Under Extrusion and no found fix

For the past few weeks, I have had little success in fixing an under extrusion problem. The problem started about a month ago and has only gotten worse with time.

the top and bottom infill of prints is under extruded to the point in which if you hold the print up to the light you see an array of dots where light shines through.

I am printing on a FolgerTech 2020 i3. The extruder is a MK9 Direct drive. I am printing with Hatchbox silver PLA and Promolt 3D black. Print temperatures have been tried from 185 c to 220 c.

The first time I tried to fix the problem, I added an extrusion multiplier of around 150%. This allowed the top infill to be solid, but the rest of the print was puffy and over extruded. This was not a good solution.

After reading all about this problem, I determined it was my nozzle, and bought a replacement. After installing the new nozzle, nothing changed.

Then, I found the Teflon tube in my extruder had been melted. While printing with PETG, I pushed the extruder temp. to around 245, and I suspect that this damaged the tube. I bought replacements for this tube, and nothing changed.

I decided to look inside my extruder and found the drive gear had some PLA dust on it. Scraping maybe? I measured the diameter of the gear and found it to be under 11 mm. The firmware states that the extruder steps per mm is 90, but for this ti be true the gear would have to be slightly over 11mm in diameter.

I changed the steps to 105 steps per mm, and this has no effect. If I send "M92 E105", the under extrusion problem improves but does not go away completely.

I have done everything I could think of. What do you suggest on what to do next? Thank You for your time.

Firstly, calibrate your extruder. Mark your filament with a Sharpie about 120mm from the extruder. Command a 100mm extrusion, and measure the distance of your mark from the extruder. Adjust steps/mm so that the distance moved is exactly 100mm.

Secondly, measure your filament diameter. Filament may vary in diameter by 10% or more, even on the same spool.

I have tried the extruder calibration multiple times and when I tell it to extrude 100 mm it does, but under extrusion still happens when it prints. Print speeds are all under 10 mm/s (infill, borders, everything).

While calibrating my extruder, raising the steps per mm sometimes resulted in LESS filament being extruded. Weird, right?

As for measuring filament, I do not have any calipers. I'll probably get some for Christmas.

If you have calibrated your extruder where it takes 100mm of filament when told to extrude 100mm of filament, then the next step would be to try slow your print speeds down. Based on your dust comments, and what I've experienced, sometimes I can extruder 100mm at a stand still, but during a print it will not feed the plastic properly due to too much tension and not enough tension (I know it sounds weird, but both can cause it not to feed the proper amount). If you slow down your print speed and see if its a case of extruder motor skipping while it's trying to feed in filament as that could also cause your under extrusion.

I personally print with Hatchbox PLA and I've used the Hatchbox PLA silver from Amazon without an issue at 190F. I did however change from the MK7/8 drive gears to the geared wade's extruder setup with 45/11 ratio and that seemed to help even more. Previously, the extruder motor would skip steps if it tried to feed too much filament during a print but with the geared extruder I haven't seen that issue since.