How I aligned my Rancilio Rocky.

Grinders are one of the keys to exceptional espresso. Discuss them here.
coffinnate

#1: Post by coffinnate » Feb 14, 2016, 3:33 pm

A few months ago I was going to replace the burrs on my Rocky. I took the grinder to my shop, and decided that it would be fun to measure alignment before and after the replacement. Everything I measured was very close to perfect, always <0.001". Then I checked the parallelism of the axis of the burrs and the axis of the motor shaft (which the lower burr carrier is mounted on) and found a major problem: they were so badly misaligned that if one edge of the top burr just touched the bottom burr, the diametrically opposed edge was around 0.006" away. I finally found that the problem was that the grinding chamber was not sitting straight on the motor housing. This pictures show the grinding chamber on the left, pulled onto the housing by the long screws.
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The housing is made of rolled and welded steel, with the weld showing at the front in the attached image. If you look closely at the right edge of the weld, it is apparent that the housing was not aligned well. The same error existed at the top edge, which is the alignment surface for the grinding chamber. In the next image (the top of the housing) you can see the step at the bottom of the image, and can see the areas that contacted the chamber.
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I cut the alignment surface of the housing ~75% flat on a vertical mill, then reassembled, shimmed until I had excellent alignment, and then recut the surface to match the shims.
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I think I ended up taking about 0.014" off the high point. It was fairly tedious. After reassembly I had excellent alignment, other than the thread slop. I ended up making a locking ring (next pic, big brass circle) to go on the upper carrier. I can tighten it against the top edge of the grinding chamber, locking everything in place.
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The ring is thick enough that I can't screw the upper carrier down as far as was needed, so I made an extension (aluminum part next to the burr), which I sized to run within about 0.002" of the chamber, to keep grounds out. When assembled the greatest combined error I measured was less than 0.001". I added a little knob that sticks out the ventilation slot on the right, to tighten the locking ring, and a spring (hooked around the nail visible where the adjustment lock used to be) pulling the knob forward to keep it locked.
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So far, I'm very happy with the mods, I'm clearly getting much better and more consistent drinks, and can make very good ristrettos now, which I couldn't before. I'll use a while more as is, then if I can't think of more mods I'll finish the cosmetic stuff.

earlgrey_44

#2: Post by earlgrey_44 » Feb 14, 2016, 4:17 pm

Wow, a lot of beautifully done work.

I take satisfaction in fixing something that was broken/sub par and getting it up to it's full potential, I'm betting you feel the same.

There's a lot of over the top dismissal of the rocky to be found, but it can certainly make world class shots - especially yours! :)
Trust your taste. Don't trust your perception.

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dsc

#3: Post by dsc » Feb 14, 2016, 9:20 pm

Such a shame that the grinder was so badly misaligned even though the parts which make it are not that bad to begin with. Curious how much work / time / money it would add to the overall numbers if they decided to alter their manufacturing process and machine the mating surface of the body?

This also takes me back to something often ignored when talking about re-alignment, assuming that everything apart from the burrs on the grinder is well aligned and simply blindly re-aligning against parts on the grinder for example the burr-mount. If this Rocky was to be re-aligned as most people suggest ie. use shims to center the burrs in the mounting parts, it would still be way off. Having a gap of 0.006" / ~0.15mm when one side of the burr is touching must have a detrimental effect on the grind quality, glad to hear it's all much better now and thanks for sharing the info / photos.

T.

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nickw

#4: Post by nickw » Feb 15, 2016, 2:34 pm

.15mm out is terrible!
If you're within .025mm how you're doing good.
If you can get it down to .01 axially, you'll probably notice a benefit again.
Enjoy the results :)

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AssafL

#5: Post by AssafL » Feb 15, 2016, 2:43 pm

Someone ought to teach grinder makers to use a refractometer.
Scraping away (slowly) at the tyranny of biases and dogma.

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nickw

#6: Post by nickw » Feb 15, 2016, 2:44 pm

dsc wrote:Such a shame that the grinder was so badly misaligned even though the parts which make it are not that bad to begin with. Curious how much work / time / money it would add to the overall numbers if they decided to alter their manufacturing process and machine the mating surface of the body?

This also takes me back to something often ignored when talking about re-alignment, assuming that everything apart from the burrs on the grinder is well aligned and simply blindly re-aligning against parts on the grinder for example the burr-mount. If this Rocky was to be re-aligned as most people suggest ie. use shims to center the burrs in the mounting parts, it would still be way off. Having a gap of 0.006" / ~0.15mm when one side of the burr is touching must have a detrimental effect on the grind quality, glad to hear it's all much better now and thanks for sharing the info / photos.

T.
Ditto, most are terrible.

I also wish manufactures would spend more time/money where it matters: alignment. Although that's another story... as users would complain the grinder is less forgiving.

Re shims (and please don't get the wrong idea about me here):
While I recommend people shim their burrs when installing (easiest way for the average person to get decent results) one must fix underlying alignment problems first. No arguments there. That's the most important, and that's where the majority of the problems lay. I've stated that on BaristaHustle before with people ask about alignment. Please don't get the wrong idea about me here.

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dsc

#7: Post by dsc » Feb 15, 2016, 3:43 pm

I wasn't picking on anyway specific Nick, just pointing out something which might not be known to some / most. The issue with alignment is that it can be sometimes easily fixed (like shown above) but you need to have the right tools and know what you are doing. You can only go as low with errors as possible and in most cases shims are the only available solution.

Regards,
T.

day

#8: Post by day » Feb 15, 2016, 3:59 pm

Hmm I don't really understand how to but I imagine I need to do something to improve my mdf...this looks great but I am pretty much lost.
Yes, i you per this on an iPhone

jwCrema

#9: Post by jwCrema » Feb 15, 2016, 6:13 pm

I can't imagine how many Rocky's are tossed or in permanent [deep] storage due to this problem. Had this solution been identified a decade ago there would have been an impact on the grinder industry and market share might not be the same as it is today. Well done!

coffinnate

#10: Post by coffinnate » Feb 15, 2016, 8:56 pm

Thanks for all the replies.

It's kind of weird that most of the parts of the grinder were made very well, but the motor body had a glaring misalignment and the threads are very sloppy. I don't have any idea if there are many other Rockys that have the problem with the motor, but from what I've read most have loose threads. The motor body problem seems like something that would be trivially easy to fix at the factory, simply by visually checking alignment before welding.

I think the problem with the motor body could have been addressed by shimming between the body and the grinding chamber. If I didn't have all the machine equipment I would have tried that as a permanent repair. The difficult part, assuming you have a good depth micrometer, is the tedium of measuring alignment, shimming, measuring, and repeating until it is good.

I'm not sure how well the teflon tape mod fixes the sloppy threads. I'm sure it would improve things, but haven't tried it. The locking ring works well, but is not as easy to adjust as I would like.

I wonder if the short burr life that Rocky's seem to have is due to the burrs being crooked, and the fixed burr getting rapidly worn on the side with the largest gap for the grounds to escape. If this is were the case, remounting the top burr a third turn off would improve grinding. Has anyone tried this?

As far as getting the side-to-side gap variation under 0.01mm, I could well be there, but am approaching the limit of what I can measure easily. My current approach is to measure the distance from a reference flat I cut on top of the top burr carrier to the locking ring I made, which sits on the top of the grinding chamber. I've measured the parallelism of the reference flat and tho top burr, the sides of the locking rings, and the top of the chamber to the bottom burr. Worst case stack I can find at outer burr diameter is less than 0.001", typical is around 0.0003". In the espresso-grind range it is very small.