The Z screw is indeed misaligned a bit. We discovered this a few weeks ago, but on normal sized printers it doesn't cause any real problems. I think it's the result from the drawings being done in Illustrator instead of a CAD tool.
As snowygrouch already pointed out, it's very important that the bronze "nut" is lose. The leadscrew we use is never properly centered (it's almost impossible to create them perfectly centered) if you fix this firmly in the platform you will get ridges that exactly match the thread pitch.
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snowygrouch 1
Yes the shaft centres are 3mm misaligned.
I dont know exactly why this was done, but my best guess is that they like the z carridge to stretch horizontally
to give it some preload on the bearings to be stable. You can see this because the left side of the Z carridge is flexible and has been designed to flex outwards to be able to fit to the shafts (which are 3mm wider than the bearings in the Z carridge).
The area around the nut has been made intentionally so that the bronze "nut" can move about, if you dont do that, what happens is that the lead screw will wobble the whole z axis carridge about, because its pretty wonky by the time its been coupled to the Z motor. So dont fix the bronze "Z nut" because it will just make your table wobble as it goes up and down.
It doesnt really matter that its loose in there, because gravity is keeping the table down anyway, and the table only goes down during printing. If it were having to do direction reverals, that would be a big problem. But it doesnt..so.
I do admit though, that im my opinion the z carridge design can be improved alot. Its not very solid generally
and could do with beefing up. This is one major reason behind layer misalignment on tall prints. I have seen some
people bolting on stuff to the flexible LHS of the carridge to stiffen it up.
Its not great, but there are a half dozen things to improve before you need to start worring about the z carridge.
C.
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