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Help please - calibration and clunks

Posted by stevo1957 
Help please - calibration and clunks
January 28, 2016 06:41AM

Trying to calibrate the extruder.

When I extrude 100mm with the command: G1 E100
..........the feed starts, then the extruder clunks and the filament feed slows right down and probably only feeds 20mm or so.

Searching around, I found someone who said to put another command. If I use G1 E100 F90
.......it seems to feed well and the clunk noise is gone.
It feeds around 80mm so I will need to do the maths re calibration values.

I can't find out though what the "F90" represents.

I am using ABS with a temp of 230 on the head and 100 on the bed.

Any help appreciated.


Re: Help please - calibration and clunks
January 28, 2016 06:59AM
Hi Steve, the clunks are probably the stepper motor skipping steps. The cause of this is insufficient torque to feed the filament at the default speed.

When you add f90 it is telling the extruder to feed at a rate of 90mm per minute which is presumably slower than your default speed, set in firmware.

Apart from slowing the feed rate, another variable is stepper motor current, controlled by the little trim potentiometers on the stepper controllers. There is a formula for calculating the current based on the voltage at the middle pin of the trim pot (consult the documentation for your stepper drivers). A rule of thumb is that the steppers should get warm but not burning hot after running for a while, when at optimum current.

I hope this is helpful!

Re: Help please - calibration and clunks
January 28, 2016 08:05AM
Thanks Laurence.

Despite lots of Googling I just can't seem to get things right.

I make settings in the software........there are settings in the firmware.......what I think I am sending to the printer is overridden by what is in the firmware......and I just can't get a print successfully started.

All I end up with is a blob on the end of the nozzle. Despite me setting the distance from the nozzle to the bed via the bed screws/springs and the Z axis endstop, it now seems that when print starts, the nozzle is considerably higher from the bed than as per the initial adjustments I made.

I am still to check the z stepper settings as you suggest and perform the calibrations. If the setting of 90 for feed rate does not cause clunks, is this acceptable for general prining with ABS

I'm really struggling with this so all assistance gratefully accepted.

(By the way, any experts out there local - Sydney, Australia - specifically Hills district area? )


Re: Help please - calibration and clunks
January 28, 2016 03:25PM
Hi Steve, yes these things were made to frustrate us! But it makes it more satisfying in the end winking smiley

I am in Sydney but inner west not hills, still not that far away.

I host 'shed nights' on alternate Fridays and one option would be to bring it down and we can have a look at it.

I have been tweaking these things for 5 years so I have learned a few tricks (but still get a fair share of failed prints!)

Re: Help please - calibration and clunks
January 28, 2016 03:45PM
By the way, regarding feed rates -

What software are you using? The feed rates are set in the slicing software, you can start slow and work up. I print abs at 30-45 mm/s (slower for first layer and outer perimeter, faster for infill). The slicing software - I use slic3r - calculates how much extruder feed based on filament diameter, nozzle size etc.

So it should be fine, when you print all the 'f' codes to control feed are in the file.

Z height - you have the right approach, first set the end stop so that it triggers when the nozzle is just about touching the bed in the middle (I aim for 0.1mm clearance) and is level across the rest of the bed. Then the starting level can be adjusted in software, in slic3r it is in the 'printer' tab, z offset. This can be a negative number to make it start lower. Leave the mechanical bits alone and use trial and error in the software instead, try increments of 0.1 or 0.2.

If your extruder feed is not sufficient this can also cause blob. This is calibrated first in firmware - steps per mm - then adjusted in software with 'extrusion multiplier'.

One final thing is bed surface and adhesion, even with everything else right this is critical! I have good success with kapton tape and 'abs juice'. There are other options.

Better go to work now ..

Re: Help please - calibration and clunks
January 28, 2016 08:07PM
Thanks for the additional info Laurence.

PM coming your way soon.


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