Just had my new MINI arrive today & almost everything is working great.
The only problem I’ve had with the few prints I’ve done is the dimensions
are a bit off & it appears to be over-extruding.
Each layer looks like it’s putting down more filament than it needs to be.
I’m presuming this can be fixed by changing the “E-Steps per 1mm filament”
setting although I’m not sure what to put for this; I was hoping someone
might be able to suggest a suitable value to start with so I can experiment.
As for the dimensional instability, I just printed a 18x18x18mm cube as a test.
It came out (roughly) 18.5x18.5x18, oversized in the X & Y axes.
I know I’m not going to expect micron tolerances from a FFF 3D printer,
but I also printed a reduction gear assembly which includes all the parts
separately for you to assemble after printing & nothing fit together.
Holes were undersized & the rods to go into them were oversized.
Anyone got any suggestions?
The Esteps should have been calibrated at the factory. I think you are actually needing to update your extrusion multiplier to dial in the extrusion width.
Basically set your slicer to use a fixed extrusion width, then print a single perimeter hollow box. Use calipers to measure the width of the perimeter. Adjust the Extrusion Multiplier based on the difference. e.g. Extrusion Width of 0.5mm, Measured 0.55mm, set extrusion multiplier to (0.5 / 0.55) = 0.909. Reprint the calibration cube to confirm.
There should be many calibration threads in the forums to give you more details as needed.
Thanks!
Steven
Thanks wantmys2000, I would do exactly that, but I forgot to mention I was sticking (for now at least) to using Cura.
It gives you the option to set an alternate motor steps / mm out of the extruder.
Effectively it has the same effect as changing the ‘Flowrate’ value in Repetier Host.
I had a look in the firmware & the default steps & E is set at 833.
Then it was a case of dialing it back from there then seeing how it goes.
First I tried taking it down 5% to about 790, but taking it down gradually didn’t help.
Next I jumped it down to 500, which was too far.
Then I pushed it up to 600 & the problems I had earlier went away.
I think putting it up a bit (maybe 650?) might be a good idea.
Ultimately, I think I’m sorted.
(just you wait until an hour or so from now & something’s gone horribly wrong 
)
Thats a rather drastic change to the steps per mm and sounds wrong. Can you check your hobbed bolt to see if the grooves are packed with plastic?
PLA is typically around a 90% multiplier from a calibrated steps per mm, ABS should be dang close to dead on. You are at a 72% multiplier.
Another thing you can do is put a line on the filament with a sharpie about 100mm away from the top of the hotend and extrude 10mm. That line should now be 90mm away.
EDIT: One more note, you need to make sure you measure your filament diameter and compare that to Cura’s setting.
It was brand new 2 days ago, I haven’t done enough to mess up the extruder gear yet.
(I checked anyway & it looks fine)
As it is, you may be right about the filament diameter.
That being said, regardless of what is different, It’s now working near perfectly 
I may at some point go change the filament diameter setting in Cura & test the extrusion length,
but I’m now afraid of going away from what I know works well.