ceramichammer

Iluminatri, sorry for the tardy reply. I thought I had email notifications enabled for new replies. From what I can tell, Repetier sends the steps/e value to the controller's memory. I was sure to change the value in Cura and verify that Cura's g-code output had the correct value. I am using a packing density of 1. I am printing PLA at 210-220. I was printing reasonably large objects at 100% fill so this will make an over extrusion problem readily apparent because the extra material has nowhere to go. When I said the filament gets sheared, I didn't mean that it snaps. I guess you could say it is the failure mode beyond grinding and slipping. The bolt will leave crescent shaped depressions in the filament where it was "grinding". It is different failure mechanism than grinding with the stock gear because although it has a lot more bite, once it tears the crescent in the filament, there is little to no chance of it catching again. This is much more preferable to me because it is more tolerant of little errors and let's you know when something is VERY wrong. The pressure plate onto the bolt is pretty tight. Eventually I will move to a roller bearing pressure device but I haven't had success yet. I have not had filament get stuck in the bowden tube from deformation due to the hobbed bolt. When the tube pops out, the head has already been scraping the print for a while, indicating to me that I have compressed filament in the tube. The bed is properly leveled and homed. I have dialed back the lower layer speed a lot (back down to the stock ~20mm/s). It is possible that with a "too fast" lower layer, I was having to bury the first layer into the bed to get it to stick. This still doesn't explain why the problem gets worse as the print goes on. I have not verified X Y or Z calibration. I assumed because my prints are coming out square and straight then no steps are being missed but assuming is a dangerous thing. I will perform a repeatability test on the Z-axis. After much fussing, I seem to be getting good prints at 885 steps/E. I am not fudging the filament diameter. I am torn between "if it ain't broke, don't fix it", and wanting to know what the root cause is. I will do some testing and report back.

I am using a hobbed bolt similar to this. http://printrbot.com/wp-content/uploads/2012/07/hobbed.jpg The bolt was changed out from the stock bolt when I was away so I had just assumed someone had performed a calibration. The machine (more or less) functioned correctly for a few weeks at the default 865 steps/E with the non-standard bolt. We began having issues with the filament diameter which sent me on a wild goose chase troubleshooting the hardware. Using Repetier, I calibrated, checked, and rechecked the steps/mm value to be 980 steps per mm. These measurements were taken before the extruder drive so the deformation and elongation of the filament due to the bolt does not matter. If I use the correct parameters for the Steps/mm and filament diameter, the nozzle physically scrapes across the over extruded layers on every move and within a few layers, the bowden tube will pop out or the filament will be sheared off by the hobbed bolt. The bowden tube has a heavy duty clamp and I'm amazed at what force would have to be applied to rip it out of the hotend. Also, the hobbed bolt is a much more appropriate drive and it does not grind or slip. If there is that much backpressure, it just shears off filament. I'm using Cura 13.01 and standard print settings. I've had to back the steps/mm down to 900 as well as bump the filament diameter +0.1mm above nominal and even now, I still hear scraping every once in a while which to me means it is over extruding. These numbers account for almost a 15% difference between settings that yield a decent print and the settings that they should "theoretically" be. It just doesn't make much sense to me. I know that with this drive bolt, it extrudes 1mm for every 980 steps. I also know the diameter of the filament to +-0.01mm. Is this a problem with the slicer? Where else could this error be coming from?