Extruder Calibration

[greens83 5]

Hello,

I understand the concept of calibrating the extruder but cannot find anything telling me how to extrude 100mm of filament. Can I do this via the Ulti controller ? when I press extrude on the move axis>extrude command it extrudes way more than 1mm as stated in the ultimaker wiki. Do I have to write some G-Code ?

[pablobell 0]

You can take away the bowden tube, put the filament in the motor, make a mark in the filament and run this code:

 

G91  ;relative positioningG1 E100 F300 ;extrude 100mm at half max speedG90 ;absolute positioning

 

Make a second mark in the filament, take it away and measure it. I suggest extruding 1000mm of filament in order to get better precision.

And tell us the outcome of your calibration!

[greens83 5]

Thanks, I will give this a go this evening. I assume to extrude 1000mm I just change E100 to E1000 ?

[greens83 5]

Ok so when I tell the Ultimaker to extrude 100mm it actually exrudes 102mm. What do I need to change to make it extrude 100mm ?!

Thanks in advance for any help here, I am a complete novice in 3D printing !

[joergen 2]

Ok so when I tell the Ultimaker to extrude 100mm it actually exrudes 102mm. What do I need to change to make it extrude 100mm ?!

 

the default e-steps/mm is 866. your new/correct e-steps/mm would be 866*(100/102)=849

if you set this into the FW, or via the UC menu, you should be good.

[greens83 5]

Thanks. I wasnt sure how to change the value in the firmware or via the UC. Instead I modified the g-code like this:

M92 E848.909

G91

G1 E100 F300

G90

This then extruded 98mm ! Im now very confused.

Any help would be very much appreciated. Is modifying the g-code the wrong way to do this ?

[joergen 2]

Thanks. I wasnt sure how to change the value in the firmware or via the UC. Instead I modified the g-code like this:

M92 E848.909

G91

G1 E100 F300

G90

This then extruded 98mm ! Im now very confused.

Any help would be very much appreciated. Is modifying the g-code the wrong way to do this ?

maybe you did something wrong measuring the 102mm? i would go back to the 866 and leave it at that.

[greens83 5]

I took the same measurement 3 times (102.7mm) 3 times using the code prefix M92 865.888

I used digital calipers and a steel edge to keep the filament straight, I dont think I could have been more accurate.

865.888 x (100/102.7) = 843.123

So I then used the code prefix M92 843.123 and got varied measurements each time I extruded,

the filament shows no signs of slipage, the delrin wheel is tight.

Im very very confused. Is the M92 code prefix the best way to do this ?

How do you change the e steps per mm in the UC ?

Is 102mm accurate enough ? My prints do show some signs of over extrusion.

Im going to try again this evening and flip my filament around just to make sure the slightly abrased side has no impact.

[msurunner 2]

Simple solution for ya: 866=102.7mm, 843=98, try 852. That should get you pretty close... You should be between that and 853 without having quite as precise of an 843 measurement, getting you within one step per e ought to be sufficient to get nice prints.

[greens83 5]

Worth a go but 852 extruded 97mm ! What is going on, surely increaseing the number of steps should increase the amount extruded !? Im close to giving up on this and accepting 102.7mm. My prints show over extrusion though :(

Can anyone make any suggestions as to what I might be doing wrong ?

[pablobell 0]

Could it be that when you measure the filament you use more force for straightening it and it is stretched more?

Are you using the same segment for the measurements over and over? My guess is that the first time the filament crosses the wheel it might get stretched a tiny bit due to the marks and pressure (as in cold forming), but it should be very little.

What part of the machine are you using as a reference for marking the filament? the bowden tube quick release has some wiggle, so take that in consideration.

I'm out of ideas...

[greens83 5]

Thanks for the reply Pablo, I am marking the filament at the underside of the extruder to avoid the wiggle of the bowden connector.Ive been using a new section of filament each time.

Im sure Im doing it accurately its the maths that isnt working. Adjusting the steps per mm in the g-code pre-fix just doesnt seem to be doing what it should.

[snowygrouch 1]

Hi,

By all means do your best to calibrate it, but dont go nuts over it. Remember that how much filament

is ACTUALLY extruded (regardless of how many turns the wheel makes) will also be a function of

hotend temp, filament diameter (which is varying continually) and so on.

You would have thought that if the wheel turns for 100mm plastic, then it MUST come out the nozzle

because it went IN...right. In my experience if the back pressure on the filament (due to forcing through the hotend) is sufficient it will cause a small but measureable amount of slippage on the knurled bolt.

So measuring the "100mm" to within less than say...+/- 1mm is not going to actually give any benefit, because the filament diameter will anyway change in 30mins printing to the state where its behaving differently.

So do calibrate, but be realistic about what the benefits are beyond a certain level of accuracy. Until someone comes up with a sensor to measure filament thickness during printing and links it to the controller to dynamically alter feed rate - occasional under or over extrusion will be a fact or life.

If you are lucky you can get the Steps Per E set so its about in the middle, so in the end that a little over or under extrusion wont really be a big issue for the actual printed result.

Because the extrusion test does not take account of the hotend force, the best way forward (well ok, ONE way forward), is to to the 100mm test to get you close...then just print stuff and tweak the number in the code prefix yourself until it looks good. So probably (as has been said already), just do the 100mm test, enter than number, test it then adjust up or down a bit (try say, adding + or - 20 or so at first). Its good to move more than you think so that the result is more clearly apparent. If you sit there all day moving it around by 1 or 2 you will not see the result clearly enough to see which direction to go in.

C.

[greens83 5]

All good points, perhaps I should just forget about calibrating the extruder.

But I still cant help but be perplexed by the fact that changing the E-number by the exact percentage of over extrusion doesnt correct the amount extruded. (All with Bowden disconnected so hot end pressure and slippage are out of the equation), its not even close when the correction is made in the g-code prefix.

Default E stpes per mm extrudes 102.7mm.

This should correct the 2.7mm over extrusion: 865.888 x (100/102.7) = 843.123

But it doesnt. What is wrong with this calculation ?

[snowygrouch 1]

I dont know on that why its not changing, just be careful with if you are overwriting files on the

SD card. I very often have a really wierd problem when I save G-code over the top of the same

filename on the SD card. It claims to have overwritten the file, but it them prints the old code !

So just check the text in the code file, to make sure its really different. Then also do a big

change, just to see what happens. So add 100 or something just to see if its really that the code

isnt doing anything.

It would help alot if you posted the code you are putting in the machine.

C.

[greens83 5]

Ok, Id not even considered the SD card overwrite issue you have found. Il try again with fresh G-code files this eveining.

The code I have been using is:

M92 865.888

G91

G1 E100 F300

G90

I was changing the M92 xxx.xxx to adjust E steps per mm.

[snowygrouch 1]

Hmm well that should work !

Just try changing it by ALOT and seeing what happens then. Also if you have an ulticontroller be aware that if you have twiddled with the extrusion rates in there it will skew everything one way or the other. But that wont stop it having an effect at all, so thats rather confusing. As before, just try changing it by 100 and see what happens then.

If nothing happens then - I am then at my limit of ideas.

[illuminarti 18]

I think the correct syntax is M92 E865.888 - the M92 command allows you to specify values for any of X, Y, Z and E. Without the E specified, the value just gets ignored.

 

The code I have been using is:

M92 865.888

G91

G1 E100 F300

G90

I was changing the M92 xxx.xxx to adjust E steps per mm.

BTW, there has been a discussion over on the Google group (

https://groups.google.com/d/topic/ultim ... discussion

), that the current correct value for the steps-per-e (assuming a Bertho (spring) extruder tensioner and a v3 bolt, is somewhere round about 832.