I have had my Mini since December, and it’s been relatively trouble-free. Today, however, I experienced some isolated but significant “Y axis layer shifting”.
The model was http://www.thingiverse.com/thing:1340784. I was using 0.30mm layer height, and scaled to 80% so the model was about 125mm tall.
Everything printed perfectly up to about 85mm (i.e., up to around layer ~283).
Over the course of the next ~4mm of Z (so layers ~290 to ~303), there are several layer shifts evident where the Y position increased abnormally. It wasn’t a single shift; rather it appears there were about 5 or 6 separate +Y shifts that occurred during the course of those 12-14 layers.
The rest of the model (from ~89mm to 125mm, so ~120 more layers) printed without any further Y shifts. Of course the Y shifts that occurred between Z=85 and Z=89 mean the upper portion of the model is offset by about +20mm Y.
So what could cause several +Y shifts in this isolated area of a print?
Here’s what I’ve checked/considered so far:
- The Y-axis pulley is in the correct position, grub screws are tight, motor screws are tight.
- The Y-axis belt looks perfect, no wear or missing teeth. Idler moves smoothly.
- The Y-axis belt tension appears normal, same as when delivered and similar to the X-axis belt tension.
- The electronics cooling fan is running, vents are clear with good flow out the back vents, room temp is 68F (20C).
- The bed moves normally, no binding or odd noises, no problems on any other prints (and no problems on most of this print, before and after the narrow Z range where the Y shifting occurred).
- There was no outside interference during the print (no pets, kids, etc. in the house)
- The Y-axis stepper does get pretty hot, like ~65C, but from what I’ve read that is pretty normal.
- Firmware is stock, as delivered from Lulzbot.
- Slicing and print control was via Simplify3d. I saved the Gcode and loaded it into a visualizer, and it looks fine so I am confident that the Y shifts are NOT in the Gcode (i.e., not a slicer problem).
What else could cause sporadic Y axis shifts like this?