I’ve been having an intermittent problem with my printrbot simple metal in which it seems multiple layers are being squished together. To get a better idea of what’s happening, take a look at the attached photo.
The incidents begin with a cracking sound caused by the extruder nozzle being on the same z axis plane as the top layer (or few layers) of printed material. It seems like the Z axis is not moving up far enough at points in the print which causes the layers to squish and the extruder nozzle to impact printed plastic.
As I mentioned earlier, the problem is intermittent making it even harder to diagnose. Some tall prints come out great. Other prints have squished layers but the printer seems to correct itself and finish the print. I thought it may be a stripped z axis thread, but the layer squishing happens at all different heights.
In the case below, the line near the top of the sphere was caused by an incident like this, but I caught it early enough to intervene. I paused the print, moved the z axis up about .3 mm and then used G92 to tell the printer its z axis was at the height it had previously thought it was at. While it worked for the first incident of this print, I wasn’t lucky enough to catch the second and the sphere was eventually knocked off the bed by the print head.
Maybe the Z axis motor is loosely connected so not all “go up one layer” commands from the controller board will be executed.
Otherwise you should definitely check, that your flowrate is proper and you should check the filament diameter (just to be on the safe side).
If the issue isn’t in the mechanics or electronics then I’d suggest to upload new firmware to your Printrbot, maybe the Z axis scaling isn’t set correctly* or any other setting in Marlin was wrong.
*This should cause all layers to be printed badly, but check that anyways.
I’d advise you to connect the Printrbot to your PC and then you should tell the printer to lift / lower the Z axis via the PC, move the printhead to the minimum and maximum of the Z axis several times, check for any mechanical issue, apply grease to the rods and in the worst case you should consider disassembling the axis to replace the bearings or similar. Check for any dirt accumulation along the moving parts and make sure the electronics are connected and protected properly. The wires should NEVER be streched to the limit when printing (ie when the Z axis is moving to the highest position it pulls heavily on the cables), also use spiral tubes to group the cables and secure them with cable ties.
