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Drum Roaster Modification
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allenb |
Posted on 05/21/2010 3:39 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
I'm in the middle of refurbishing my 1/2 drum roaster and thought I'd post the steps with pics for anyone interested in seeing the innards. The project will accomplish the following: -Change from perfed to solid drum -Change from heatgun style under-the-drum element to serpentine heavy ribbon under-the-drum which will allow non-powered (natural) convection or slight induced draft. -Change from C-frame "canopener" gearmotor to quiet synchronous drive motor. Here it is before pulling it all apart.
allenb attached the following image:
Edited by allenb on 05/21/2010 3:41 PM 1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 05/21/2010 4:02 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
First step was to build a heating element chamber with serpentine ribbon. The element and enclosure is similar to a bread toaster arrangement which some of the electric Probat sample roasters used although they used coiled resistive wire instead of ribbon. For simplicity I decided to just attach the element enclosure directly to the inside surface of the bottom cover. With this arrangement, to inspect the element you just remove the bottom and pull two wires from a terminal strip. The enclosure is constructed of mica board. The two end plates are .0625" thick and the long plates are .015" thick. To allow expansion without much warping I used a mortise and tenon style construction. The ribbon is typically used for industrial infrared radiant panels and is around 1/32" thick. Wattage per element is 400 x 2 for a total of 800 watts. I was shooting for 900 total but would be pushing the watts/sq. in. for these elements. Distance from the top of the elements to bottom of drum is 1/2". The bottom cover is drilled for natural upward convection. I'll post more as it progresses Allen
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 05/21/2010 4:07 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
Here's a pic of the element before installation.
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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beanflying |
Posted on 05/21/2010 9:00 PM
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1/4 Pounder Posts: 56 Joined: April 23, 2010 |
Nice little roaster :) When you say induced draft what have you been using for airflow control in the past or has it just been natural flow past the perforated drum and out the top? My name is Tim and I have a coffee equipment addiction problem :)
Two Hottops - modded TJ 067 Electric 1kg 5+years old Insert new 5-8kg Roaster here urgently |
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allenb |
Posted on 05/21/2010 11:09 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
I should have covered the previous heating arrangement details. Just below the drum was a 2" dia metal tube that spanned from the front of the roaster back to within 2"of the rear where a 3.5" muffin fan pressurized the rear 2" deep plenum. Just below the drum within the tube was a 1200 watt nichrome "blowdryer" or heatgun style element. The tube had a 5" long slot aiming up at the drum. A big problem was an inconsistent temperature output along its length. The temperature at the very front of the tube which needed the most heat due to having a larger mass of beans (agitation vanes spiraled forward) had less heat than the middle and I could never remedy this. Convection flow path was up through the drum holes, back through the drum back plate rear holes and up through the stack seen in the photo. Chaff would fall into a collection drawer which you can see the front of in the photo. I'll be removing the "stack" and installing a plate over the hole. The new flow path will be like a standard shop roaster...under the drum, in through the drum rear perforated back plate, out through the charging funnel. In this case the exhaust will be pulled out of the top of the charging funnel via small exhaust duct placed in close proximity to the opening. All air flow will be either induced via negative pressure at the charging funnel or just natural upward convection. If things work out well with the alterations I'll alter the charging funnel and add an exhaust duct going from it back to a cyclone separator/vac unit. All control was manual via dimmer control over the convection element. Allen 1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 05/27/2010 8:48 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
Change from perforated to solid drum The decision to change from perforated to solid drum was pretty simple. With the change from forced air to open element, natural convection it would not be good to allow smaller chaff and other particulates to drop down into the ribbon element where it could burn and smolder. I used 22 gauge cold rolled sheet metal to wrap the drum and secured it in several locations using SS machine screws with lock washers and nuts. The fun part was rolling the shape on the drum and keeping the edges in line with the drum. To accomplish this I would form a bit, add a couple of screws, roll some more... Here is a before shot:
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 05/27/2010 8:50 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
Here it is with new skin:
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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Ringo |
Posted on 05/27/2010 9:12 PM
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Pounder Posts: 474 Joined: January 14, 2010 |
Allenb Thats a really great looking roaster, looks like it was made in a factory. I believe the changes are cool. I believe soon you will have a great roaster.
All you need in life is ignorance and confidence, and then success is sure. Mark Twain
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allenb |
Posted on 05/27/2010 9:12 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
One of my worries is if the new layer of sheet metal will cause too much of a reduction in heat transfer to the beans. I know that many Probat shop roasters use double wall drum construction with an air gap to lessen conductive transfer and allow more convective transfer but I'm not going to be shoving a lot of convective heat past the beans. I unfortunately have to wait till it's finished to find out. Next step is to install the new heating element/bottom cover, insulate with high temp mineral/glass insulation and then reassemble. Another shot of the drum:
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 05/27/2010 9:22 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
Quote Ringo wrote: Allenb Thats a really great looking roaster, looks like it was made in a factory. I believe the changes are cool. I believe soon you will have a great roaster. Thanks for the compliment! It's amazing what an ultra thick layer of green powder-coat enamel will cover up in body construction goofs. Actually, I had the resources at the time of this build to hire a sheet metal shop to weld the aluminum body together. I would have made hash of it if I fabbed it. I'm equally looking forward to reports on your new rig in operation. Keep the photos and progress posts coming! Allen 1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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beanflying |
Posted on 05/28/2010 8:36 PM
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1/4 Pounder Posts: 56 Joined: April 23, 2010 |
Any thoughts on if reverse fins are needed in the drum to halp with good agitation or doesn't it matter as much at this size? The change in chaff handling will be interesting too, unsure but you may need to blow the drum out with air every few roasts as I think you will get chaff between the inner and outer drum layers ? My name is Tim and I have a coffee equipment addiction problem :)
Two Hottops - modded TJ 067 Electric 1kg 5+years old Insert new 5-8kg Roaster here urgently |
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allenb |
Posted on 05/28/2010 10:11 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
Quote beanflying wrote: Any thoughts on if reverse fins are needed in the drum to halp with good agitation or doesn't it matter as much at this size? The change in chaff handling will be interesting too, unsure but you may need to blow the drum out with air every few roasts as I think you will get chaff between the inner and outer drum layers ? During the original build I found I didn't have enough space to add helical return vanes due to the trier so I added a sloped return plate that is actually pretty effective in getting the pile to re-circ back to the rear of the drum. For chaff removal the plan is to go natural convection up to a BT of 350F then draw at the charge funnel with my chaff collector exhaust via small fitting that will set atop the funnel at a fixed distance (will design as I go). The plan down the road is to remodel the charge funnel with an exhaust tube going from it back to a cyclone. As far as chaff/stuff getting stuck between the sheet metal layers, I'm hoping that I have such a close fit (can't see any daylight between the layers), that it won't be an issue. Time will tell. Good points you bring up and I know well that most of us, especially me, can't see the lurking design flaws till we crank the heat up then we do the "doh"!
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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beanflying |
Posted on 05/28/2010 10:29 PM
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1/4 Pounder Posts: 56 Joined: April 23, 2010 |
Quote can't see the lurking design flaws till we crank the heat up then we do the "doh"! Very true ;) Just trying to eliminate some potential problems ahead of time with my designing too by learning from others trials and tribulations. My name is Tim and I have a coffee equipment addiction problem :)
Two Hottops - modded TJ 067 Electric 1kg 5+years old Insert new 5-8kg Roaster here urgently |
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allenb |
Posted on 05/29/2010 4:25 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
I finally got the new (used Bodine) synchronous 72 rpm motor to work on the 1/2 lb'r as a direct drive. Had major issues trying to go with a rigid metal coupling. It seems the synchronous variety produces a bit of 60 hz vibration at the shaft location which you can't really feel but unfortunately makes a bit of 60 hz racket that transmits down the shaft. After all, I was going through this drill to get away from the electric can opener sound. I ended up using a nylon reinforced 1/4" ID fuel hose that was a very tight stretch fit over the two 5/16" OD shafts. The Bodine motor shaft had a pin going through the shaft which caused me to have to notch the rubber hose to slide past it. This setup is a total success! No noise at all, very solid drive (can't stop it by grabbing the drum and most of all, the synchronous motor is able to start without having to allow rotation slop to get it up to speed. Now if the hose holds up for at least 50,000 miles I'll be a happy roaster.
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 05/29/2010 4:27 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
Another shot:
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 05/29/2010 4:28 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
One more:
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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muddyfeet |
Posted on 05/30/2010 1:46 PM
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Newbie Posts: 47 Joined: November 16, 2009 |
allenb- That's a lovely roaster! Your previous forced-hot-air-against-perforated-drum heating strikes me as really a novel idea combining air management, heat, and drum roasting in one system...which is a common goal around here, right? I also roast with a naturally-convected, 800w element-heated drum. I think you'll have enough heat transfer with the solid drum after a good preheat, but I'm guessing the airflow will stagnate and hinder chaff removal. When your BT hits 350, I would think the fast air replacement from a vacuum chaff collector would kill the roast right then- unless that's the point and you want to begin cooling while still in the drum. Maybe the solution is a post-roast chaff seperation? I'd also be worried of chaff sticking in the holes and creating a lot of smoke as it smolders roast-after-roast. I like the sloping bean-return chute. That's a great solution to bean return in a smaller roaster, and it lets you stick the trier inside the drum too! Congrats on the smooth motor upgrade. I'm curious about that bodine synchronous motor (as i'm using a bodine c-frame gearmotor right now). Does it require any type of controller circuit, or is it direct-wire to line voltage? |
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allenb |
Posted on 05/30/2010 8:49 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
Quote kmichaeldoc wrote: allenb- I also roast with a naturally-convected, 800w element-heated drum. I think you'll have enough heat transfer with the solid drum after a good preheat, but I'm guessing the airflow will stagnate and hinder chaff removal. Congrats on the smooth motor upgrade. I'm curious about that bodine synchronous motor (as i'm using a bodine c-frame gearmotor right now). Does it require any type of controller circuit, or is it direct-wire to line voltage? kmichaeldoc I would have probably stayed with the up-through convection setup if I just had more room to work with but I could not get the forced air setup to provide a consistent temperature from front to back of the drum so it was either moth ball it or go lower tech to a basic toaster design. I've used the natural convection before and got good results so I'm pretty confident it will do a good job. The ribbon element will provide enough heat transfer to the air to allow a low cfm draw across it and still stay in the upper 400's F so shouldn't be a problem when I pull some exhaust out the top. Time will tell. As far as chaff removal, if it turns out it hangs around and won't travel out the top I'm ok. I'll just have to clean up the roast afterward which I'm used to with some of my other contraptions. As far as the Bodine synchronous motor circuitry, it only requires an RC circuit across the input terminals (120 V). For this one it was a 20 watt 400 ohm resistor and a 250 volt 2 microfarad cap. You can easily reverse rotation by inserting a switch between two leads which could be useful for anyone wanting to keep the coffee moving toward the rear of the drum during roasting and out the front to dump. I've been watching your build with interest and looking forward to seeing more posts with photos. I like the swirl patterns on the skin! Allen 1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 06/24/2010 7:36 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
Ok beanflying and kmichaeldoc, if you don't mind, I'm going to consult with you guys before I modify any more roasters. The change to solid drum was a total bust. Maybe with a gas fired rig I could have gotten enough heat transfer but with less than 1kw of electric it couldn't get out of the starting gate. Another problem was chaff removal or the lack of with natural convection and even when assisted with a small amount of negative draft. The chaff ended up working it's way through the front drum gap more than I could live with. So, off with the outer drum wrap, back to perfed drum, scrapped the natural convection element and redesigned the forced air convection style heat source to allow an even temperature down the length of the drum. I ended up buying a 10 dollar harbor freight 1200 watt heat gun for the heat source which is working out well. At present the roaster is producing great coffee! Here's a pic of the heat gun core after tossing the body.
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 06/24/2010 7:41 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
I slotted a 1.5" dia brass sink drain tube for the convection plenum. This is mounted to the heat gun tube via hose clamp. The end is capped with a piece of sheet metal screwed to the tube.
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 06/24/2010 7:45 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
View from the bottom without slotted tube.
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 06/24/2010 7:46 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
Another bottom view
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 06/24/2010 7:47 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
Back end showing fan end of heat gun
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 06/24/2010 7:48 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
Internal before attaching slotted tube
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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allenb |
Posted on 06/24/2010 7:49 PM
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Administrator Posts: 3858 Joined: February 23, 2010 |
With slotted tube
allenb attached the following image:
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
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