I've had some strange run ins with conical burrs for our mazzer roburs lately. We had a timing mod on one robur so we know how long it should take to grind our 21 gram dose - it's about 5.6 sec or so on fresh burrs. I got one set of new burrs from a place down in cali and they >started off< at 7 sec then dulled to almost 10 seconds in one week. I sent them back and the company told me I'd put the burrs in upside down....really? That would be a serious feat if someone could manage to get them in backwards Anyways..
I ordered 2 more from Franke and...same thing! I was working on a different robur at a different cafe (no timer mod) and the new Franke burrs ground a chute-full of coffee in 18 seconds while my old (dull) burrs grind it within about 12 seconds?? (by 'chute-full' I mean if you close the hopper slide and just grind whats in the space between the burrs & slide.)
They are all single phase burrs and the cut on the burrs does seem different but only slightly. I switched them out multiple times to compare and time each set of burrs and also on different grinders. I also marked each set to make sure I remembered which is which. Talk about time-consuming! There's a definite difference.
It's not power because there's a difference between the burrs when I switched them out on the same grinder plugged into the same wall outlet.
I'm taking the sets of burrs I have down to La Marzocco tomorrow to compare them to what they have. The guys said there was a change in production but that was a year+ ago.
This drastic change in speed would be a serious problem for our cafes. If anyone else has experienced this or has any ideas I'd greatly appreciate hearing them.