I have a huge problem with my Anycubic Kossel Linear Plus.

I’ve calibrated the bed using the autocalibrate feature in Marlin and it seems to work ok. Print quality is ok and Z dimensions are spot on. Getting std.dev of 0.021…0.035 which i think is good. (or is it?)

The X and Y are not. For whatever reason is I try to print 20x20 cube, it comes out something like 20.5 x 19.5. Most topics about scaling issues involve identical shrinkage / bloat in every direction, but here it’s not the case.

I could fiddle around with diagonal_rod value, but i am afraid that the bed calibration will go to hell, am i correct? Also, since the common solution to X and Y being off by the same ratio is changing diagonal_rod, it won’t help in a situation where X and Y are off in different directions, am I right?

I’ve made sure that machine is square, by disassembling the whole thing, putting the top triangle on top od the base and running tower extrusions through both of them. The I’ve tightened the vertex screws. Machine seems to be square to the bed and the frames. I don’t think the frame is an issue.

I’ve measured the rods and they seem to be withing 0.5mm. Dunno if this makes a big difference, but it seems tome like it shouldn’t (0.5mm on 270mm rod is 0.18% error, so it can’t possible be the reason for 0.5mm error on 20mm dimension (2.5%). Or can it? There seems to be some play in some or the ball joints, but I assume if this was the culprit, the dimensions would be off randomly, not consistently. I still ordered Traxxas rod ends and CF tubes to build new rods.

Any advice is welcome, as I’ve generally run out of ideas what to do next.

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