Hi all,

I'm looking for some feedback with regards to the exhaust fan control on the new TJ-067.

To provide a bit of background, I received my machine (a gas version, currently running off of propane) back in January as part of Mill City's "5th Delivery". The exhaust fan on my machine (and presumably on all machines that were part of that and subsequent deliveries) is located on the end of the exhaust pipe. On earlier models, the fan was situated on top of the chaff collector.

Long story short, I'm having a heck of a time taming my fan. Mine turns on at about 45, but can be dialed back to as low as 39 before it disengages. The problem I'm having is that if I bump the fan up to even as low as 42 post onset of first crack, the draw in the drum becomes so strong that it winds up sucking a significant number of beans (I'm estimating around 30 to 60 per 1 KG batch) up into the exhaust pipe. Many ultimately get stuck there, despite efforts to draw them back into the chaff collector by maxing out the fan. This has forced me to resort to removing the fan from the exhaust pipe after every couple of roasts and vacuuming out the pipe. It's a drag and a major time suck.

I've spoken to Steve at Mill City about this, and he suggested that the issue might lie with a bad potentiometer. He's shipped me a new one, and I am considering making the swap. Before I take that step, however, I wanted to reach out and see if anyone else has experienced similar issues with the new exhaust fan setup and, if so, how they've dealt them.

Many thanks in advance!

I have a TJ-066 so I realize that this is not strictly relevant to your model 67, but fan "turns on" at about 30 indicated on the dial, and once in a while I hear a bean getting sucked up into the exhaust. Hopefully the new pot fixes the problem but in the meantime you could try to reduce the airflow through the drum by opening the bean drop door slightly, which will redirect some of the fan's suction. Also might be worth asking the folks at the North Roaster forum.

robmatic wrote:Hopefully the new pot fixes the problem but in the meantime you could try to reduce the airflow through the drum by opening the bean drop door slightly, which will redirect some of the fan's suction. Also might be worth asking the folks at the North Roaster forum.

Thanks Rob. Just discovered the North Roaster forum this morning. Will be sure to inquire there as well. Regards to the bean drop door, that's a good interim idea. I'll give it a shot.

I have an older TJ-67 and never noticed beans in my chaff..
Have you checked your drum speed?

Also is there still a baffle in the drop chute to stop beans from being sucked into the exhaust pipe on charge?

I'm thinking either to much drum rotation speed or you have a bad vane, trapping beans and dropping it in front of the exhaust port..

You can stop your fan and then increase pot to the slowest speed that fan just starts turning RIGHT?

JK wrote:Have you checked your drum speed?

You know Steve from Mill City raised this possibility in a correspondence earlier today. Up to now, on 1 kg charges, I've been setting drum speed to 60 on the dial. I haven't clocked RPMs at that setting though (I will do tonight). Following that feedback from Steve, I did another roast with drum speed at 50 on the dial. I can definitely confirm that fewer beans wound up in the exhaust/chaff collector. That said, I still had the problem, and never pushed my fan beyond 43 (lowest setting is 39). I'll try easing drum speed a bit more on the next roast and report back. In the interim, any particular dial setting/RPMs that you would typically shoot for on a 1 kg charge?

JK wrote:Also is there still a baffle in the drop chute to stop beans from being sucked into the exhaust pipe on charge?

Yes, there is, and it seems well in tact. Audibly speaking, at least, the first indications of "bean sucking" have consistently occurred right after onset of 1C (presumably due to weight loss).

JK wrote:You can stop your fan and then increase pot to the slowest speed that fan just starts turning RIGHT?

Yes, correct. I can.

Thanks for the feedback Johnny!

wrakocy wrote:...on 1 kg charges, I've been setting drum speed to 60 on the dial. I haven't clocked RPMs at that setting though (I will do tonight).

Just to follow up briefly on this, I ran some tests this evening and got the following results:

60 on the dial == 90 RPMs
50 on the dial == 80 RPMs
40 on the dial == 72 RPMs
30 on the dial == 60 RPMs

90 RPMs does seem high....I'll continue to ease off.

Should be in the 50-60 RPM range...
You might need to change the chain drive gear to a smaller one..

JK wrote:Should be in the 50-60 RPM range...

Cheers Johnny. Steve at Mill City confirmed the same offline this morning. Strongly suspect that this is the root problem. Will report back once confirmed, but in the interim, thanks very much for the feedback. Hugely helpful...

wrakocy wrote: I ran some tests this evening and got the following results:

60 on the dial == 90 RPMs
50 on the dial == 80 RPMs
40 on the dial == 72 RPMs
30 on the dial == 60 RPMs
90 RPMs .

. Thanks for sharing this data. I just ran mine with dial on 30 and like you I got 60 rpm, and also like you I have been running at 80+ rpm. An air setting of 25 is the minimum where I can still notice air movement out the exhaust

wrakocy wrote:You know Steve from Mill City raised this possibility in a correspondence earlier today. Up to now, on 1 kg charges, I've been setting drum speed to 60 on the dial. I haven't clocked RPMs at that setting though (I will do tonight). Following that feedback from Steve, I did another roast with drum speed at 50 on the dial. I can definitely confirm that fewer beans wound up in the exhaust/chaff collector. That said, I still had the problem...

Steve and I discussed this today. I avoid suggesting "settings" for drum RPMs. My guess is that you have your drum speed too high, even at 50. Why do I say that?

I have had two different 1Ks on the bench, John Deere and now Baby Blue. On the first, I used 50 as Steve mentioned to you. On the second, I use a somewhat lower setting to achieve the same RPMs. Instead of a setting, get a full capacity charge in there and:

* get out in front of the roaster, a good five feet away. Target an RPM which provides a 45 degree slope/drop/tumble of the beans within the roaster. You should have the slightest bit of congregation of beans at the base of the mass.

That is the approach that Joe Marrocco encouraged me to use and I have found it very helpful. No scorching and sufficient turburlence so that convection heat is shared in the latter part of the roasts. I bump the drum speed at the conclusion of drying phase and again at first crack as coffee swells during the roast.

I attempt to keep that 45 degree angle going throughout the roast without getting anal about it. Hope that helps. If more is needed, call Steve or me at the shop next week. Better yet? Watch the Coffee of the Month video on Wed, 30 Mar, at 3p CST, and send a message to specifically ask a question.