Cormorant Squeaking and Grinding - Page 2

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
ShotClock (original poster)
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#11: Post by ShotClock (original poster) »

No news yet, I'm afraid. I dabbed a little mineral oil on the faces of the bearings a while ago and that seemed to quiet things down a lot. I haven't roasted on it yet, as i haven't had the opportunity. Will give you an update with how things progress.

It would indeed be nice if they were sealed a bit better than as you describe, but i guess this is a fairly gentle environment in terms of load etc, and sealed bearings with high temp food safe grease might be hard to come by. Maybe other designs would have the bearings away from heat and food, I'd be interested to know, but have no experience with other drum roasters.

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#12: Post by carl_694 »

Did you just use a food safe grease?

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#13: Post by mkane »

500°+ is not a friendly environment.

ShotClock (original poster)
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#14: Post by ShotClock (original poster) »

I used mineral oil on the faces as directed by Johan. I didn't take the bearings apart as Tim mentioned above. I'll be back in touch with Johan if i continue to have problems. He's been extremely helpful, which is even more impressive given that i bought the roaster from a user here, and he has no obligation to me.


#15: Post by Trjelenc »

Another thing I forgot about that has help me with my Huky making an awful grinding at certain temps. I put a small slat of wood, somewhere around 3/8" thick, underneath the base of the stove to angle the roaster backwards a bit. Completely solves the issue, which I think means that the drum slides forward and expands and just rides against the front of the roasted, so angling it back helps keep it off the front face


#16: Post by Milligan »

carl_694 wrote:Did you just use a food safe grease?
Mineral oil is typically food safe. If a grease is needed I use Super Lube. However, Super Lube is rated up to 450F so it may not be optimal for a bearing exposed to direct roast gases.

I had a bit of a grinding noise a few days ago. There are a few interesting things going on during a roast. The drum rotates and pushes the coffee against the face of the roast chamber which puts rearward force on the roast drum. This (you would think) puts axial loading on the bearing. However, the drum shaft is not friction fit to the inner races of the bearings so it can slide back and forth. Nothing stops the the front shaft from moving freely back and forth via the bearing. The rear bearing is similar. So, I was curious to know what stops the shaft from sliding because that interface may cause the grinding noise.

I took the housing off of the drum motor to poke around. The motor works with a worm gear that drives a large toothed gear which is connected to the end of the drum shaft. There is a coupler that the shaft screws into and then a set screw prevents the shaft from unscrewing. Perhaps this is how distance between the drum and the front wall is adjusted.

So, again how is the shaft fixed axially? Well, gears only work when they are fixed in place against all directional forces except the direction of intended rotation. A normal spur gear (with straight cut gears) is primarily fixed perpendicular to the axle. As force is applied to the gears, the shaft/axle experiences a shear force. The bearings carry this force in the direction parallel to their mounting plane. An easy load to carry. Worm gear works a little differently. The worm gear wants to pull away from the motor (or toward depending on the rotational direction) so it experiences its loading force axially along the motor shaft. It transfers this load to a toothed gear. The toothed gear experiences both axial and shear forces. In the Cormorant's case, the axial load on the gear rotation is directed toward the front of the roast chamber. This counteracts the force from the coffee against the front of the drum chamber.

But that is a lot of load to put on a drive right? Perhaps, but the Cormorant has a back up. There is a c-clip around the shaft in front of the gear drive that prevents the coffee from pushing too hard if there is a jam. This protects the drive.

However! I noticed something interesting during operation loaded with coffee. The front shaft appears to move slightly to the rear as expected because the coffee pushes against the front plate but the c-clip at the rear becomes looser as well. So this would mean the front shaft has moved slightly rearward but at the same time the rear shaft moved slightly forward. This is not what I thought would happen. What does this mean? Not sure. I plan to do a full disassembly soon to understand how everything lines up inside the housing and if there is an area that would cause such grinding.

The only thing I could think of is that the drum housing moves slightly under load.

Sorry for the long post and perhaps some of my terminology is incorrect.


#17: Post by Mbb »

I would think you'd be using a high temperature food grade grease in bearings. You can find them easily that go up to 575 f


#18: Post by Milligan »

I wanted to pop back in and say that oiling the bearings fixed my noise. I'm thinking perhaps Johan used a batch of bearings that weren't prelubed. I've been looking into bearings that are fully sealed on the roaster side but open on the exterior side for easier lubrication. The rear bearing is a bit difficult to get to.
ShotClock wrote:I used mineral oil on the faces as directed by Johan. I didn't take the bearings apart as Tim mentioned above. I'll be back in touch with Johan if i continue to have problems. He's been extremely helpful, which is even more impressive given that i bought the roaster from a user here, and he has no obligation to me.
Curious if lubing fixed your issue?

ShotClock (original poster)
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#19: Post by ShotClock (original poster) »

Milligan wrote:Curious if lubing fixed your issue?
Unfortunately, I haven't had the chance to roast yet. Sick kids and work deadlines have had me working through my rather deep bench of George Howell, Manhattan, and Steady State. Hopefully I'll get a little time between Christmas and New Year...


#20: Post by Milligan »

Mine started to squeak again. So badly that it was hard to hear first crack. I had previously checked the front bearing and it was dry so I lubed it. I tried to lube the rear bearing while in place so I didn't have to take apart the roast chamber. That seemed to have cured it for 20 roasts or so. Since that didn't work as a long-term fix, I decided to pull apart the entire thing to find the issue. Luckily, getting to the rear bearing isn't too difficult.

Steps included:
  1. Remove tilt handle with Allen key
  2. Loosen small set screw on the roast drum to motor coupler. Should be an allen key
  3. Remove stainless shell using Allen key around the roast chamber
  4. Slide the inner heat shield out
  5. Unscrew the rear acorn nuts holding the roast chassis together with a 10mm socket
  6. Remove the drum motor cord from the base
  7. Put an old towel under the roast chamber to prevent scratches to the base
  8. While holding the rear motor cage and the roast chamber, gently pull the rear half out. It may need a tap with a rubber mallet to get it moving.
  9. Set the assembly on a towel with the motor cage turned down. Unscrew the roast chamber from the rear motor coupler.
  10. The front and rear bearings are now both accessible. Slide them off.
This takes about 5 mins going slowly, so not too bad. Here are my bearings after around 80 roasts:

The front bearing that I oiled was dry again but still turned. The rear bearing was seized. So, the squeaking came from the bearing turning within its seat. Luckily some of the oil lubed the seat so it didn't do any damage.

I'm guessing either the oil used evaporated very quickly due to heat or they were never oiled. The machine likely has around 20 hours of roast time on it, which doesn't seem like bearings should be worn by then. The bearings are 608z model. I ordered a 10 pack and will try to pack them with super grease in the hopes that it holds up better than just oil. If it is an issue again, I'll turn to Grainger to try to find some specialty bearings in the same size. These bearings are mainly used for skateboards, so I'm somewhat concerned that they aren't up to the task of heat, chaff, and coffee oils.