Since you saw the issue, I wanted to mention something I saw posted elsewhere (I think by BDL), but I can't find it. The mention was that if the tamper od is too close to the basket edge, the act of removing the tamper will unseat the puck, causing channeling. You saw this exact effect when you went to the big diameter... so I wanted to make sure it was clear what happened.

Jim

I have found out many moons ago, back when I first started learning this stuff the tamper would suck the puck up and unseat it. My machine came with one of those little plastic things so I made me one, and by shear luck, one the right size, .026" smaller than the basket. Well, I was just learning then and I was getting gully washers for shots. I soon noticed the edge of the puck after tamping was all broken up, so I would go back and tamp it again, just to find it was broken up again when I checked it. Then I tried removing the tamper a lot slower and give it a twist as I withdrew it, amazing the puck was in there nice a tight. I though ok, I tamped again and snatched the tamper out, it completely sucked the puck up and left it sitting at an angle in the basket. Since then, I've always made a slow removal and twisting of the tamper as I withdraw it from the basket.

The oversized tamper for some reason would not put enough pressure on the sides to seat the puck against the sides, it was not me sucking the puck up. I already knew that and was very careful about slowly removing it. Now, I'm anything and everything but an expert in the art of brewing/extracting a shot of espresso, so I guess there was something going on there I don't know, I just found that every time I flipped the basket over, the puck fell out, and never even tried to make and extraction with it. Knew that would have been a wasted effort.

I'm not responsible for the post attributed to me. But what Ben wrote, is my experience as well. As it happens I turn my tampers in a polishing motion (but with more pressure than a mere polishing spin) as a last ditch effort to keep the tamp pressure even across the surface and the surface level. So, I don't have to turn them to break the stiction. Except when I do.

I used to think that tamper shapes didn't make much difference. Then I read a bunch of guys who thought VST baskets needed flat bottom tampers, and I kinda believed them. Then I saw a Heather Perry video where she sort of incidentally in passing said something about preferring C-Flats. And if Heather says it... By the way, she has no memory of me whatsoever. Then I spent a bunch of money on a new grinder, and whenever you spend a bunch of money on something you have to accessorize it, right? So I bought some new tampers -- one a Coffee Concepts Brass Handle C-Flat and the other a Clive Coffee Butterfly.

The Butterfly is a very weird tamper. It has a personality which encourages "consolidation" over "pressing." It also has a (shallow) curve. It's totally changed my tamp style, and I really love the little thing. However, the overweight C-Flat works about as well, and so does my flat-bottomed "eight ball. They're just not as fun.

Odd how a puck made with a 30lb tamp from a heavy as hell tamper has about the same flow rate as one made with a 10lb press from a sylph-like butterfly. Go figure.

As long as it fits.

Rich

I use my the side of my finger when leveling my basket in a circular fashion (similar to Stockfleth's maneuver) only my thumb is at the center to form a concave surface. The resulting distribution corrects the typical advanced release of espresso along the filter edge in flat tamp, such that there is no need for a convex tamper using this leveling method.