Splice in the feeder?

When there's about 1-2 meters of material left on a PVC roll the SD300 usually stops and asks the operator to replace the materials. After removing the used roll I recently noticed what appeared to be a double-thickness where two sheets of PVC were spliced together. I believe this is how all kinds of rolled media are typically manufactured such as paper, tapes, newsprint, etc. I guess the SD300 is programmed to leave a little bit of material on the roll to avoid pulling a splice through the feeder into a model. But could it happen anyway?


I had a weirdly malformed build last June. Now I wonder if it was caused by pulling a splice into the model?

When I'd partly peeled the model there was a giant gap in the support material (right) and the model was slightly split. The model was otherwise okay so I didn't worry about it, but luckily I saved some pictures.


More evidence.

While peeling that model I found a piece of leftover support material that seemed to have a double-thickness along one edge. Was this a splice? It seemed odd enough that I took a picture of it.


The SD300 software archives all the machine's activity so I went back and reviewed the 7 June 2010 logs. (I knew when it occurred thanks to the date on the pictures.) There were several new bits of evidence:

• During the build I had paused the SD300 at layer 41. I think I remember putting in a low PVC roll to use it up.
• At layer 50 it had used up the entire roll and pulled the end of the material into the feeder, causing the feeder to jam. I'll bet it had pulled the splice into the model at this point.
  
• At layer 51 the cutting knife broke. It was a well-worn knife so the breakage wasn't unexpected, but I'll bet it got broken by the splice in the previous layer.
• At layer 68 the iron bridge unexpectedly moved on the Y axis, causing an error. I don't really understand the significance of this, but that's the only time it happened in over 600 logged builds.
  

Mystery solved 11 months later?

Maybe. Regardless, I learned several useful principles from reviewing these pictures and logs:

• Don't reload a nearly-empty PVC roll. The SD300 needs to build many layers before it can accurately calculate how much media is left on the roll, and a low roll could run out before that. Saving a few meters of PVC isn't worth ruining a model or breaking a cutting knife.
• If the SD300 does completely empty a roll, check to see if a splice got pulled in. It's probably not common, but I would've cancelled the build if I'd seen it.
  
• When a cutting knife breaks inspect the model to see if there's anything irregular. The breakage might have been caused by an unusual bump or bubble.