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View Thread
Homeroasters.org » BUILDING A ROASTER » Drum Roasters
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Dereks 1-2Kg drum roaster build
dmccallum
Another test, this time with a flat Thien-baffle. Results didn't really vary between having it 130, 160 or 190mm from the bottom, but still 100% separation with nothing perceptible going through.
Will be much easier to make a flat baffle, I imagine with 4 tabs on the inside diameter that can be bent 90deg down for a jubilee clip to fix it place on the centre pipe.

I also ran a test with the chaff and no baffle (just straight barrel) and it didn't take long for material to make it through to the Dyson.

Everything to this point I've done with a Dyson on full draw. Next round and I'll try with some lower air-flow rates.
Just roughly how much air is drawn from the drum during roasting? Just enough so as not to suck beans out? Imagine this might be a difficult one to describe. Anybody?
dmccallum attached the following images:
imag1420.jpg imag1419.jpg

Edited by dmccallum on 10/09/2016 09:31
 
btreichel
Don't know, maybe someone can measure it for you, I don't have the set up. However, air flow through the drum has a primary impact on roast quality and control.
 
simwilldig
dmccallum wrote:
Everything to this point I've done with a Dyson on full draw. Next round and I'll try with some lower air-flow rates.
Just roughly how much air is drawn from the drum during roasting? Just enough so as not to suck beans out? Imagine this might be a difficult one to describe. Anybody?


I don't have any specific numbers on airflow volumes for your drum size, but you might find this airflow explanation helpful. https://youtu.be/... The general starting point for airflow that I have heard is relatively low for drying stage, relatively medium for carmalization and then relatively high from first crack on for development. However, I don't have much experience on a drum roaster with controllable airflow myself. I'm finishing up a 5kg drum roaster build and I have found that towards then end of the roast as the beans become lighter I can't open up the airflow too much or it starts sucking beans out.

By the way, thanks for sharing your design! Some day I hope to build a similar sized roaster and will definitely use this info.
 
dmccallum
Another few tests. This time I've bypassed the air draw to the extent that the input flow is very reduced (I can't imagine a roaster typically works with anything less than this). Still get 100% separation.
Have also simplified the input pipe making it flush with the cylinder wall. 100% separation.
dmccallum attached the following images:
tang_ent_flush_130_result.jpg tang_ent_flush_130.jpg tang_ent_130_low-draft_result.jpg vent_bypass.jpg
 
dmccallum
Thought I'd also try a straight entry configuration. San Fransiscan do this on the SF-1 with a baffle on side of the outlet pipe. I couldn't get this to work very well, the baffle appeared to disturb the air-flow and while still got near 100% separation, fines started to get through which I image would inevitably have to deal with downstream. I didn't pursue trying to improve on this.
dmccallum attached the following images:
straight_ent_center_baf_result_2.jpg straight_ent_center_baf_result.jpg straight_ent_center_baf_2.jpg straight_ent_center_baf.jpg
 
dmccallum
Another straight entry config this time with a baffle mounted against the exterior which did work much better, achieving 100% separation.
dmccallum attached the following images:
straight_ent_ext_baf_result.jpg straight_ent_ext_baf.jpg
 
dmccallum
I also experimented with an air-ramp. Not sure this added much and demonstrated that it'd need to be joined to both ext and int surfaces as material would collect on the upper surfaces.

A straight entry config with no baffle only achieved about 60% separation, so that's not an option.

The flush tangent entry with the Thien baffle at 130mm off the bottom appeared to work best. I'd run quite a few tests and didn't find any build up of fines in the Dyson at all. I guess there'd be some build up over time, but the exiting air-flow appeared very clean.

You can get your tangent entry cut pattern by using a 3D design package to make a template that you can stick to your cylinder before getting your dremel or whathaveyou out.
dmccallum attached the following images:
straight_ent_ext_baf_air-ramp_result.jpg tang_ent_with_ramp.jpg tang_ent_with_ramp_result.jpg straight_ent_no_baf_result.jpg straight_ent_no_baf_air-ramp.jpg straight_ent_ext_baf_air-ramp.jpg tang_ent_cut_template.jpg
 
dmccallum
Had been trying to establish the handrail-radius for the drum vanes and wasn't sure I was getting accurate answers from the formulas I've seen here (http://www.homeroasters.org/php/forum/viewthread.php?thread_id=4482&rowstart=40)

To get off on the right start you 'd have to establish an accurate input for P by following the line of your 25deg angled vane to the edge of the next quarter turn in circumfrence to get a quarter of the screws hieght. In my case 404.2 so total rise of 1616.8 for one complete turn.

Drum Outer Vane Vars
P=1616.8
D=240
d=220
h=20

Step 1
l = sqr ((pi*d)sq) + (Psq)
l = sqr ((pi*220)sq) + (1616.8sq)
l = sqr (477688 + 2614042)
l = sqr (3091730) = 1758

Step 2
L= sqr ((pi*D)sq) + (Psq)
L= sqr ((pi*240)sq) + (1616.8sq)
L= sqr (568489 + 2614042)
L= sqr (3182531) = 1783

Step 3
R= (Lxh)/(L-l) = (1783 x 20)/(1783 - 1758) = 35660/25 = 1426
r = R-h = 1426 - 20 = 1406

I don't quite get it, tried a number of different vars and have to wonder whether the method works well for what I'm trying to do - an R of 1426 is wide of the mark and I wasn't convinced with other results I'd got. There's also so the question of why I'd get a different answer for R when I repeat the formula for the inner vane set starting diameters of D=220 & d=200. R for the second result should be the same as r for the first ?!
Someone do us a favor and point out where my method/math has gone wrong.


So instead I've used Sketchup to do it for me. It's easy and you get a better feel for the result.

1. Draw a cylinder that represents the inside surface of your drum complete with a centre-line running through it, and then figure out your vanes start and stop points. Draw a straight line between them.
2. Find the middle point of the line and draw a line following the up-down (blue) axis to the cylinder centre line. The draw another line from the middle of the last line at a straight tangent (or in line with the one you just drew to the centre-line) to the surface of the cylinder.
3. Get the dimensions of the line between the vane stop/start points and the line to the cylinder surface and draw them out exactly.
4. Draw a 3 Point Arc starting from a Vane end point to the line that met the cylinder wall and terminating on the Vane end point.
5. Delete the small middle line connecting the straight line and arc.
6. Select the arc and refer to the Entity Info pane for the calculated radius.

Does this work ? Refer to the photo of the mock up attached.
dmccallum attached the following images:
imag1509.jpg imag1508.jpg capture4.jpg capture3.jpg capture2_10.jpg capture1_3.jpg
 
dmccallum
What I figure my final vane cut patterns will be. Calculating the radius for the inside and outside edges of each of the interior and exterior vane sets is completely overkill. Simply using the drum facing calculated radius for the inner vane edges would have been adequate. But then it's simple enough with the method above.
dmccallum attached the following image:
capture5.jpg

Edited by dmccallum on 11/07/2016 05:51
 
dmccallum
I've shared my initial 2D drawings at https://dl.dropbo...r%202D.zip

The zip contains SolidEdge 2D Drafting ST9 files for parts to be laser cut and those to be fabricated. I'll export to DWG some time soon but Solid Edge 2D is free.

It's mostly there and I'll up date the zip as I finish it.

Welcome any feedback.
Edited by dmccallum on 11/17/2016 08:45
 
dmccallum
Should mention that I've only included the roast chamber and cyclone at this stage as I'm having 2nd thoughts about the cooling tray.

I'd originally thought a traditional round tray with agitator arms but I'm not convinced this is entirely necessary for a 0.5-2Kg machine. As nice as it'd look be quite a bit of additional fabrication.
Any steer on this from anyone ?
dmccallum attached the following images:
capture33.jpg capture32.jpg
 
allenb
As long as you're able to draw a proper volume of air across the total surface area of an adequately sized cooling tray, there's no need for stirring arms for a 2kg batch of coffee. Go round or square. Round will give a more traditional appearance.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
AnthonyD
For my cooling tray I used a cheap stainless pot cut to height and holes drilled in the bottom. No agitator, I just stir with a wooden spoon. I'm using mini vac motor but it tends to overheat.
 
broeker
Some great work happening here 😊
 
dmccallum
Moving things on slowly, I've had some of my parts cut. I'm always impressed with the accuracy. The hopper gate valve has come together just as I'd imagined.

Next, I need to get to grips with my new TIG welder...
dmccallum attached the following images:
imag2120.jpg imag2119.jpg imag2118.jpg
x1
 
eschlukebir
very nice. This thing is going to look great. I'm slowly hacking mine together, and its going to be nothing like this. Great work!
 
allenb
I agree. I love seeing parts come off the fabrication bench from those who are fortunate enough to be able to produce high precision and slick aesthetics with their builds. Can't wait to see this one in a video roasting some great coffee!

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
dmccallum
Have moved my file store. If anyone wishes to view my 2D drafting and cutting files you can find them here,

https://drive.goo...sp=sharing

3D Sketchup file is at https://3dwarehou...r-2Kg-Drum.
 
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