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In Memory Of Ginny

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Zen Roaster II
Although it doesn't much look like it, from the Zen I drum roaster (previous entry) came the Zen II drum roaster. It is more an extension of the idea behind the roasters, not so much the design itself. I wanted to address some the biggest "issue" from the Zen I - over engineering. This one I originally thought of as a proof of concept, keep it simple roaster. It is my daily roaster. In the same vein as the previous entry, I wanted to design around the following.

1) Be able to build it with "basic" equipment". Saw, drill, rivets. This one took also a circular saw (with "disposable blade" - you are cutting cement board after all - kills the blades) for the hardibacker cutting. Nothing fancy. The Zen I taught me this well, and this whole thing was built in about 2 hours (unlike the weeks the Zen I took).
2) Again I wanted to roast a pound. It turns out I can do over 2.5 lbs in under 17 minutes.
3) I gave up bean sampling for a really good view. Some of the photos show the glass pretty dark, but that is after I was a bit negligent with my burn out run. Most of the time the glass is as shown for the one with the beans.
4) Be on a 20 amp circuit
5) I have good ambient temperature measurements via a TC. Very reproducible results.
6) Be able to control the profiles. Unlike the Zen I, I have moved on to a 20 amp Variac, although I only control 9 amps at a time. More on this later.
7) Build for under $100. This one was even less expensive. Well, the variac was an addition $100. So under $200 I guess.

This time, the design started around 2 glass stove doors and the George Foreman drum. Both effectively fell into my lap when we had a house fire a few years ago. The stove doors were from the wood stove we had, and the basket was a "helping donation". Actually, the more I think about it, this roaster would not be if not for that house fire. The main material (hardibacker) I "discovered" when rebuilding the hearth for the new stove in the house. I saw the MSDS and had an epiphany that it would be a great roaster shell. Non-combustible, insulative, sturdy. Armed with those items, my love of self tapping screws and aluminum angle (I just don't have the tools and patience for stainless - lesson learned) I simply built a box around the drum the size of the doors.

I scavenged two 9 amp table top rotisserie heating elements for my heat source, a gang box and house hold switches for wiring and control (keeping it simple this time), an in-expensive 42 rpm motor and a variac and the Zen II roaster was born.

Let's see, materials:

16' 1" aluminum angle $20
two heating elements $2
42 rpm motor $15
screws - still had plenty.
Hardibacker - $15
Aluminum sheeting - $15
Wires, boxes, switches - $15
Roasting basket - free
Glass doors - free
Thermometer w TC - $20
Variac $110

The two main things I want to note is the importance of the aluminum flashing inside. Each wall I added flashing to trimmed off 1 minute off of a 1 lb roast. The hardibacker is great, but it does absorb heat to some degree. By putting the flashing in, much more is reflected back in. I can easily do 1 lb in 10 minutes (probably faster, but I don't care to profile that fast). The 2nd item is the speed of the motor. I started initially with the rotisserie motor that came with one of the elements. It was 6 rpm and I was happy. After a very short time it died and I replaced it with the 42 rpm motor. Holy mother of ?? It was like I had turbo charged the roaster. Given all things equal (preheat, bean amount, power input) a 14 minute 1 lb roast suddenly went to 9 minutes. Convection and radiative heat - WOW. A little after that I tested it to what I though was it's limit. 2.5 lbs of greens. The result was a great 16.5 minute roast, with an acceptable profile (1 st about 13 minutes) and still cutting power back at the end. I bet I could make 3 lbs. So, I guess that leads me into how I roast.

I always pre-heat to 350 F. More than that and the roast tastes scorched. So, I pre-heat at full power and load the drum. At temperature the beans go in and I flip the motor on (that small switch to the right). For a pound, the ambient temperature usually recovers in a couple minutes and I dial back to power on the variac to keep the temperature in the 375-400 F range up to 1st. A note about control. The two heaters are controlled independently. That way I can control the lower one as the roast progresses. By the time chaff is falling, the element is cool enough not to cause a chaff fire. Once I make it to about 10% on the variac, I turn off the back element (via that light switch on the left) and power up the bottom again, to about 70%. It keeps the roast moving but still does not ignite the chaff. Anyway, I continually have full power until 7-8 minutes. At that point the beans are yellowing and the temperature is rising so I have to reduce power. As in most classic drum roasting I have to anticipate 1st and really pull the power back or I will have it rip right through 1st and into 2nd. The ambient has moved a bit higher to 410-420 F. At just shy of 2nd smoke starts to show and I usually cut off all power and coast into my end point. Gloves (ove-glove) go one, out comes the drum and into the waiting bowl to the right. One comes the blow drier and 3-4 minutes later I have cool beans.

That's it. One POS KISS Zen II drum roaster (proof of concept, keep it simple stupid).
Alchemist attached the following image:
There's the interior. The two elements, the thermocouple, and the simple support the drum rides on.
Alchemist attached the following image:
Actually, there is a much better shot of the drum support. At 6 rpm it rode up that wire, but at 42 rpm, it just rotates at the bottom and is SOOOO quiet.
Alchemist attached the following image:
drum support[383].jpg
This is the other side of the drum mount. That is actually the coupler that went to the motor in the Zen I, mounted with a piece of square tubing. Oh, and not the use of self tapping screws. Did I mention "simple". No taps here. :) The drum just slips in and out and is held in place effectively by not having a reason to go anywhere. It is level and square.
Alchemist attached the following image:
drum mount[384].jpg

Edited by Alchemist on 07/31/2007 2:42 PM
The motor is mounted with a plate and again self tapping screws. And I kept the wiring "modular" for the proof of concept portion of this. I wanted to be able to test other arrangements. Aside from that, it is very simple to wire in.
Alchemist attached the following image:
This is a much better photo of the front while roasting. Some people roast by smell, and sound and profile, but when all is said and done, I STILL like to see the beans. I don't think you can have too much sensory input.
Alchemist attached the following image:
And that is it all loaded up and ready to roast. Not much clearance, but not much is needed.
Alchemist attached the following image:
And I guess, when we come to the end of it, here is what we get.

BTW, nothing like defending what shows, but the slight unevenness is NOT typical. This was a DP Harrar, and not even into 2nd. But it was the only shot I had.

Not as pretty as the Zen I, but I use it weekly with never a problem.

The NEXT roaster is on the drawing board. I hope to combine simple, efficient and beautiful into the next one, and of course take what I have learned from these roasters and make the next one even better.
Alchemist attached the following image:
Ahh ha... this answers my "why don't you use Zen I anymore" question.

Woo-hoo! s:2


To answer your questions, the smoke leaves completely on its own via the seam in the lid. It is not air tight and in the very classic sense, the hot air/smoke rises and leaves. That simple. I didn't add a vent stack because it was not needed. As I learned from the Zen I, don't fully design and build from theory. Design and build simple, the change as needed. Smoke removal design was not needed. The reason for the case is two fold. First off, I have found I like building from scratch, not modifying. 2nd, it was a proof of concept roaster, and part of what I was testing was the thermal properties of the hardibacker and it ease of construction. The prototype to the proof of concept did indeed use a grill case, but it leaked way too much heat (I am a BIG fan of heat conservation and efficiency) and insulating it, with all those odd angles, would have been more work than build this one from scratch. Build time, start to finish was about 2 hours. Finally, the wire hanger. I tried an aluminum angle with a notch at some point and it squeaked too much without constant oiling. The wire is silent. Again, classic KISS. What I DO plan to add is an afterburner for the smoke. I might use a small fan, but I might simply let physics do it's own thing let the smoke take the path of least resistance to the afterburner (nichrome coil) stack.
John, this design would have been my top choice it only the article had been better. Pictures I could see, and better building description. I know others feel the same, and its why it received an honorable mention instead of a prize.

What homeroasting needs is a 1-3 pound roaster that anyone can build using readily available materials and home shop tools. This design does that. And, it looks like you could build it fast, too.

Also, this design has a HUGE potential for improvements. With very little modifications you could:

Use an RK drum if you couldn't make a drum
Use another style of drum
Change from solid drum to ventilated for profiling
Add a ventilation system
Switch to faster responding nichrome coil heater
Switch to gas heat
Add a PID
Add a computer controller
On and on...

This is a great, 'breadboard' design. It's simplicity is its virtue. I can see more homeroasters building this design in the future. I hope you'll upload some better photos and assist others with their questions. Dan
John, I'm with Dan on the article being the limiting factor on this entry.

This is definitely a roaster we would like to have in our Archives. s:1

Could we possibly talk you into expanding the article somewhat so that the folks who will be admiring it can also have a step-by-step plan to build it?

We will work with you on getting around the one-picture-per-post limitation of the Forum software.



We have history but

clearly you had an idea when you started this particular project; it did not show through to me as an entry.

Your article was rough, vague and limited, photo's seemed like they were taken from the old Frankenstein set and you gave no real sense that you even cared about the entry.

I feel as though you tossed it up as an afterthought;

did not work for me.

In the same fashion Ed was surprised by my self criticism on the Zen I, it nailed it on the head that I tossed this entry together. I had no pictures of the building process (as I built it for myself, not anyone else), it was the last day, and I was highly pressed for time. Heck, that is why it was the last day. Honorable mention is cool although Grand prize would have been cool also B)

I would be more than happy to detail more of the building process, exact dimensions, etc. More than anything, I wanted to show the thought process involved in it.

Is there something in particular you would like to know about the building process?

Also, have no fear, Zen III will be well documented.

I am going to return the the Zen II and re-read the entire article and post more thoughts.
This was not a last place roaster for me at all; I don't want anyone to think that, actually far from it!


Edited by ginny on 08/17/2007 3:02 PM

This entry fascinated me as soon as I read that you had used hardibacker. Having worked with that stuff in the past ( Shock ), my curiosity alone kept me reading through to the end. Employing the principles of KISS really worked for me on the wire support.

This one definitely deserves a more detailed presentation and I do hop you will oblige. s:2

Eddie Dove

The South Coast Coffee Roaster
vita non est vivere sed valere vita est
Home Coffee Roasting Blog and Reference
The more I think about this, the more I wonder what is not clear. I am biased having built it and think it is all obvious. But everything is clear when you understand it. My error.

I too will re-read and see what I can add. I believe in hindsight you (all) will see just how simple it is. Then again, I may be wrong.
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