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