Don't Over-tighten the Material Feeder!!!

this is what happens when feeder tension is too high

Summary: Over-tightening the material feeder will cause the filament to slip and will lead to under extrusion.

Yesterday morning I made the nice print pictured above with the normal quality settings. That evening I tried to make some more prints. They did not look good.

Multirotor helicopter foot.  WTF!

The picture above was the result of a normal quality print. Looks like under extrusion again. I was already printing at 220°C so I didn't think temperature was the issue. It was a model that I designed from scratch so I thought maybe the problem was with my model. I downloaded a popular whistle model from Thingiverse and tried again. This time I used the full settings so I could change the layer height, number of layers, and infill as directed.

not even close

As it was printing I could hear some clicking coming from the material feeder as the knurled wheel slipped on the filament. I thought the tension on the material feeder might not be high enough so I tightened it until the indicator was on the center line. No improvement. I canceled the print after about 30 minutes; the layers were a mess.

reducing resistance on spool

I thought the nozzle might be clogged but before I tore it down I decided to check the UM forum again and search the under extrusion posts. I noticed that under extrusion can occur when the coils on the filament spool have trouble unwinding. This seemed particularly common with Ultimate-Blue PLA as it seems stiffer than some other brands. So I removed the spool, unwound a bunch of coils, and tried to straighten the filament as best I could. Then I tried printing the multirotor foot again.

proper tension setting on the feeder

With the machine back facing me, I noticed the material feeder slipping about every 5 seconds. With the better view I could see how too much tension (rather than not enough) could lead to the slipping I was seeing. So I backed off the tension until the slipping stopped. The material started feeding just fine, no more slipping.

that's better

The foot printed perfectly. Thinking back, I believe the first thing I did to combat under extrusion was increase the tension on the material feeder when I should have been increasing the temperature. Keep in mind there are two different versions of the material feeder for the UM2. There is an older version which apparently had some problems and needs to be adjusted to about the middle setting. And there is the new version which I have which likes to be set towards the top. This setting is much more critical than I expected and I wonder how many under extrusion problems are a result of improper tension on the material feeder. Check this first as it can save you the trouble of cleaning your print head!