Monolith Flat SSP burr upgrade: installation, alignment and performance

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#1: Post by Peppersass »

This is a fork of the Monolith Flat with SSP? thread. That thread is mainly about the announcement and availability of the SSP burr upgrade, with a little talk about tools required, some fitment issues with early Flats, etc. I thought it would be a good idea to have a thread dedicated to installing the burrs, checking alignment and evaluating initial and long-term performance. I'll do this in three separate posts: Installation, Alignment and Performance. This one covers Installation.

I should mention that my Flat is from the first (or maybe second?) production run, so it has the original Mythos burrs. Denis later switched to a slightly different set of burrs that he felt were a little better. I opted for the SSP burrs because, evidently, there's more of a qualitative difference from the Mythos burrs than the later burrs (which is not to say that there's no difference from the later burrs, just more of a difference from the original Mythos burrs.)

Before changing the burrs, I pulled a couple of shots of one of my go-to coffees with the old burrs and recorded the whole bean weight, ground weight (dose), grind setting, grind time, beverage weight, shot time, %TDS and extraction yield percentage (the last two measured with a VST Lab III refractometer and CoffeeTools.) This established a base line for comparison.

I also checked the alignment of the original Mythos burrs before removing them (well, I tried but wasn't successful.) More on that in the Alignment post.


I don't have any actual photos of the installation process, but I've included some photos of the grinder and burr chamber taken at an earlier date. The installation process is pretty straightforward and the Flat's design is so elegant and simple that most owners won't have difficulty learning how to do it from the manual and the text below.

The SSP burrs are marked Top and Bottom on the reverse side, but it appears to me that either would work in either position because the cutting edges face the correct direction either way. The top and bottom burr patterns are almost identical, but have what appear to be very minor differences. Just in case, I installed the burrs as indicated.

Before starting, gather the tools you'll need:

1. A 3/16" Allen (hex) wrench for removing the top plate.
2. A torque wrench or screwdriver capable of producing 3Nm of torque.
3. A 2.5 mm hex bit for the wrench or screwdriver.
4. A small, flat blade screwdriver.
5. Toothpicks, dental pick and/or paper clip (see text below).
6. Small brushes.
7. 99% Isopropyl alcohol or equivalent reside-less cleaner
8. Paper towels.
9. Shop vac or vacuum cleaner.
10. Wet erasable marker (if checking alignment.)

I used this torque screwdriver with this bit set. I selected high-quality tools to minimize the chances of stripping the screw heads, incorrectly torquing the screws, etc. I have other uses for these tools, and I'm a bit of a tool collector/nut anyway. That said, Denis says the torque setting isn't critical, but should be equal for all three screws. You may not need as high-quality a torque tool, but I'd advise getting at least a good-quality 2.5mm bit.

The procedure for changing burrs is documented in the Monolith Flat manual, though there's not much to it. All you have to do is remove the two large hex bolts at the top of the (red or black) top plate, and lift the plate off. In this photo of the top plate you can see one of the two bolts at the top right corner of the red top plate:

In some cases, the sidearms may hold the top plate tightly, so it may be necessary to loosen the top bolts of one or both sidearms. That was necessary the first time I removed the top plate, but hasn't been necessary since.

Once you remove the top plate, you'll see the burrs. Here are the bottom burrs (Mythos burrs shown):

And the top burrs (Mythos burrs shown):

You must thoroughly clean the 2.5mm hex holes in each of the six screws that secure the burrs. Denis stressed this to me several times, and I can't emphasize it enough. You must clean every spec of coffee grounds out of the holes until you see nothing but shiny metal. If you don't do this, there's a chance the 2.5mm bit won't go deep enough into the hole and will slip and strip the screw heads. It's well worth taking your time to clean the screw holes so this doesn't happen.

In my case, the burrs had never been changed in the more than 18 months since I bought my Flat, so coffee was packed very tightly into the screw holes. It took quite a bit of time and careful effort to get it all out. I don't think it could have been done with a toothpick. The job required a metal tool -- a dental pick or a paper clip. I used a dental pick from this set. I've found many uses for them.

After I removed the screws from the bottom burr, I wasn't able to lift it out of the burr carrier. It seemed to be a pretty tight fit. I was eventually able to rotate the burr, but still couldn't lift it out. The burr was lying perfectly flat in the carrier, so I wasn't able to slip the point of one of the dental picks under the edge to pry it up. That's when I realized that if I removed the magnetic chute, the edge of the burr would be exposed through the hole in the burr chamber:

All I had to do was insert a small flat-blade screw driver into the hole and slip the blade under the edge of the burr. A little gently twisting and lifting popped the burr loose of the carrier.

Then I used the shop vac, brushes and paper towels soaked with 99% isopropyl alcohol to thoroughly cleaned the burr chamber, removing every spec of coffee grounds and coffee oil. This is a crucial step to ensure that the new burr lies flat in the burr carrier.

At this point, I decided to check the fit of the bottom burr before removing the top burr and cleaning its mount. That's because, as described in the Monolith Flat with SSP? thread, RyanJ found that the SSP burrs didn't quite fit in the burr carrier of his Flat. The fit was so tight that the burr would not lay flat, which is crucial for alignment. RyanJ's grinder was an early production model, and evidently Denis changed the dimensions of the burr carrier in later production runs. There's some question as to whether this was caused by the OD or ID of the burr being a little out of spec for the original burr carrier, but one way or another it was a no-go and the burr carrier would have to be updated with a new burr carrier at the factory in order to install SSP burrs.

It should be noted that, as described in the same thread, another owner of an early Flat, FotonDrv, was able to install the bottom burr so that it laid flat, though the fit was tight.

My grinder being from an early production run, I figured it would be best to check the bottom burr fit before removing the top burr.

To my great relief, the bottom burr fit perfectly. And it wasn't a tight fit. It seemed to fit like a glove, rotating smoothly in the carrier but with no radial play to speak of. I rotated the burr to check the alignment with the screw holes in the burr carrier (there were actually two sets of holes, spaced differently), and selected the set of holes that centered the screw holes best within the burr holes. I tightened each of the three screws a little at a time, moving from one to the other, until they bottomed out. I gave each a little turn to slightly snug them, then torqued each one, in succession, to 3Nm. This is similar to how you would tighten the bolts on an engine cylinder head, gradually tightening each bolt to make sure the piece gets installed completely flat.

Next, I thoroughly cleaned the top burr screw heads, digging out all the coffee grounds with a dental pick, as described earlier. Once the hex holes were clean and shiny, I removed the top burr, cleaned the mount underneath with the shop vac, brushes and isopropyl alcohol, and installed the SSP top burr following the same screw tightening protocol described above.

[Note that after removing the screws of both burrs, I washed all remaining traces of coffee grounds out of the screw heads.]

With the SSP burrs installed, I proceeded to check alignment, which is described in my next post.
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#2: Post by Peppersass (original poster) »

In this post I'll cover how I tried to check the alignment of the original Mythos burrs, why that failed, and my experience testing and adjusting alignment of the new SSP burrs.


For the most part, I followed these excellent pictorial instructions on aligning the burrs in the Mythos grinder.

After removing the top cover (see Installation in my previous post), I marked the edges of each burr with a black wet erasable marker and reassembled the top cover, fully tightening the bolts. Then I turned on the grinder, loosened the lock screw, and slowly moved the grind setting to the fine side until I could hear the burrs just touching. Then I turned off the grinder, tightened the lock, and removed the top cover to see what had happened.

What I found was... nothing. None of the black ink was taken off. Only a very thin line around the very outer edge of the bottom burr had been cleaned of ink evenly all the way around. I concluded that the flat 1/8" triangles around the edges of the burrs didn't touch because the edge at the extreme circumference is slightly raised above them.

Supporting that theory is this post from our member ira, who had a similar experience when he tried to check the alignment of the burrs in his Monolith Flat (don't know whether he had the Mythos or later burrs.)

In retrospect, however, I think I may not have moved the grind adjustment fine enough to bring the flat triangles together. Maybe ira did this too. I may have been too cautious, being concerned about damaging the burrs (after all, if the SSP burrs didn't fit, I needed to go back to the Mythos burrs.) Unfortunately, I didn't realize this until after I had experimented at length with the SSP burr alignment, and by then it was too late to go back to the Mythos burrs. So I don't really know how well aligned they were.

After installing the SSP burrs, I tried to check the alignment again. This time, however, the test worked as described in the article cited above. In was removed from the flat triangles. The bottom burr alignment was darned near perfect, with all the ink gone from the triangles pretty evenly all the way around the burr. The bottom burr looked similar, except for one area along about 25% of the burr circumference where the ink remained.

Following the instructions in the article, I used about a half-inch of metal tape to shim up the center of the "low" 25%. The tape is 3M conductive tape I got at Radio Shack years ago .I measured its thickness at about 0.02mm uncompressed, which was considerably thinner than the only other metal tape I had on hand, aluminum duct tape, which was about 0.11 mm thick.

Good thing, because even that very thin shim had a significant effect. After remarking the burr and rerunning the test, I found it raised the 25% low area enough to wipe it clean. In fact, installing that first shim changed the grind setting where the burrs touched by at least one full number. I think that's an indication of how fine the grind setting resolution on the Flat is -- at least 0.02mm per number.

However, while the 25% area was fixed, another area about half that size showed up as too low. I shimmed it, which fixed that area but produced another low area. I could see that this was turning into Whack-a-Mole, and it might be next to impossible to shim the burr perfectly.

At about this time I realized my testing hadn't been valid because I wasn't tightening the grind setting lock after finding the point where the burrs touched. I tried doing that and found that the burrs no longer touched. Obviously, the lock changes the distance between the burrs, and quite probably the alignment. With some fiddling I was able to find the first setting at which locking the burrs causes them to still touch. While this would seem to be a more valid configuration for a test, it's clear that you have to make the burrs touch without the lock engaged, then advance to a finer setting where they still touch with the lock engaged.

That's a problem. If you have to tighten the setting too much to find the setting where the burrs just touch with the lock engage, then the burrs might touch all the way around because they've been brought too close to each other (i.e., well past the "first touch" setting.)

To explore this, I experimented a bit with moving the grind adjustment past the point of just touching, and got this result on the top burr:

As you can see, the ink is pretty-much removed all the way around, indicating the burrs setting has been tightened too much.

Luckily, I found that I didn't have to move the burrs to this extreme setting in order to find the place where the burrs touched with the lock engaged. Here's what I got for alignment:

This time, the "low" portion of the burr on the right still has ink on it, indicating that the burrs haven't been brought too close together.

I'm still a little uncertain whether the procedure I chose is valid, but I did the best I could. One good thing was that regardless of whether I tested alignment with or without the lock engaged, and regardless of the grind setting I used, the bottom burr always showed as perfectly aligned, with the ink rubbed off quite evenly around the circumference of the burr.

After locking the grind setting, I found that the shims I previously installed on the top burr didn't work the same, so I had to remove them and start over. On the first try with the lock engaged, I found that about half the circumference of the top burr was too low. But before installing a shim in the center of that area, on a whim I tried rotating the burr one screw hole over. When I repeated the alignment test with the lock engaged, the ink was worn off pretty evenly all the way around. Only a couple of places with maybe three triangles each had ink left on them. Close enough.

At that point I declared the top and bottom burrs aligned, thoroughly cleaned both with isopropyl alcohol, and buttoned up the grinder. I'm quite confident that the alignment is as good as I can get it, and very likely not an issue for grind quality. A lot of that has to do with Denis's great design.
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#3: Post by ira »

The way the grinder is designed, the bottom burr should be perfectly aligned which is what you're seeing. The top burr should be close but the threads and the way they lock means the alignment and adjustment will move a bit when you tighten or loosen the lock. Makes it really hard to check alignment with a pen. Probably the best way is to find a suitable setting, lock the top burr in place and don't change the adjustment until you're finished.

I'm sure I adjusted it tight enough, I was not timid as I'm pretty sure you can't hurt burrs doing that.

And on another topic, I'm sure all the other grinder manufacturers use slot screws to hold their burrs because they are easy to clean.

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#4: Post by Peppersass (original poster) »

In this post I'll cover my observations on performance of the new SSP burrs. I expect to add to this post as I evaluate performance over time. In my experience, opinions formed over a lengthy period of time seem to be more valid than measurements, blind tests and impressions formed during the early stages after an upgrade.

In particular, I'll be updating this post after I break in the SSP burrs with about 10 lbs of stale and cheap beans that I have on hand expressly for that purpose.


In the following tests, %TDS and extraction yield percentage were measured/calculated with a VST Lab III refractometer and CoffeeTools.

As mentioned in the first post, I ran a couple of baseline shots on the Mythos burrs to compare with shots pulled on the SSP burrs. I used Dharma Blend from Temple Coffee Roasters, a light-medium roasted blend that I drink regularly. This particular batch is a bit lighter than usual, probably around 110+ on the Tonino scale. As such, it's a little harder to extract than the typical Dharma Blend I get.

I pulled two shots of the Dharma Blend on the Mythos burrs:

[EDIT: You'll have to widen the window or scroll right to see all the columns (last is %EY)]

The first shot tasted a bit under-extracted, so I boosted the temp to 203F from 200F and pulled a little Lungo. Oddly, that didn't change the %EY and the second shot still tasted a little under-extracted. I took this as a sign that, as a light roast it may not have been fully developed and maybe 18.86% was all I could get out of the bean without resorting to a "Slayer-like" shot (i.e., long, slow preinfusion.) Or maybe that's all the Mythos burrs could get out of these beans.

I also ran two shots with the SSP burrs. Like FotonDrv, I was blown away by how much quieter the grinder is (completely different sound) and how fluffy the grounds are. But I also noticed that very large chunks came out of the grinder at times, and the ejection of grounds seemed to come in waves or pulses, almost like the grinder was spitting out blobs of grounds. When I used the open-palm method to purge the last of the grinds, quite a bit came out and it took several pats to get it all. While this bears watching as the grinder breaks in, it didn't seem to affect the shot quality at all (see below.)

I forgot to time the grind, but like FotonDrv I think it's at least as long as the Mythos burrs (29s) or maybe longer. Will get a timing tomorrow AM.

In my alignment tests (see previous post) the burrs touched about one number coarser than the Mythos burrs, so I started with a grind setting of 7. The grounds looked so different, so "powdery", that I was concerned I had under-estimated the shift in grind setting and that the shot was going to choke the machine.

But it didn't. The shot ran a little slower than the second Mythos shot, but the grind setting was very close to where I thought it should be. Distribution didn't seem to be a problem, with a reasonably pretty pour from the bottomless PF. Here's the data:

The higher retention jumps out, but I would caution coming to any conclusions on that. My Flat retained more when the Mythos burrs were brand new, too. After break-in with 10 lbs of beans it settled down, eventually reaching 0.1g-0.2g retention after 2-3 of months.I'll l report back if there's any change in retention after I run 10 lbs through the SSP burrs. If they're anything like the Mythos burrs, I expect the retention to improve. I'm also guessing that the grind setting will move about one number finer as well, like the Mythos burrs.

Noting the retention, I opened the burr carrier to inspect what had been retained. There were two clumps of grounds between the sweepers, each about the size of an elongated coffee bean. This suggested that perhaps I'd used a bit too much water for RDT. So I didn't do RDT on the second shot. This time a little less was retained, and when I opened the burr carrier the space between the sweepers was completely clean, but the burrs had considerably more fine material on them. It looked like a fine coating of chaff. I suspect RDT will be the way to go, but maybe with even less water than the Mythos burrs required (which was very little.)

The first shot tasted ashy, so I cut the temp back to 200F. The second shot wasn't ashy. This, and the higher extraction yields, may be a sign that the SSP burrs are producing grounds that extract a little more efficiently.

Note that on the second shot I changed the grind setting to one mark coarser, but the shot ran two seconds longer and had higher %EY (possibly due to the slightly longer shot time.) Seems backwards (i.e., a coarser grind should run faster), but I would also caution about coming to conclusions about this. I recall that before full break-in my Flat was similarly inconsistent.

As for taste, while my impressions are completely subjective, I've been doing quite a bit of cupping over the past few months while I've been learning how to roast. So I'm in the habit of paying a close attention to flavor components, defects, etc. I wouldn't say it was "God Shot vs Sink Shot", but I felt that the SSP shots were brighter, more balanced and had quite a bit more bite on the tip of the tongue, similar to the "pop" I usually get from Slayer-like shots. This could be another indication of more efficient extraction. The shots were definitely not as sour as the shots pulled with the Mythos burrs, which is a good thing. I'm hoping this is for real, but only time will tell.

[Note: I decided to do the initial comparison with espresso only because I didn't feel that I could reproduce pourover cups anywhere near as consistently as I can reproduce espresso shots. I might have been able to do that with my vac pot, but time was too limited for that protocol today.]

EDIT: Performance After 2.5lb Break-in

Yesterday I ground 2.5lb of stale beans leftover from failed roasts. I did it in 60g batches, per a recommendation from Denis when my grinder was new. I have 10lb of beans to use for break-in, but thought it would be interesting to see how the burrs change at the 2.5lb, 5lb, 7.5lb and 10lb marks.

This morning I pulled two shots of Dharma Blend:

(Again, widen the screen or scroll right to see all the columns. %EY is last.)

Several things jump out:

1) The retention has improved to almost nil. Now, the numbers are a little misleading because RDT add 0.1g-0.2g, but that was true of the earlier shots. In any case, it's a definite improvement.

2) The grind setting has moved more than one number in the fine direction (1.4 on the second shot.) That's more than I expected after a relatively small amount of beans for the initial break-in.

3) I didn't record the grind time for the pre-break-in shots, but I'm pretty sure they were close to the Mythos burrs -- on the order of 30s. I did a terrible job with the iPad stopwatch trying to record the grind times on these shots (fumble-fingered it.), but I believe 20s-25s is about right. Definitely faster than before and faster than the Mythos burrs. I'll get better numbers next time.

4) %EY is quite a bit higher than the best I could get from the Mythos burrs (almost 2% for the Lungo shot), and significantly higher than the pre-break-in numbers.

5) As you can see, the shot times are a little shorter for the equivalent brew ratios pulled with the Mythos burrs, so I could have gone a little finer on both shots. Not only does that mean the grind setting has moved even finer than shown, the %EY probably would have been even higher had I ground finer to match the shot times.

That 2.5lb really made a difference!

I'll pull some shots of a different coffee tomorrow, for taste not measurement, then I'll grind the next 2.5lb.

EDIT: Performance After 5.0lb Break-in

Here's the data from two shots of Dharma Blend, the first Normale, the second Lungo:

Retention seems to have stabilized at very minimal. The grind setting has moved finer by at least two minor ticks. The Normale shot has slightly lower %EY than last time, but it also ran faster. Probably means the grind setting has moved three ticks (i.e., should have been pulled at 5.4.) The Lungo shot seems to confirm this, running quite a bit faster than after the first 2.5 lbs. Note the %EY has jumped quite a bit on this shot.

EDIT: Performance After 7.5lb Break-in

Once again, here's the data from two shots of Dharma Blend, the first Normale, the second Lungo:

Retention is still excellent. The grind setting for the Normale shot moved finer by two minor ticks, more than I expected, the grind time is a little faster, and the %EY increased about 1.5%, which is quite a bit. Typically %EY measurements are somewhat scattered, so this may be an outlier. Will check again tomorrow. I didn't match the previous shot time for the Lungo shot. Probably went a little too fine. I would have expected the %EY to be even higher than before this break-in round, but it's lower. Again, it could be an outlier. I'll check a Lungo shot again tomorrow.

I should also note that there's less clumping and pulsing now.

Not quite ready to draw final conclusions, but it looks like the biggest change occurs after the first 2.5 lbs, but there's still movement in the grind setting, grind time and %EY through 7.5 lbs.

Will report back after the last 2.5 lb break-in session.
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#5: Post by FotonDrv »

Nice report on the SSP burrs in the Monolith Fat, you have found basically what I found but did a much better job of documentation and presentation of same. Kudos!

I too have been using zero RDT with the Flat and since I use a wide funnel to catch the grounds that are being spit out the sputtering ejection port that random tossing of the grounds matters not.

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#6: Post by Peppersass (original poster) »

I've edited the third post to add performance results after breaking in the SSP burrs with 2.5lb of beans.

(Posting to that effect because I'm not sure if if edited posts show up as Unread!)

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#7: Post by FotonDrv replying to Peppersass »

I don't think it did show up as unread, but in any case thanks for the update. The burrs are doing what the Mythose burrs did in regards to break-in, i.e. less static.
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#8: Post by TomC »

Great post Dick! It's nice to see some more independent measurements filter in.
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#9: Post by Peppersass (original poster) »

FotonDrv wrote:The burrs are doing what the Mythose burrs did in regards to break-in, i.e. less static.
Yes, I should have mentioned that there appears to be considerably less static. I did mention that before break-in the grounds were coming out in "pulses" or intermittent blobs. There were also quite a few clumps, but they lacked any appreciable cohesion (i.e., fell apart easily), so I didn't mention it. The outer end of the chute accumulated quite a few grinds due to static, too.

Toward the end of the 2.5 lb break-in, I noticed a distinct change -- a more continuous "rain" of fine particles, few-to-no clumps and less static. But this was during the first 3/4 or so of each 60g batch. At the very end there was more static, some pulsing, clumping, grounds clinging to the chute, etc. The latter seemed to be mostly chaff, which typically picks up more static.

After break-in, I did notice a significant lessening of the static symptoms described above, which I believe explains the decreased retention. Not as much pulsing, virtually no clumps, and less comes out when I do the open-palm pat after grinding. Still seeing a bit of chaff clinging to the chute at the end, but that wasn't unusual with the Mythos burrs.

The two coffees I'm pulling have different roast levels, and the symptoms are less with the darker roast. I suspect grind speed might change the equation, too. I'm running at 450 RPM, which was my constant setting with the Mythos burrs. I plan to stick with 450 RPM through the break-in, then experiment with lower and higher speeds.

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#10: Post by Peppersass (original poster) »

I've edited the third post to add performance results after breaking in the SSP burrs with the second 2.5lb of beans (5.0 lbs total.)