full pound now), and have a great deal of the aluminum housing completed.

Will also have controls/switches on one side, handles on the cooling tray for easier removal, and I'm going to try mounting the snout bearing on the inside of the front cover to keep up the minimalist appearance. The cooling tray will be ducted out the back for attachment to a shop vac.

If I can only keep up the momentum.... Shock
You are going to like having a one-pound sample roaster! I would recommend putting the snout bearing on the front. To me, it is more attractive than a hole in a piece of sheet metal. And, because it will be easier to oil. I put one drop of turbine oil on mine at the beginning of every roast session. Mine wasn't anything fancy, just a ring of 1/4" red brass. Nothing exotic like bronze or oilite. It has made hundreds of roasts and still looks good.

Electric stove elements are cheap, but they react slowly, so might be difficult for a PID to control.
I am going to try using a graphite impregnated bronze thrust bearing for the snout bearing; being much wider than what I have drawn, I'd like to hide it for aesthetic reasons... Should I go with something smaller, outside is fine. B)

While the stove element was a neat idea, I wanted faster response and knew the stove element would not provide it. After I found a suitable nichrome dryer heating element to modify, complete with ceramic insulators, searched for (but never purchased) a PID controller, and tried to build a manual heater control, I ended up going back to propane... Its about the adventure as much as the end result, right? ;)

Perhaps I will try to add PID control later on (with propane or maybe switch to electric heat) but I think for now manual control is fine for rudimentary profiles. It will still be way better than what I've been doing. Shock

I've been testing/using the drum (rotisserie-style over the good ol' grill burner) for a couple months now, and it is working great. Even in that set up, roasts have been way more controllable than the hand-stirred stock pot ever was!
A few pictures:

Still have a lot of work to do! :trink25:
Very nice fabrication.
Sean Harrington
Koffee Kosmo
Fantastic job
Hope its working to expectations

I home roast and I like it. Designer of the KKTO
Roaster Build information
Blog -

Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex,
(KKTO) Turbo Oven Home Roaster.
Gorgeous!!! -Scott
Excellent work. You put us all to shame! Now you just need to is connect up one of the new Arduino PIDs and you'll have the latest and greatest!
AWESOME dude!!

Simply beautiful art work!!!~

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