This jar lid thing is a real puzzler. Yesterday I tried to break one...bending, flexing, squashing in a vice, and all I can think of is that it is somehow temperature related since the plastic is totally impossible to break at least at room temperature. To make that lid I use a die press and die and the temp out in the workspace can be as low as 50F...the top surface is slightly cupped so it flexes when pressed....I am just thinking out loud here since there must be something I am doing to create some weakness in the lid as it seems impossible for the postal services to break the lid without breaking the jar...Currently I build these things in monastic silence to try to hear some little pop or crick sound when I put on the lid and tighten the bolts/nuts.
On that rub....that is why we set up zero, in many ways to try to avoid going into the entire thesis of grinder burrs that exploded on the Pharos alignment issues. To begin, if you tighten the burr setting on your K10 toward zero while running you will eventually get the burrs close enough to grrrrrr them and you immediately back off the setting. The burr rub is only at one spot but since it is spinning relative fast you don't get any more feedback than a grrrrrr sound. The burrs do not touch at all 360 degrees around the radius, just one area on first contact and with a hand grinder one can witness this same thing, but since you can turn the burr so slow instead of grrrrr you hear/feel a rub at one part and instead of just carrying on as with a spinning electric grinder one can go down a rabbit hole of obsessing about alignment. That is a conversation we had hoped to avoid, at least for a while.