Extrusion Lenght inconsistent

[jweaver 2]

I have been struggling with the first layer on my Printrbot and someone suggested "under-extrusion".

I know I setup my Printer when I got it and it was spot on.. So today I thought I would check.

I marked a point on the filament and then fed 200mm (pressing the 10 on CURAs PrintUI GUI 20 times) and I measured only 195mm.

So I tried again and each time I get anything from 188 to 196mm fed.

Does anyone know why this is? Is the extrude button OK for doing this? Perhaps pressing it several times is flawed?

Jon

 

[IRobertI 520]

I'm not familiar with the Printrbot family of printers (and this being an Ultimaker forum there might not be a whole lot of people that are) but I'm guessing the usual applies. Check the nozzle, is it clean? Check the feeder bolt. Does the feeder tension need adjusting? If you feed material into the air (not sure if that's what you were doing), does it still come up short?

 

[gr5 2,167]

Is the filament going through the nozzle while doing this? If so then 6% (188 versus 200) underextrusion is fine and won't be visible in the print. What happens is the splined (or knurled) wheel that pushes on the filament digs tiny holes into the filament. The filament gives a bit such that you loose a little bit of forward momentum. The more you are losing the longer the holes get until they connect and you get slippage.

 

[gr5 2,167]

Images of almost zero slippage (< 5%):

 

 

[jweaver 2]

I watched the filament really closely and it turns out it WAS slipping.

So I have adjusted the tension and am going to try again..