From Jeff: Annoyances...The shower screen has a protruding screw head...I found that I had to down-dose baskets 1-3 g compared to my other machine to keep reasonable clearance.

I have to down-dose at least 2g as well to avoid imprint in the dry puck. Even then, I still get an imprint from the screw head in the wet/expended puck. For example, here's an expended 15g puck in a 17g basket, even using the convex tamper:



Would this cause channeling as well? On the one hand, it makes sense that any divot in the bed can be a weak point. But on the other hand, there is no flow coming out of the center of the screen occupied by the screw, so I wasn't sure it would. Thanks.

It also occurred to me, perhaps that's the reason LM provides a convex tamper. To displace the volume of coffee in the puck so the center is slightly lower for more clearance for the screw. (Not sure if someone has already proposed this.)

PaulTheRoaster wrote:I was thinking of convection from the disc but you're right. It seems like my bayonet ring and pf don't get that hot compared to my previous machines but I don't have any data.

My portafilter is hot enough to burn me in the mornings if I'm not careful prepping the puck. Maybe not full boiler temp though.

baldheadracing wrote:
I do not know what LM was thinking, but to me the biggest reason to use a convex tamper is that extraction is less sensitive to convex tamps that are not perfectly level. Even in Italy where every café uses a convex hand tamper, the tampers built into old-school doser grinders - so the tamps are always level - have flat bases.

I was thinking it makes for more consistent extraction. Almost every bottomless extraction you see starts with a ring of espresso around the outside then quickly fills in to the center. Clearly the outside edges are first to saturate and "easiest initial path". A concave puck would compensate for that somewhat, and like you said may be more forgiving. It could also have an effect of "packing the wall" so to speak, when you tamp downward the tamper pressure actually pushes the grounds out toward the edges somewhat rather than straight down. Probably improves the seal along the basket wall.

Regarding the portafilter temperature conversation, I tried to get some FLIR measurements. Almost forgot that reflective surfaces don't show up, so the best I could do was slap a piece of tape on the portafilter and measure the temperature of that. These are somewhere between 15-30 minutes of warming time, I don't know exactly since I was messing with the FLIR cam.

cannonfodder wrote:That photo is deceiving. With an LM spouted portafilter and a 'standard' size demi cup, there is about 1/4 inch clearance FYI. Also as I noted in my writeup, the angled handle hangs down in the way and I smacked it several times with my cup which is why the stock portafilter has a straight handle. But yes, you could do it if you really wanted.

Thank you Dave, that's very helpful.

I have great interest in the Micra and I want to THANK the contribution given by the Team HB for their exceptional reviews of the
Linea Micra.
I find their answers given to support their initial reviews to be honest, straightforward and very helpful.
And even if I not a buyer in the future. I learned a great deal reading their evaluations/comments of the Micra.
I appreciate and now (somewhat) understand the intricacies making espresso and the dedication needed.

Congrats to Team HB:: another_jim, cannonfodder, HB, IamOiman, Jeff and all contributors not mentioned.

baldheadracing wrote:No. A divot in the spent puck is normal and expected on machines that have such screws. The puck can be sucked upwards at the end of the shot by the action of the three-way solenoid, and/or the puck expands once the

Thanks, Craig. That is a huge relief as I was wondering how big I'd have to go on the basket to avoid this wet imprint. My prior machine's screw is flush so it's not something I ever considered.

And while it may not have been the intent, the convex tamper does provide that extra little bit of clearance to help avoid disturbing the dry puck. I did a little "experiment" and I was able to put a full 14g dose of Saka Gran Bar into the 14g basket and not have to dose down.

First with a flat tamper (shows dry imprint).



Then WDT to loosen the grounds, re-level, and apply convex tamper (no dry imprint).