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10/21/2021 2:41 AM
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Verified a couple of physics laws
Hamilton
Just in case anyone was wondering, areas of high pressure still move through areas of low pressure. I tried my first test roast with the rob roaster half pound hot air roaster yesterday. I had the heat gun sticking through the side of the aluminum tube perpendicular to the tube. The pressure from the blower basically blew how air from the heat gun backwards through it. After about a minute, smoke started billowing through the back of the heatgun.
Ooops! No test roast this weekend, I guess. I'll be re-assembling the roaster with the heat gun in line with the blower, more similar to Chad's and Roaster Rob's design.
seedlings
I know there are half a dozen guys here with similar intentions. We all groaned just now.

You learn like I learn.

I am curious to know how much coffee the heatgun will roast for you! Keep at it, and thanks for taking one for the team!

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
endlesscycles
half a pound. that's exactly how much.
-Marshall Hance
Asheville, NC
Hamilton
Yes, based on Marshall's input, and your leaf blower roaster, I'm guessing the 1600W heat gun will roast half a pound but each roaster is slightly different. The asymetrical cylinder design is a marvel for bean lofting but I think is inefficient with heat so I will be interested exactly how things work out. I'll certainly post my results
Hamilton
Another frustrating attempt tonight. I tried 7 ounces of beans and I was unable to reach first crack. After 15 minutes I was fighting to get past 225 degrees. I thought I would be able to get through a test roast without any real control over my vacuum motor speed but it seems to be outgunning the heat gun by a pretty wide margin.
John Despres
ShockHey, Hamilton, we need pictures!

Respect the bean.
John Despres
Fresh Roast 8, Gene Cafe, JYTT 1k, Quest M3, Mazzer Mini, Technivorm, various size presses and many more brewers.
endlesscycles
You'll definitely need to have control of your motor, and have tight fittings, and have an insulated roast chamber.
8oz is the upper limit to heat gun air roasting.
-Marshall Hance
Asheville, NC
Hamilton
Picked up a router speed controller today at Harbor Freight.. It works great (the vacuum doesn't scream quite as loud with it, either). Still absolutely no luck though. I didn't get above 375 degrees after about 13 minutes. Better than last time, but still very annoying. I'm also out of green beans to test with now. I'm going to see if some insulation helps, but I'm skeptical that it'll buy me ~125 degrees of efficiency. At this point, if it gets me to where I can roast just 4 ounces at a time, I'll take it.

I have a couple pictures I snapped during the would be roast today, although no smoking heat guns or anything like that.

farm3.static.flickr.com/2704/4279969644_ae98258651_m.jpg
Edited by Hamilton on 01/16/2010 3:45 PM
Hamilton
Here is another pic of the motor (now with speed control!) and the heat gun handle.

farm5.static.flickr.com/4034/4279969866_b31f881abf_m.jpg
Edited by Hamilton on 01/16/2010 3:47 PM
Hamilton
Off to sweet maria's!
Edited by Hamilton on 01/16/2010 3:52 PM
endlesscycles
Your diameter is too big to roast 8oz with a heat gun. Try 3" diameter. You are loosing all your heat before it gets to the beans. Put the chamber 2" above the heat gun; if you start the fan first, you won't scorch.

If all else fails, roast 4oz twice.
-Marshall Hance
Asheville, NC
RoasterRob
Marshall is right. 3" pipe should make it work.
My 1st version of this roaster was a 3" ss pipe jammed over a popper element section with a hairdryer preheating the air going in from a light dimmer controlled electrolux (400watt dimmer lasted 20 or 30 roasts). The 3" pipe will help 2 ways. Smaller perf section so lower air volume to keep the beans moving and therefore the air is hotter. Taller bean column so the efficiency is improved. Mine had about 2kw heating and could do 10oz (280gms) anymore and the beans started to get blown out the top. Roast time was about 11 mins, from memory the dryer was on the lower power setting most of the roast time. I still have the RC somewhere.
I posted pics of it on someones website bout 8 years ago.

Rob

back from holiday in the sunny north. work was a shock to the system.
Edited by RoasterRob on 01/16/2010 5:23 PM
VBM Minimax 2gp, 1gp Reneka Techno, 2 gp la Pavoni Pub, la Cimbali M28, SJ Maz, FB 6kg HM roaster and other stuff
Hamilton
Thanks Rob. What is the benefit of having a higher bean column?

I initially went with the 4" pipe because I was worried about being able to spout the beans and I wanted to have flexibility of batch size which seems pretty silly in hindsight. I not only was able to spout the beans, but the colander I put on top of the cylinder to keep the beans from spouting too high actually got blown off of the roaster (along with all the beans) at full power.
The upside of the pipe is that it seems to be sized pretty well for my 'heat gun in the chamber' set up. I will see if I can make the 3" work because that seems like my best bet for making this heat gun work. I think there is just too much aluminum soaking up heat (along with a good bit of airflow).

Good you hear you're back from vacation. Wouldn't want to get too comfortable there.
Edited by Hamilton on 01/19/2010 4:38 PM
RoasterRob
I can't give scientific reasons only empirically based if you can call it that. If the bean bed depth was only 1 or 2 beans deep the air would do very little "work" in heating before being wasted. The taller the column of beans the more beans are in the air flow. For a 3" tube IMO the optimum is between 8 and 10ozs.
Leave your HG in the 4" tube and cut off the tube above the HG. Fit a plate with the perf section suitable for the 3" tube, fit the 3" tube to that.

From alt.coffee way back then. don't know if there is anything usefull in the thread.

http://groups.goo...96a9986ee3


regards

Rob
Edited by RoasterRob on 01/20/2010 3:44 AM
VBM Minimax 2gp, 1gp Reneka Techno, 2 gp la Pavoni Pub, la Cimbali M28, SJ Maz, FB 6kg HM roaster and other stuff
Hamilton
Thanks again Rob. I appreciate the time you've taken to respond. I bought a 4" x 3" duct reducer and a 3" diameter aluminum duct pipe last night. I was planning to attempt exactly what you suggested.

I will post my results this weekend.
RoasterRob
The perf area on my 3" RC has 28 x 3.2mm holes over a "D" shaped area that is 65 x 23mm. Hole size and spacing can make a big difference to how the beans flow JMO.

Rob
VBM Minimax 2gp, 1gp Reneka Techno, 2 gp la Pavoni Pub, la Cimbali M28, SJ Maz, FB 6kg HM roaster and other stuff
Hamilton
I had a bit more luck this weekend. Got 3.8 ounces (3.2 ounces post roast) of beans to about 400 after 6-8 minutes and was up to 450 by the time I cut it off at about 11 minutes. That thing cools really fast too. 450 - 150 in about a minute.

I still need to do a bit of tweaking. I did not drill holes in the entire perforated section which I think led to what looks to me like some extremely uneven roasting. I suspect that the horizontal section of perf plate that wasn't drilled just got super hot and started cooking the beans. Also, I have a larger perforated area than you did Rob. Obviously, a larger section requires more airflow to loft the beans = slower roast times. i will have to see how subsequent roasts are.

Here is a pic of the heat gun portion of the new chamber with the 4x3 duct reducer.

farm3.static.flickr.com/2684/4305757302_efc9234df0_m.jpg
Edited by Hamilton on 01/25/2010 11:27 PM
Hamilton
Here is a picture of the beans. I don't know a lot about roasting but they seem uneven. I was using 2 year old beans from a sweet maria's blend that a friend had sitting around, so I'm not sure if that would cause more unevenness. This was right after cooling, and the color seems to have evened since then.

farm5.static.flickr.com/4027/4305013117_bbfd61eafe_m.jpg
Edited by Hamilton on 01/25/2010 11:29 PM
John Despres
Do you know what kind of beans they are? There could be a non-roast reason they're uneven.

John
Respect the bean.
John Despres
Fresh Roast 8, Gene Cafe, JYTT 1k, Quest M3, Mazzer Mini, Technivorm, various size presses and many more brewers.
Hamilton
It was the Sweet Maria's Puro Scuro blend, which I guess is Ethiopia and Sumatra.

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