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Homeroasters - Home Roasting Coffee Community » BUILDING A ROASTER » Drum Roasters

Who is here? 1 guest(s)

My heat gun / drum roaster:
zamunda	#1 Posted on 02/07/2021 11:16 AM
1/4 Pounder Posts: 155 Joined: November 17, 2020	Hello, I am finishing my prototype roaster: drum is from a washing machine and heat source is a Steinel heat gun. Drum is driven by an old motor lying around but has variable speed control: does the job quite nicely! The gun performs very well, enough power to roast 1-1.5 kg. However, since this is a prototype, based on my roasting experiences, I want to buy a dedicated motor and heating element. Any recommendation/tips here? Please let me know! Thanks and regards, PS: I would like to add images from my Mac, but the GUI does not allow to upload them? zamunda attached the following images: Edited by zamunda on 02/09/2021 3:41 AM
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JackH	#2 Posted on 02/07/2021 1:24 PM
Administrator Posts: 1809 Joined: May 10, 2011	You can also use a photo hosting site like Imgur.com for posting your photos. You are using the Attachment/Browse at the bottom of the screen? JackH attached the following image: ---Jack KKTO Roaster.


zamunda	#3 Posted on 02/08/2021 2:46 AM
1/4 Pounder Posts: 155 Joined: November 17, 2020	Quote JackH wrote: You can also use a photo hosting site like Imgur.com for posting your photos. You are using the Attachment/Browse at the bottom of the screen? Yes I used the Attachment/Browse option exactly as you did! Any ideas why this does not work?
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JackH	#4 Posted on 02/08/2021 7:47 AM
Administrator Posts: 1809 Joined: May 10, 2011	Browse usually opens a file window on your computer. Could something be blocking like antivirus? You might also try clearing your browser cache or trying another browser. ---Jack KKTO Roaster.


zamunda	#5 Posted on 02/08/2021 8:40 AM
1/4 Pounder Posts: 155 Joined: November 17, 2020	Hello, I temporarily disabled the adblocker, that helped for 1 image, however, I could not upload a second image with the adblocker disabled.
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JackH	#6 Posted on 02/08/2021 9:32 AM
Administrator Posts: 1809 Joined: May 10, 2011	You can click browse and it works for the first image. Clicking browse again should should pop up the file selection screen and you can add a second file to the list and so on.... Be sure not to use "Preview reply"-- it causes some problems for attached images. Also, watch your file names, no special characters or spaces. ---Jack KKTO Roaster.


zamunda	#7 Posted on 02/08/2021 10:57 AM
1/4 Pounder Posts: 155 Joined: November 17, 2020	Quote JackH wrote: You can click browse and it works for the first image. Clicking browse again should should pop up the file selection screen and you can add a second file to the list and so on.... Be sure not to use "Preview reply"-- it causes some problems for attached images. Also, watch your file names, no special characters or spaces. I could add 2 images more but it remains buggy I think, adding another images does not work. Strange...
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renatoa	#8 Posted on 02/08/2021 11:10 AM
Administrator Posts: 2415 Joined: September 30, 2016	Confused... is the roaster on the workbench the 1.5 kg capacity, with a drum from a washing machine ? It should be 10 litres or so for this task... The other two images are CG.


zamunda	#9 Posted on 02/08/2021 2:46 PM
1/4 Pounder Posts: 155 Joined: November 17, 2020	Hello, Yes, the prototype on the workbench holds a drum from a washing machine, it is about ten liters. What do you mean with CG? The are rendered images from Solidworks I would like to post more images but having trouble with uploading.
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renatoa	#10 Posted on 02/08/2021 3:04 PM
Administrator Posts: 2415 Joined: September 30, 2016	CG = Computer Graphics, yep, rendered... A typical washing machine here is 50-60 litres, those rated 6-8 kg of dry laundry. What model is this so tiny?


zamunda	#11 Posted on 02/09/2021 3:25 AM
1/4 Pounder Posts: 155 Joined: November 17, 2020	Hello This is a tiny model, there are also larger models, I guess it depends on the size of the household (single). The volume of this drum is 10.8 liters, it is perforated which makes it suitable for use with hot air IMHO. Is there a kind of "golden ratio" between drum volume and amount of kilos which can be roasted? Or is this a matter of testing? Thanks and regards! zamunda attached the following images: Edited by zamunda on 02/09/2021 3:33 AM
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renatoa	#12 Posted on 02/09/2021 3:51 AM
Administrator Posts: 2415 Joined: September 30, 2016	Nice small drum... 1:6 is the golden ratio, 1 kilo of greens needs 6 litres of hot air. The ratio is a consequence of the ratio of specific heat of hot air, and the average green bean. The later depends a lot on origin and moisture, so 1:6 could vary 10-12% up/down. If someone want to cram more beans in a given volume, the temperature needs to be increased, thus more chances of roast defects. The above assertions are right at normal pressure. Someone could imagine a high pressure roast system, but is out of our scope. So your finding is right, i.e. 1.5 kg is close to the limit. Jim Schulman has a recipe somewhere... quoting approximately from memory: load a sample batch, keep it at 245 C hot air, if no FC until minute 12 try again with 20% less beans, until FC appear in the min 8-10 window.


zamunda	#13 Posted on 02/09/2021 3:59 AM
1/4 Pounder Posts: 155 Joined: November 17, 2020	Quote renatoa wrote: Nice small drum... 1:6 is the golden ratio, 1 kilo of greens needs 6 litres of hot air. The ratio is a consequence of the ratio of specific heat of hot air, and the average green bean. The later depends a lot on origin and moisture, so 1:6 could vary 10-12% up/down. If someone want to cram more beans in a given volume, the temperature needs to be increased, thus more chances of roast defects. The above assertions are right at normal pressure. Someone could imagine a high pressure roast system, but is out of our scope. So your finding is right, i.e. 1.5 kg is close to the limit. Jim Schulman has a recipe somewhere... quoting approximately from memory: load a sample batch, keep it at 245 C hot air, if no FC until minute 12 try again with 20% less beans, until FC appear in the min 8-10 window. Hello, Thanks for this info, very useful!!! Could you say something on perforated vs solid drums? According to my limited experience (this is my first project), the perforation benefits the flow of air around and inside the drum but absolutely no scientific proof just empirical assumptions. Thanks and regards,
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renatoa	#14 Posted on 02/09/2021 4:01 AM
Administrator Posts: 2415 Joined: September 30, 2016	At 23 cm drum diameter I could imagine a TO as main heat source, in an oblique setup, drum at 45 degrees, placed inside in a 32 cm diameter oven, having the TO as a cover. Additional heat sources are required at the bottom of this oven, because TO alone at 1300 Watts is not enough for 1.5 kg of greens. Dump could be done by tumbling the whole oven, something like a concrete mixer. The TO cover should be articulated with a hinge somewhat.


renatoa	#15 Posted on 02/09/2021 4:06 AM
Administrator Posts: 2415 Joined: September 30, 2016	The post above (#14) was sent before reading your post #13. Well... I hate solid drums, I am sold to hot air roasting... Solid drum is somewhat as a heat exchanger and you are forced to play with two variables, heat and airflow, in a way that I can't manage... and I don't want to learn or love it Delivering a stream of hot air at constant temperature is much simpler for me, technological and understanding. But... it's a personal preference... the rest of industry seems not agree with me :) Edited by renatoa on 02/09/2021 4:14 AM


zamunda	#16 Posted on 02/09/2021 4:34 AM
1/4 Pounder Posts: 155 Joined: November 17, 2020	Quote renatoa wrote: At 23 cm drum diameter I could imagine a TO as main heat source, in an oblique setup, drum at 45 degrees, placed inside in a 32 cm diameter oven, having the TO as a cover. Additional heat sources are required at the bottom of this oven, because TO alone at 1300 Watts is not enough for 1.5 kg of greens. Dump could be done by tumbling the whole oven, something like a concrete mixer. The TO cover should be articulated with a hinge somewhat. Sorry for my ignorance but what do you mean with "TO" in this context?
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zamunda	#17 Posted on 02/09/2021 4:36 AM
1/4 Pounder Posts: 155 Joined: November 17, 2020	Quote renatoa wrote: The post above (#14) was sent before reading your post #13. Well... I hate solid drums, I am sold to hot air roasting... Solid drum is somewhat as a heat exchanger and you are forced to play with two variables, heat and airflow, in a way that I can't manage... and I don't want to learn or love it Delivering a stream of hot air at constant temperature is much simpler for me, technological and understanding. But... it's a personal preference... the rest of industry seems not agree with me :) I fully agree (based on my limited experience with gas and heat gun heating). Thanks!
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renatoa	#18 Posted on 02/09/2021 4:51 AM
Administrator Posts: 2415 Joined: September 30, 2016	TO = Turbo Oven The halogen lids used as ovens with a glass pot. 100% convection in its purest form. With some flavor of infrared, depending on tuning you made to the halogen "shower plate" The forum has a separate section for machines based on this heating method.

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