Extruder E-step Cal Inconsistent Results

[Drone]

After getting my i3v 10" working very consistently with what I consider acceptable print quality (BIG thanks to Roxy and DACB for the autobed leveling code work), I thought it was time to do some fine tuning to see if I could get even higher quality prints. So, last night I started going through the calibration for the extruder following the ZennmasterM videos and after 3 hours of effort was getting wildly different results after each attempt. I started with extruding 97.6mm of PLA (used pronterface to extrude 100mm) and made adjustments from there using Zenn's calcs, and after making the estep adjustment to 861.7 by using the LCD controls wound up with a measurement of 95.6mm extruded. Huh?

Long story short, I reset estep to 841 and did 5 100mm extrudes and got varied results with every extrude, up to 8mm of difference between extrudes. I tightened the guildler screws and that had no effect. And like I said, I'm actually getting very good prints. I also made 10 measurements of the filament over the 100mm of PLA to be extruded and had a consistent 1.73mm. So I was wondering if anyone has run into this before and has any suggestions.

[AbuMaia]

What are you using to measure the filament run through the extruder? I printed out this thing http://www.thingiverse.com/thing:114614 minus the slider, marked it in 10mm increments, then used it to mark and measure the filament above the extruder. I ended up using 900 for my esteps.

[dacb]

I too had an e-steps in the 900 range. See the Configuration.h in the github fork for what I ended up using. I will say that the kind of behavior you are seeing could be from a loose gear on the extruder stepper. Where the set screw engages on a forward extrusion but slips on a retraction. This would make calibration seem consistent (continuous forward feed) but prints are effectively uncalibrated.

[AbuMaia]

I do need to recalibrate my extruder. I just noticed two days ago the large gear on my extruder was very loose on the hobbed bolt. I could turn it a good 5 degrees without the bolt moving at all. I've replaced it, but haven't recalibrated yet.

[Drone]

Thanks for the replies all. I have been measuring the filament above the extruder like in the Zenn videos. And with the extruder steps remaining constant at the default of 841 I am getting deviations of up to 5mm in back to back extrusions. I have checked the large extruder gear and it has no wobble, so is tight on the hobbed bolt and the gear mesh is not loose. The extrusion when viewed during the extrusion appears to be very smooth with no interruptions or gear chatter. Also, the extruded filament from the hotend appears to be of uniform thickness and extrudes straight down. Tomorrow night I will try removing the Hexagon hotend and extrude raw unheated filament and measure to see if it is a backpressure issue.

One interesting thing to note is Zenn said he was extruding PLA (as was I during the testing), but he had the hotend set to 230c. That is much hotter than I would normally print at with my temp at 185c, and that was the temp I did the testing at. Does this test require a higher temp to reduce any backpressure influence on the test, or is 230c a reasonable temp for PLA and I'm just doing it wrong? I suspect he misspoke and was extruding ABS, but I don't know.

To be clear, I am actually very happy with the print quality as it is now, especially after getting the ABL system working. I am just searching for even better if it's possible. Who doesn't want better right?

[printbus]

First, I've learned I get more consistent results if I toss out the first long extrusion. Make sure the guidler bearing spins free with no filament in the extruder, that the filament spool has little or no drag, large gear isn't rubbing on the mounting bolts for the top two delrin wheels, etc. Before you installed the extruder, did you make sure the filament feed hole in the base doesn't have loose filament stands from being printed on the side?

Temperature is relative on these repraps, not absolute. I can say that I have one spool in particular of PLA that will stop extruding if I tried to print at 185.

[Drone]

Good ideas Printbus. I'll check those items tonight and see if there are any issues.

[Drone]

OK, I finally have consistent results. The issue was the Greg's extruder/Hexagon hotend .4 nozzle combination can't deliver repeatable results at 100mm/min extrusion rate. I switched to 65mm/min and the results of 3 tests at the default estep setting of 841 was 24.95, 24.91, 24.95. After adjusting to an estep setting of 884.8 the next 3 test showed 19.89, 20.13, 19.93. Well with the margin of error for the width of the marker I was using to do the measurements. I haven't done any testing between 65mm/min and 100mm/min to determine what the maximum feed rate is for consistent extrusion for this extruder/hotend/nozzle combination, but I'm now confident that at 65mm/min I will get good results. This is why I was baffled by the early testing results and yet had by my standards very good prints. I have always had the perimeter FR set to 65, so it was within the consistent range of the hardware. I may have to get some different nozzles to see if this behavior is nozzle diameter limited, or if the higher feed rate deviations exist in the extruder or hotend. I'm going to do a few prints of items I have already printed at the old estep value to see if I can see a difference in print quality. BTW, the Zenn video showed a 100% FR on the LCD controller, but never showed what he had set as a FR in Pronterface. So I have no idea what FR he was using for the test.

[TopJimmyCooks]

I use an exacto knife to make a small cut in the filament to mark length measurements for calibration.

[orionthunter]

I prefer to calibrate my extrusion from prints. I print a small box with 0% infil and no top/bottom. I use a layer height of .3 mm and a shell thickness of .45mm. I measure the actual thickness of the wall and use that to adjust my E-steps.