I've got a home built delta printer, loosely based on Rostock, controlled by a RAMPS 1.4 board running Marlin firmware. It works fine, and has done for quite a while. It prints straight and level. The calibration is correct. Until, that is, I print something larger than about 175mm in the x or y direction. As soon as I do this, the whole print takes on a slant, as if a constant x increment were being added at each layer. The slant is uniform across the whole print. It's like printing in italics. If the print dimension is slightly smaller, say 150mm, there is no slant at all. There are some pictures on my blog (http://robinsonia.com/wp/?p=335) if you want to see. I have tried test prints sliced with both Cura and Slic3r; both behave the same. The on/off nature of the problem makes me think it is not a hardware problem - I would expect distortion to appear gradually if this were the case. My suspicion is that there is an issue in the Marlin firmware, and that somehow it is losing track of the motor steps, or perhaps there is a cumulative rounding error which only becomes important above a certain size. I've googled, of course, and no one else seems to have encountered this issue. I've recalibrated, rechecked all my settings and made sure the the Marlin firmware is up to date. Smaller items print fine. I'm basically stumped, and I really want to print some bigger items.
Do any of you experts have any thoughts on what might be the cause of the problem?
Do any of you experts have any thoughts on what might be the cause of the problem?