OK with everyone's suggestion on the last thread I remeasured the conveyor (infeed) and have the box now picked up at its exact or as close to exact center as possible.
The infeed has its own User Frame, to account for the 1 degree angle difference between it and the world plane.
However, it's doing things quite... odd. this is an R2000ia-125L btw, using HandlingTool, not PalletTool, as PalletTool wouldn't let me teach a different attack/approach for the top layer and thus had a whole layer of position not reachable (it's reachable only through slow linear movements as the tool head is almost touching the robot head at that point.
For one, i used direct entry to teach that user frame and it won't let me change the arm configuration... it says N D B and the manual is not much help about arm configurations (any external resources would be awesome). So, i thought, that's fine. All of my taught positions where N U T. The robot then decided that all my new taught positions were in opposite land. (right hand, upside down). OK so i accounted for that.
Anyhow, now, when picking up the boxes it's using its custom user frame, and when placing, the user frame is a different one based on world at 0,0,0,0,0,0. The placement positions are based on the user frame using math (box width, length, height, all triple checked for accuracy)
In order to make sure the boxes were snug, they approach by coming down from high up through linear movement to a position of -50Y,+50X, then slide into their respective positions from there. That way, any variation in the box side due to bulging would prevent them from crushing eachother in a straight down movement.
However, it curiously stacks the boxes at the right centerpoint for each, but with the boxes tilted a few degrees each(same way each time, so it looks like):
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The drawing cannot really show you that they interlock at those spots precisely, no gaps, like a sort of brick pattern. And i measured the center of each box and determined they were square with eachother on placement.
I cannot fathom why it is doing this. There's no reason that the boxes should be at an angle since they're all going on the same plane together.. even if the plane was crooked compared to world, they should still stack like ||| except at an angle relative to the world, correct?
I have no idea what I'm doing because I'm an accountant who was told to make the robot work. So if anyone knows what I'm doing wrong, please I'd love a response. Also, a recommendation for online courses to teach me about how to do this stuff....