Extruder Calibration Frustrations


I recently began to work with bridge nylon filament on my Taz 5. I haven’t made any hardware modifications, nor have I updated the firmware. I’m starting to take tolerances into account, so I decided I would look at proper calibration. I also understand that a nylon filament might not be the best to calibrate with, however, I will be predominantly printing in nylon, so it seems sensible to calibrate for it.

Calibrating the extruder is quite frustrating and tweaking the Esteps seems completely arbitrary on my machine. I’ve been following the OHAI guide. My Esteps was set to 860 by default. For the following results, I ran 100mm length and 100 mm/m speed five times, then took the average. At an Esteps of 860, it was typically under-extruding by 55-60mm. At an Esteps of 760, it under-extruded by 50mm. At an Esteps of 660, it under-extruded by 50mm.

Since that wasn’t making much of a difference, I went in the other direction. At an Esteps of 1060, it under-extruded by 50mm on average. I’ve even cranked it to an Esteps as high as 1460 (under by 100mm) and as low as 460 (under by 55mm) and my results got me no closer to a calibration. Every time it would under-extrude. I’ve also raised and lowered the extrusion speed and I’m still getting wildly inconsistent results.

I’m hoping there is some obvious thing I’m doing wrong. I’m sure I need to provide more information, but I’d appreciate a push in the right direction.

I would use about 50 MM/sec print speed since that is about what Nylon uses. YMMV.

I’m also trying to calibrate my extruder (using ABS) to see if I can try to track down some issues that I think might be related to under extruding. It came preset to 833 and I find that it would only extract 66/100 mm. Using that, I cranked it up to 1262 based on the OHAI calibration page. That only improved it to 76/100 mm. I’m hoping that there’s something obvious that I’m missing but 1262 seems higher than should be reasonable.

Try cutting your extrusion speed in half, or more.

If that improves things you’re extruding too fast for your system to reliably do.

Then you need to look at the idler tension to see if it’s high enough to reliably engage the hobbed bolt teeth, verify the idler bearing turns freely, check for clogged hobbed-bolt teeth, check heater block temperature (too low and the plastic is too viscous to be pushed fast through the nozzle), check for a clogged nozzle, look for drag on the filament anywhere in its path including where it comes off of the reel, etc.

In the hopes of helping someone who might come across this thread later, one thing to keep in mind is that while calibrating in Pronterface, we are using an extrusion speed that is measured in mm/m. So if I plan on doing my standard bridge nylon prints at 50 mm/s in Cura, that would be around 3000 mm/m. Is this correct?

So if LulzBot tells me to use 100mm and 100 mm/m, it seems like deviating from that will make it harder to be consistent in how we calibrate. I feel like we should be limiting the variables, not adding more. Since this kind of extruder calibration is taking into account the amount of filament fed into the extruder and not the amount actually extruded, do we really need to consider the desirable Cura printing speed of a filament?

I will begin looking around for information on the idler tension and those additional suggestions. I understand that some of my assumptions in this post might be way off. I’m only just beginning to get a decent grasp of these concepts. Up to this point I’ve been satisfied with the stock calibration and the standard LulzBot Cura profiles. However, since I’m getting into custom gearing, I need to be able to anticipate tolerances in order to make sure a print comes out how I need it to.

I didn’t use pronterface as I didn’t want to install something just for an extruder calibration. I just used gcode in cura, which worked fine.

G91 ;relative movement
G21 ; set units to Millimeters
G1 E100 F75 ;extrude 100mm at 75mm/min 
G90 ;absolute movement

Feedrate is a little bit quick there. Drop that F200 to an F75 and you should be good to go.

Thank you for catching that. I had adjusted it when I ran it but didn’t put that part in my notes so I forgot. I’ve updated my post.

After more frustrations with just modifying the Estops and getting no where, as recommended above, I started looking at the physical set-up of the extruder system. The first thing I decided to calibrate was the idler tension springs. It turns out that was the only thing I needed to mess with in order to get a perfect extruder calibration. I feel silly for not doing it sooner.

Our Taz 5 is a publicly used machine, so numerous people load and unload filament. The tension on the idler springs had become way too loose. I tightened them until they felt snug, but it wasn’t too hard to unclasp the idler. The inside measurement from washer to washer was around 8mm, so I dialed them exactly to that number.

While researching this, I noticed that someone made a tool to help get the springs to 8mm, so it appears that’s perhaps a solid number to aim for with the idler tension springs. With an Estops of 916, I now get exactly 100mm of filament every time.

So the trick wasn’t to deviate from the OHAI guide; I just needed to make sure my screws and springs were also being considered in my calibration.