I got a few pours out of the k10... boy do I love the taste of this grinder! Definitely different from my mazzer SJ (with SSP burrs). The SJ has more top citrusy flavors, but the same beans in the k10 have a more mature, evenly rounded flavor, more midrange and bottom richness, much more satisfying in my opinion. Then.... it froze again
Disassembly... it looks like what I had feared in the beginning is happening. The delrin is just too soft, it flexes a bit too much. Normally that's not a problem, because it springs back. But in this instance, with very lightly roasted beans, the grinder is under a bit of pressure and the inner burr is moving slightly... the center tightening/holding screw for this burr is reverse threaded, against the direction of rotation; so when the burr shifts, it serves to actually tighten the screw more, a self-correcting feature. As a general rule I don't like gorilla-ing my bolts and when I make errors, its usually leaving the screws a tad too loose. This has come from a lifetime of OVER tightening things and stripping them, and then having to fix THAT. Much easier to just tighten a bit more, ya know.
Anyway, in the stock design there is the aluminum body of the spider to tighten down against. In my modded design there is the delrin spider, which is low and flat, and the inner burr against it presents a wide, flat surface with very light loading, so it won't squash the spider at all.... but the delrin bushing, on the other had, is long and thin, and all that pressure is supported on the bottom of that bushing; so I examined that part closely, here is a pic:
can you see the ridges pressed into the bushing? this is the very bottom of that bushing, its upside down in the pic. This part rests against the stock spindle's shoulder and must support all the weight of that screw, and the turning torque exerted by the burrs... obviously its failing to do so and is turning and compressing. Too soft. I don't have brass in this size, ordered some off *bay this morning but don't want to wait for it to come in... this is if I can't figure it out and have to make the bushing in brass. But for now, I've got some ideas that might solve this... its saturday morning, time to get busy in the garage.