Bunnzilla: calibration issue

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mtbizzle

#1: Post by mtbizzle »

I just completed my Bunnzilla (Bunn G series grinder, SSP burrs, sanding alignment of the inner and outer burr housings). I'm having problems with what should be the easy step - calibration.

Calibration is really easy - screw the grind selector plate in, set dial to 0, turn grinder on, turn the grind adjustment screw until you hear burrs chirp. Done. (Video example- http://www.youtube.com/watch?v=oIsvSemiPdQ -- not my grinder but same model )

When I tighten the adjustment screw, it seems to go from no spinning of the burr (auger that the outer burr is attached to is NOT moving/spinning) -- http://www.youtube.com/watch?v=9xcUr3l0ZMI -- to awful grinding sounds -- http://www.youtube.com/watch?v=UWm7HyqbUSE -- you can see fine bits of metal flying around.



A few thoughts --

1. I just did sanding alignment and installed new burrs, maybe the problem could be related to that.

2. The grind selector plate on my Bunn does not sit flat against the frame. I can screw it in, but it's not flush. Not sure if this is new or always like that.

3. The spring in the auger may be bent?? It was stuck in place, rusted when I bought the used Bunn. I had to use oil/force to remove it. It could have bent, and maybe that is causing some alignment issue of the outer burr?

I've spent a lot of time on this project, so I really appreciate any ideas or help :)


(See link below for Bunn's manual for reference and diagrams)
See pg. 18:
https://catalog.bunn.com/public/docs/41 ... 5.0000.pdf

ira
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#2: Post by ira »

I have to say, I'm baffled. Watching you adjust the knob sounds correct. You should loosen the 2 set screws, back off the adjustment screw, set the pointer to the finest setting, tighten the screw till the burrs just touch and then back off till they don't. Then tighten the two set screws to lock the knob to the adjustment screw.

What am I missing?

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mtbizzle (original poster)

#3: Post by mtbizzle (original poster) »

Ah, sorry - misunderstanding. That video is someone else demonstrating calibration on the same model, but it's not mine.

mtbizzle (original poster)

#4: Post by mtbizzle (original poster) »

Trying to trouble shoot this, looking for equipment issues. I'm questioning whether a bushing is missing (#10 in diagram).





Anyone with experience with Bunn G series know if the ring at the end of the shaft (pictured below) is the bushing? Considering buying a new auger spring to see if it helps, as the spring might be slightly bent. Equipment wise I'm not sure what else the issue would be.


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TomC
Team HB

#5: Post by TomC »

It's been a long time since I futzed with my Bunnzilla, but to my recollection, that bronze bushing is soft and easily worn from the previous commercial use (if picked up used), and the spring is also fatigued. If I were to be aiming for the higher level of alignment called for by the sandpaper method to true everything up, I'd also start with a new spring and bronze bushing.

I have all mine new, just sitting in a box, waiting for me to get back to it.

zero610

#6: Post by zero610 »

The bronze part is the bushing. I can't imagine that would seize up enough to completely overpower the motor to stop the burr spinning. Can you turn the shaft by hand? Does the motor spin the shaft when you have the faceplate off and can see the stationary burr?

Probably a dumb question, but when you put the faceplate back on with the new burrs, did you remember to loosen the calibration screw (part of the big grind setting adjustment knob) to a very course setting? The new burrs are a much different thickness than the stock, so if you don't adjust it, the burrs might simply be locked because they're so tight. If not, loosen it very course, put it all back together, then turn to the finest setting and adjust the screw just until burr touch.

When I did mine, it seemed to be very straight forward. Mine was mostly original and I think around 20 years old when I started. Those parts are built like tanks so unless they were really abused, I don't imagine it is anything Bunn related.

mtbizzle (original poster)

#7: Post by mtbizzle (original poster) »

Thanks for your help y'all.
unless they were really abused
It is a used Bunn - worst of it seemed to be, the auger was a bit rusted(?) And the auger spring was stuck. Spring seems slightly bent after oiling it and pulling on it to get it out. Definitely possible it has nothing to do with parts and is user error -regardless I'll plan to buy a new auger spring and bushing.

But, I'm not sure how to remove the bushing to replace it. It seems like it's shoved way back on the motor shaft, I can't seem to get anything under it to move it. Yes, Zero610, I can spin the shaft by hand. The bushing spins with the shaft.
zero610 wrote: Does the motor spin the shaft when you have the faceplate off and can see the stationary burr?
Yes, auger out, motor on, shaft spins.

Looking at the shaft, it does look beat up (look at corners). Maybe the adjustment screw was not nearly loose enough and the shaft was taking all the motor's force..?





zero610 wrote: when you put the faceplate back on with the new burrs, did you remember to loosen the calibration screw (part of the big grind setting adjustment knob) to a very course setting? ..


I did loosen adjustment screw before calibration. Maybe it was not enough. For the calibration screw, I'll loosen as far as it'll go next time I try to calibrate.

Question about loosening/tightening up for calibration.

Maybe there is an issue with the faceplate screws (1&2 in the diagram above). The faceplate doesn't sit flush against the frame. I'm not very confident that these screws are tightened correctly, but not sure what to do other than screw in hand tight.

For screws securing the inner burr to the grinder, and securing the outer burr to the auger, I used a torque screwdriver to 1.2Nm (not tight enough) and then tried to tighten a small amount evenly by hand (? Maybe that's not tight enough).

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zero610

#8: Post by zero610 »

mtbizzle wrote:Thanks for your help y'all.

Maybe there is an issue with the faceplate screws (1&2 in the diagram above). The faceplate doesn't sit flush against the frame. I'm not very confident that these screws are tightened correctly, but not sure what to do other than screw in hand tight.

I don't think the faceplate will sit flush. Here's a picture of mine below.

Maybe also look at your auger and reassembly process and make sure things are going back in the correct order. Follow the Bunn diagram exactly and make sure you aren't missing parts/steps. I don't think the auger or spring would completely stop the grinder motor from spinning the burr.

mtbizzle (original poster)

#9: Post by mtbizzle (original poster) »

zero610 wrote:Follow the Bunn diagram exactly and make sure you aren't missing parts/steps. I don't think the auger or spring would completely stop the grinder motor from spinning the burr.
Agreed, I'm guessing there had to be contact / resistance to stop the auger spinning, or the shear plate wasn't in place.

Just tried to calibrate again. Followed the Bunn manual. Tightened faceplate to hand tight without too much force. Loosened calibration screw as much as possible.



Auger did spin. But the noise was awful and loud. I remember the Bunn being loud, but not like this. It's not a motor hum, over which I'd easily be able to hear the burrs chirp.

No obvious damage to burrs, but there is metal dust in the burr chamber:



There are scratches, I think new, to the wall of the chamber. Maybe it is too loose, and the auger is scratching it?




In any case I ordered a new auger spring and bronze bushing. Anyone know how to fish the bronze bushing out? Any ideas on what to assess to help identify the issue?

leftiesrule

#10: Post by leftiesrule »

I remember having a similar problem after making my Mini-Bunnzilla which included installing the trifecta detent plate. When trying to calibrate and shim the burrs using the marker test, sometimes the motor would hum and nothing would be spinning. There was metal fines in the grind chamber too. I came to the conclusion that the calibration screw was so far out that the burr carrier was wobbling in place and either jamming or dragging on the grind chamber. My problems went away after tightening that calibration screw... I don't use that grinder anymore though but I might just have to since I did end up doing the sandpaper alignment and getting SSP burrs.

On a sidenote that bushing is also installed in the "wrong" direction on mine.

-Adam