Throwin' the Chain

Throwin' the Chain

The back end of the roaster doesn't usually get the same amount of attention as the trier, bean temp thermocouples, cooling tray or chaff collector. Chains, belts, sprockets and grease aren't usually featured when we talk about the coffee we drink, or when we write reviews on the coffees we roast. But though they are less discussed, they are equally important parts of the roasting equation. It's annoying when these mechanical parts don't work how they are supposed to, or at all.

Can you relate to the frustration of quickly rigging up a half-assed patch job in order to successfully get through a roasting day? These mechanical failures could negatively affect the roast process in a multitude of ways. For instance, excess buildup on gas burners can restrict gas flow, causing your heat to lag, and ultimately causing you to overcompensate gas or airflow. Or if you don't regularly clean out your stacks, over time, airflow will be restricted causing under developed qualities; or worse, cause a fire. So it is important to look over the often "less checked' mechanicals, in order to avoid an untimely break down. But some of us (me), we have to learn the hard way.

On the L12, the cooling arms are powered by the chains that are driven by the motor. Actually, this single motor is responsible for providing power for the airflow, drum and cooling arms. Over the past several roasting sessions, the cooling fan chain has fallen off during the cooling cycle. Not good. The cooling arms have to be spun by hand when this happens and as you can imagine, it's very hot. I had a feeling that the two sprockets that hold the chain for the cooling arms were not in line with each other.

In the photo below, the chain and two sprockets that are located furthest away from the roaster are the units directly responsible for turning the cooling arms. Not to mention they operate with the longest chain!
The series of chains and one belt.The series of chains and one belt.

The good ol' plumb level is a great way to check the alignment here. If you don't have a plumb level, a piece of string and a small bolt can work fine for this. The alignment doesn't have to be perfect but closer that 2", like mine was. The level was off just enough to throw the chain. It's hard to tell from the angle the photo was taken but I tried to capture the 2" distance that was off.
Hanging the plumb to check the alignment.Hanging the plumb to check the alignment.
Now that we have established the possible issue here, we decided to pull the lower sprocket out a touch to roll a straighter chain line. One set set screw and three bolts had to be removed to release the tension and make room for pulling the flange out a bit. In the picture below, you can see the little bit of distance I can pull the flange out and still feel good about the set screw performing it's job correctly. The three bolts secure the sprocket with large washer rings that you can also see here in the photo below. The sprocket is completely independent of the flange to change speeds if you would like to.
Set screw (black) and three bolts that need to be removed.Set screw (black) and three bolts that need to be removed.
The screws have been removed and now sprocket / washers are easily removed from the flange.The screws have been removed and now sprocket / washers are easily removed from the flange.
I am starting to become pretty good friends with this ball peen hammer. Besides the screwdrivers, it's the tool I have used most for moving things around. A few whacks around this flange and it makes it's way out to the desired distance.
Tap and spin, tap and spin, tap and spin...Tap and spin, tap and spin, tap and spin...
After knocking the flange a little further down the shaft and dropping the plumb level, things are lining up quite a bit nicer. Let's put it all together and see how smooth we run. (Sorry that the video turned out so dark, but you get the idea here)

So far, the chain has not had any issues falling off since the adjustment. These minor adjustments can make a world of difference, and boy it's nice to have one less thing to stress about while roasting!

-Danny Goot



#1 Tension?

Hey Danny,
Loving your articles. I was wondering if you had tested the chain tension at some point? Obviously alignment is key, but we had this issue with an old Diedrich and it turned out that every so often (a year or two in our case) the tension needed to be adjusted in the same way that you would a motorcycle. Don't know if that applies here.

Thanks for always posting good stuff!

#2 Thanks Andrew!

Hey there Andrew,

Sorry for the delayed response.

Thanks for the kind words and I'm glad that the maintenance blogs are helpful for you. I am not familiar with how the chain system works on a Diedrich, but the Probat L-12 I work with does not seem to have an adjustment to tighten the chain. There are a series of chains and a belt that work off of each other. To tighten one, would be to loosen another. The video above gives you a better example than how I could explain it.

Thanks for adding your experience here on the blog forum and it totally applies here. Anything that roasters can add to what I have on these blogs is more than welcome!

Thanks again for your input and comments. :)

-Danny Goot