454Casull Senior Member Joined: 13 Jun 2011 Posts: 1 Location: Toronto, ON Expertise: I like coffee
Posted Mon Jun 13, 2011, 4:43pm Subject: Re: Hario Mini Mill Slim
I picked up a Slim (Thanks Bendy!) and took it apart and started drafting some of it. Making an insert will be somewhat difficult (not impossible), as you'll soon see.
I don't have my modeling software on this PC but anyway, for my mill:
- outer diameter varies between 40.12 mm and 39.85 mm on the side with the fine serrations. I believe the nominal OD to be 40mm. - outer diameter varies between 40.19 mm and 40.43 mm on the side with the coarse (cracking) serrations. One might think that there is a taper, but I think the variation between each end is due to the casting process. Checked with a straightedge, the narrowest diameter is invariably in the middle, exhibiting an hourglass-like shape.
Anyway, the way this piece is, it would be fairly simple to "expand" the OD to match the plastic seat in the bell housing.
- inner diameter varies from 9.96 mm on the narrow end to 11.84 mm on the wide end. By eye (using a shaft held tight against the wall), it looks to be a linear taper. - keying the drive shaft to the cone is a fairly straightforward affair for whatever solution you use - keeping the step function of the tri-lug (trying to avoid the use of "tri-wing") nut is a little more difficult.
There are several points of interest, some of which are...
- burr sleeve seat: -- the seat inner diameter (ID) measures between 41.98 mm and 42.05 mm on mine. By all (simple) tests it looks as though there is no taper in the seat, meaning that the sleeve drops into a cylindrical bore. Thank God for that. Caution! The "real" ID is slightly smaller due to the presence of the 4 ridges aligned with each of the cardinal keys. If your model is well-used, these ridges may disappear due to wear, and if so, will serve to add slop over time.* If you use a soft medium to fill in the concentric gap (tape of some sort), these ridges may just cut in and be OK as they are... or they may make it impossible for the tape to stay on the sleeve as you slide it in. A rigid spacer (brass or stainless steel) may work better with the presence of these ridges. -- the seat depth - irrelevant at this point - drive shaft bushing: -- ID measures out to be approx 6.15 mm at the top, meaning a little over .15mm of slop just at the one end. - drive shaft lower bearing insert: -- ID measures out between 6.10 mm and 6.15 mm. Same as the other end... but still slop. Even if the center burr were perfectly centered on the shaft (and we haven't done that yet), its circular runout would be up to 0.6 mm (ask for math).
Drive shaft: - appears to be 6 mm round bar material. Tolerance is not tight - 0.05 mm undersize on mine. The thread looks to be M6x1.0, but I will need to double-check that with a nut. - 5-point male drive circumscribes approx 6.70 mm and inscribes approx 6.15 mm. - a drill with a 1/2" chuck would be able to grip the lip underneath.
a poster above has noted that the plastic catch cup locks the sleeve in place when screwed in. This is true and would eliminate wear on the 4 ridges. However, this cup does NOT locate or center the sleeve, only keep it from moving.
1) For the slop between the drive shaft and the bushing and spacer, the good solution is to tape the shaft with a durable material, as an above poster has done. The better solution is to JB Weld the bearing surfaces to build them up and then turn down the ODs on a lathe to match your particular sizes. The perfect solution is to machine a custom shaft from stainless steel. 2) For the slop between the sleeve and the seat, the good solution is to tape the sleeve. The better solution is to machine a spacer (can be cut down from a 40mm sleeve bearing, but be sure to select a brass that doesn't contain lead). Don't know a perfect solution yet. 3) For the accumulated slop between the drive shaft and the center burr...
Posted Sat Aug 27, 2011, 5:29am Subject: Re: Hario Mini Mill Slim
How consistent is your modified HMMS compaired to a skerton or CM-50? I'm asking because even though I'm currently on an obsession-driven journey to save up for a "Rocky-class" electric grinder (which is probably gonna take me half a year or more), I'm still up for a sideline switch to a HMMS/CM-45 if it can do a noticeably better grind than my currently owned and modified CM-50.
The thing is, even with both upper and lower body stability mods, I found that there are still about 40% of total bean grams that are coming out as dust (and by 'dust' I mean exactly what you said before which are particles that are just way smaller than others).
So what about your grinder? You think you're getting a significantly lesser dust count than mine when you're grinding for drip or press pot? Because if you are, then I''ll immediately get one the very second I find a store that sells it.
Posted Mon Aug 29, 2011, 5:14am Subject: Re: Hario Mini Mill Slim
Problem is I have no idea how this compares to a Kyocera CM-50 or Skerton.
Well....let's just say that your post has totally convinced me to buy an HMMS (or a CM-45) as soon as the opportunity arrives. You are right about the Skerton being bad news. It is just poorly designed overall. Aside from the severe lack of stability, the manufacturers also made the terrible mistake of using a very weak threaded metal as support for the hand crank. The only positive thing I can probably say about it is that the outer burrs are very snug unlike what you described about the HMMS.
Just to add another thought:
I'm pretty curious about the CM-45. Orphanespresso really praised it a lot and I'm assuming that what they reviewed was straight out of the box. It's a shame I currently don't have access to both HMMS and the CM-45. I'd really like to make a side-by-side comparison of the two.
santunoo Senior Member Joined: 5 Mar 2008 Posts: 63 Location: Hong Kong and Ithaca, NY Expertise: I love coffee
Grinder: Anfim Milano and Hario Mini... Vac Pot: Hario TCA-2 Drip: Nel-Drip
Posted Sun Sep 11, 2011, 6:42am Subject: Re: Hario Mini Mill Slim
And I discovered something this weekend.
I noticed the inconsistent size and watched the grinding on setting 12. The inner cone of the grinder was visibly eccentric with just a little bit of sideload. You could almost see the large grind chunks pop out of the large clearance area and the powder come out of the tight side.
After staring at it a bit, moving parts, and then full disassembly, I noticed a few things.
-During operation, the central drive shaft has a significant amount of slop. I could wiggle the shaft and watch the center cone move around.
Upon disassembly: -there are two bushing/bearings on either end of the central drive shaft. These are not very tight to the shaft, but are definitely intended to hold the shaft in place during grinding. -The center cone has a locked key plastic insert, but the ceramic center cone can move around a bit. -The outer part of the ceramic grinding surface is keyed to the housing, but also has some slop. It is locked in place when the receiver is attached.
The top has a very good fit to the center shaft sleeve, it is obviously intended to support the crank end of the sleeve during grinding.
I went to the two bushing/bearings on the shaft, marked where they were, then added tape around the shaft to make this a very tight fit on both ends.
Upon reassembly, the center shaft was VERY stable. Surprisingly, still very little resistance, even though the bushing/bearings were fairly tight.
I set the grinder to 12 clicks, then pushed the cone back several times to "center" the outer part of the burr, then careful not to disturb the outer part, screwed on the receiver.
Ground 15 grams of beans for coffee - the grounds were remarkably consistent, with probably 60% less dust. The puck usually comes out after brewing in two parts (brewing inverted Aeropress) - the "boulders" settle against the plunger, the dust ends up against the filter. Previous to these mods, the puck would be about 1/4 "fine packed sludge" against the filter and boulders against the plunger, and would frequently come out of the Aeropress in a dual layer puck.
Now, the puck ends up with a very small layer of sludge fines on the filter, probably less than 2mm thick, then the remaining puck is made up of classic Press Pot grounds. Consistency under magnification is awesome.
Note that this requires removing the central shaft - this is not typically part of disassembly.
You, sir, are brilliant! I followed your directions, and for the first time in 2 years of using the Mini Mill, I get a cup of coffee that closely resembles what I get when I grind with my Anfim or Baratza. Not only that, but when I use a V60, for example, the wet grinds settle evenly in a conical shape whereas before they would settle flatly due to the inconsistency in grind size (the small particles would settle at the bottom with the bigger pieces resting on top). The same with the Aeropress. Now the puck is almost even whereas previously it would be half fines and half course particles.
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