The firmware default for a Velleman K8200 is set to 600 steps per mm, which is wrong. By making careful measurements, I corrected mine to 700 steps per mm. But using the correct value for extrusion rate requires you to use correct values for the other parameters also, especially the widths that appear under the “advanced tab” for slic3r print settings. Simply correcting the extrusion rate and sticking with the other Vellemen suggested default parameters WILL NOT WORK!
What I did was simply return to the default rates suggested by the people who wrote the slic3r software. Because the Velleman default extrusion rate is wrong, the widths were changed to compensate.
So, the procedure is very simple:
- Measure your extrusion rate.
- Correct the extrusion rate in the firmware either by recompiling it, or through the LED panel.
- Return to the correct defaults for widths under the slic3r advanced tab in printer settings.
This fixed almost all of the problems I was having producing quality prints with the K8200. The machine is not bad - it is the Velleman default setup parameters that are bad.
Why bother? Aren’t any set of parameters that work OK? Only if you are content to print the same thing over and over again. With something as basic as extrusion rate incorrect in the software, the parameter tweaking that works for one print will most likely fail for a different print. That means going through a calibration exercise and tweaking parameters by trial and error for every print job. Picking parameters then becomes an empirical process with absolutely no basis in theory, so you can throw away all the books you bought.
It is a superior approach to set the correct value for extrusion rate. Nobody would try to print with the X, Y, or Z axis incorrectly calibrated, would they? Once the extrusion rate is corrected, then the other parameters behave predictably as described in all the literature. For example, you can play with the bridging speed to try to improve your bridging performance.
Don’t forget to tighten your extruder wingnut VERY SECURELY to avoid fiber slipping! With a “not tight” wingnut, I measured extrusion rates all over the map. Keep tightening and measuring until you get repeatable results.
My suggestion to ALL users (and to Velleman) is to calibrate the extrusion rate, and return to slic3r defaults for widths. Don’t forget, the widths were “fudged” only because the extrusion rate is wrong.
Art Cominio