Extruder Calibration

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Polygonhell
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Extruder Calibration

Postby Polygonhell » Mon Feb 18, 2013 2:27 pm

IMO assuming you've sorted out mechanical issues, the single biggest difference in print quality comes from calibrating the extruder.
Firstly measure the filament in multiple places, and type that into slic3r
2nd realize that you cannot calculate a correct ESteps value, and the one in the firmware is just a starting point.
Part of the reason for this is that when the filament is compressed in the rollers it changes the effective diameter of the drive wheel, the main reason for this is while the slicer relies on volume in = volume out, it's using an approximation for the extruded profile, and the actual calculation is only as accurate as that approximation.
NOTE that means correctly calibrated for one slicer does not necessarily mean correct for a different slicer.

To my mind there is only one model and 2 print settings you care about to calibrate extrusion, I use the 20x20x10 test cube, though any cube or cylinder would do.
I'm using Slic3r in the following but I'd do the same with KisSlicer or Cura.
Generally I set my extrusion width explicitly, in particularly I don't like Slic3r's automatic extrusion width calibration. I set all of the widths in Slic3r to the same value 0.55 for my 0.5mm nozzle, general rule of thumb being nozzle diameter +10%.
I want settings that minimize other effects on the feed rate so
  • I disable retraction
  • I set all of the speeds to the same relatively low value of 20mm/s

  • I disable any slowdown for cooling (I run a fan always on)
I set the extrusion multiplier to 1.0, set the settings to print 1 wall 0% infill and I print a bottom layer
DSC00064.JPG

I measure the wall thickness in several places with digital calipers, this take a bit of messing around, Ideally you to want to measure it for one layer in one spot to remove any inflation you get from waves in the wall, measure several times throw out unusually high or low values and average the rest, in this case it was 0.65mm much larger than the requested 0.55mm.
At this point I'd normally take 0.55/0.65 = 0.85 and just use it as the extrusion multiplier, print another hollow cube, verify then print a solid cube, but I want to show you how extrusion affects print quality.
The final litmus test IMO for extrusion is being able to print a tidy 100% fill test object.
I use the same settings as above but I set perimeters to 2 and infill to 100% for the test cube, to illustrate in the following picture, I printed from 1.0 to 0.75 extrusion multipliers in 0.05 steps.
DSC00062.JPG

The excess material is obvious on the 100% example and can be see decreasing through the 90% one, the 85% one looks good and if you look closely you can start to see small gaps in the infill and between the perimeters in the 80% and 75% cubes. So apparently my rough calculation above was good.
I would note here that the gap between the left/right edges and the infill is less that the gap between the top/bottom edges and the infill, I apparently have a small mechanical issue, probably one of my ujoints has too much friction, or a belt isn't tight.
What's not obvious is the general effect it has on other aspects of quality here is the profile of the 100 85 and 75% cubes.
DSC00063.JPG

Note the unevenness and generally poor layer alignment of the 100% cube, it's worse in Slic3r than most other slicers because Slic3r only prints perimeters inside to out, pretty much guaranteeing that the outside perimeter is displaced by extra material in the inside perimeter.
The 75% one is cleaner than that "correct" 85% one, because the perimeters don't touch so it's like printing a single wall object, with a slicer printing perimeters outside to in or with only a single perimeter there would probably be no visible difference between them.

Note You can't just take my 0.85 value and use it, you need to measure and print a couple of test objects, the 0.85 is correct for the PLA filament I happen to be using right now on my machine using the version of Slic3r I happen to be using, if I were printing ABS, that 0.85 would likely be higher because the pinch rollers compress it more.
IMO the default ESteps value in the RostockMax firmware is on the high side even for ABS, so if you haven't calibrated, it is affecting your quality.

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Re: Extruder Calibration

Postby JakeCShake » Mon Feb 18, 2013 2:58 pm

As usual.....great topic and great details. Thanks....

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Re: Extruder Calibration

Postby Highcooley » Mon Feb 18, 2013 5:31 pm

Thanks for your detailed instruction. I work about the same way.

However, one thing that always annoys me is the whole filament measuring. Every time I measure, I get slightly different results. I usually take the average of two diameters at 10 points, 10 cm apart, using a digital caliper. But even the measured diamaters sometimes differ by a maximum of 0.04 mm when measured twice at the same spot. So the average can sometimes vary by about 0.02 mm if I measure the same filament twice.

Do you have a special method how you measure? I think, my problem relates to the pressure applied to the caliper when emasuring as well as to the radius of the filmant when unrolled from the spool. I usually measure witht the flat part of the caliper in order not to squeeze the filament too much or pierce it.

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Re: Extruder Calibration

Postby Polygonhell » Mon Feb 18, 2013 6:03 pm

Highcooley wrote:Thanks for your detailed instruction. I work about the same way.

However, one thing that always annoys me is the whole filament measuring. Every time I measure, I get slightly different results. I usually take the average of two diameters at 10 points, 10 cm apart, using a digital caliper. But even the measured diamaters sometimes differ by a maximum of 0.04 mm when measured twice at the same spot. So the average can sometimes vary by about 0.02 mm if I measure the same filament twice.

Do you have a special method how you measure? I think, my problem relates to the pressure applied to the caliper when emasuring as well as to the radius of the filmant when unrolled from the spool. I usually measure witht the flat part of the caliper in order not to squeeze the filament too much or pierce it.


Depends on the filament, I usually use the smallest value measured at any given point and average across the points. But 0.02mm isn't going to hurt much, you're talking about a 1% difference, the cubes above are showing what 5% equates to.
Also if you print calibration pieces and adjust the extrusion multiplier, having the exact diameter is irrelevant anyway, it's just a way to get in the right ballpark.

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Re: Extruder Calibration

Postby mhackney » Mon Feb 18, 2013 6:18 pm

Excellent writeup Polygonhell! I have to say, I was using an OLD version of slic3r and Protorface with my H-1s for the last year. I had them tuned to get very predictable and nice results. When I got the Rostock I needed/decided to get the latest and also use the Repetier host. There are a lot of differences in the latest slic3r and the earlier versions!

One sanity check for calibrating and checking calibration of extrusion is to calculate volume in and volume out. I made a little spreadsheet to do this. I've attached a copy here if anyone is interested.

ExtrusionCalculator.xls
(19 KiB) Downloaded 525 times


Basically, once you determine your filament diameter and have calibrated steps-per, you tell the extruder to extrude 10mm (or whatever) into air so the filament hangs straight down. Then, you let it cool and snap off. Measure it's diameter and plug that into the spreadsheet. The spreadsheet calculates the volume of the input material and the volume of the extruded material. These should be relatively close in a well calibrated extruder. It is surprisingly useful. For instance, when I first setup my Rostock I used the defaults in the firmware for steps-per. I did a 10mm extrusion and discovered that the volume out was 1/2 what it should have been! That led me to discover/realize that the newer RAMBo ver 1.1 has 16 microstep by default!

@highcooley - calipers are not the best tool for measuring diameters for precisely the reason you mention - the amount of pressure you apply affects the measurement. A better tool is a micrometer. It has a mechanism that guarantees the same pressure is used for all measurements. Calipers are generally useful tools for a lot of applications and measuring hard materials like aluminum, they are not too bad. But measuring the diameter of soft materials like ABS or PLA they lead to the irreproducibility you've experienced.

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Re: Extruder Calibration

Postby texsc98 » Fri Feb 22, 2013 11:56 am

Excellent write-up!! I'm going to have to do this on my RMAX... I can tell that I'm getting just a bit too much plastic, it definitely shows up as it gets into the higher layers. I can see it either widening as it goes, or creating extra build-up of plastic on top that it has to try to "smush" down flat with each successive layer. I was planning on just playing with the extrusion multiplier until I thought it looked close, didn't think about using calipers to actually measure it.... brilliant!
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Carbon fiber rods w/ ball joints for Rostock MAX ~$40 viewtopic.php?f=36&t=2165

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Re: Extruder Calibration

Postby cambo3d » Wed Mar 27, 2013 2:43 pm

thanks for this, this helps a lot, maybe put this in a sticky. A long with some others that I probably don't know about yet

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Re: Extruder Calibration

Postby JakeCShake » Wed Mar 27, 2013 2:55 pm

THIS is what I was looking for yesterday to help you guys...
Definitely deserves a STICKY.....

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Re: Extruder Calibration

Postby mhackney » Wed Mar 27, 2013 4:28 pm

I promoted this to a sticky.

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Re: Extruder Calibration

Postby Eaglezsoar » Wed Mar 27, 2013 4:57 pm

Whats a sticky?

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Re: Extruder Calibration

Postby mhackney » Wed Mar 27, 2013 5:05 pm

keeps it at the top of the list of forum posts.

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Re: Extruder Calibration

Postby JakeCShake » Wed Mar 27, 2013 5:28 pm

Thanks Mhackney.....I believe this will be most helpful for a lot of users. Not to mention the input from others as things advance. Also, our thanks to Polygonhell for this VERY detailed calibration write-up!!!!!!!!! Job well done.......

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Re: Extruder Calibration

Postby MorbidSlowBurn » Wed Mar 27, 2013 6:06 pm

This is perfect. What needs to be done is all the posts about calibration and adjustments should be linked in a FAQ.

@mhackney your delta arm blues should also be a sticky.

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Re: Extruder Calibration

Postby mhackney » Wed Mar 27, 2013 7:51 pm

Only entire topics can be made sticky I think. What we can do is create a new post and copy-paste the info into that and I can then make it sticky. An index to these posts describing what they are and maybe a recommended sequence would be useful too.

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Re: Extruder Calibration

Postby cjdavis618 » Sat Mar 30, 2013 4:54 pm

mhackney wrote:Excellent writeup Polygonhell! I have to say, I was using an OLD version of slic3r and Protorface with my H-1s for the last year. I had them tuned to get very predictable and nice results. When I got the Rostock I needed/decided to get the latest and also use the Repetier host. There are a lot of differences in the latest slic3r and the earlier versions!

One sanity check for calibrating and checking calibration of extrusion is to calculate volume in and volume out. I made a little spreadsheet to do this. I've attached a copy here if anyone is interested.

ExtrusionCalculator.xls


Basically, once you determine your filament diameter and have calibrated steps-per, you tell the extruder to extrude 10mm (or whatever) into air so the filament hangs straight down. Then, you let it cool and snap off. Measure it's diameter and plug that into the spreadsheet. The spreadsheet calculates the volume of the input material and the volume of the extruded material. These should be relatively close in a well calibrated extruder. It is surprisingly useful. For instance, when I first setup my Rostock I used the defaults in the firmware for steps-per. I did a 10mm extrusion and discovered that the volume out was 1/2 what it should have been! That led me to discover/realize that the newer RAMBo ver 1.1 has 16 microstep by default!

@highcooley - calipers are not the best tool for measuring diameters for precisely the reason you mention - the amount of pressure you apply affects the measurement. A better tool is a micrometer. It has a mechanism that guarantees the same pressure is used for all measurements. Calipers are generally useful tools for a lot of applications and measuring hard materials like aluminum, they are not too bad. But measuring the diameter of soft materials like ABS or PLA they lead to the irreproducibility you've experienced.


So in this post, you said that the extrusion calculation needs to be "Close" to the amount fed into the extruder. So I guess to help make sense of this. How close does it need to be? I am using a digital micrometer on this so there is not any variation on the measurements except down at the sub micron level so readings are repeatable.

For instance, using the Default Extruder 1 settings in Polygonhell's firmware branch, My calculations for the spreadsheet, based on averaging the ABS filament both before the extruder and after extruded end up with totals like 24.05 fed in, and 22.98 out. Is that something that is close enough, or do I need to adjust steps to make them match further? If need to adjust, how close should they be?

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Re: Extruder Calibration

Postby mhackney » Sat Mar 30, 2013 5:05 pm

It isn't an exact science since the amount that actually gets extruded in a test like this can have some variation. But, if you are within 5% you should feel good about that. I've never seen the actual extruded filament be longer than the calculated length - probably due to some filament being retained, etc.

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Re: Extruder Calibration

Postby foshon » Sat Mar 30, 2013 10:43 pm

Eaglezsoar wrote:Whats a sticky?



Come on bro, like you don't know. Touch your keyboard.

Sorry couldn't resist.
Purple = sarcasm

Please do a board search before posting your question, many have been answered with very time consuming detail already.

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Re: Extruder Calibration

Postby foshon » Sat Mar 30, 2013 10:45 pm

mhackney wrote:Only entire topics can be made sticky I think. What we can do is create a new post and copy-paste the info into that and I can then make it sticky. An index to these posts describing what they are and maybe a recommended sequence would be useful too.



Make a topic, include links to clalibrations stuffs, and thne lock it so morons like me don't make references to sticky keyboards.
Purple = sarcasm

Please do a board search before posting your question, many have been answered with very time consuming detail already.

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Re: Extruder Calibration

Postby Eaglezsoar » Sun Mar 31, 2013 8:12 am

foshon wrote:
Eaglezsoar wrote:Whats a sticky?



Come on bro, like you don't know. Touch your keyboard.

Sorry couldn't resist.

HA HA :-)

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Re: Extruder Calibration

Postby harley573 » Mon Apr 01, 2013 8:32 pm

Okay, so I tweaked my settings as indicated and printed a cube, (see pics). It should be 20mm x 20mm x 10mm with .55mm walls. Actual is 19.05mm x 19.3mm x 9.7mm with .51mm walls.

I'm curious about a few things. For every print I've done, it has circled the part at least 1 lap and usually a lap and a half or more before it finally starts actually putting down plastic for the boundary.

Also, despite setting what I though was going to print 1 layer for the floor, it still printed two layers. It did 1 only for the walls, as expected.

One more thing. It didn't actually fuse the walls with the bottom layer in a few spots.

Thoughts? Input?
Attachments
20130401_184705.jpg
20130401_184634.jpg

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Re: Extruder Calibration

Postby harley573 » Mon Apr 01, 2013 8:38 pm

Additional photos:
Attachments
20130401_184837.jpg
20130401_184826.jpg

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Re: Extruder Calibration

Postby Polygonhell » Mon Apr 01, 2013 9:37 pm

Layer alignment looks good, IME printers tend to print slightly undersized.
You can adjust the X/Y size by changing the delta arm length in the firmware, I increased it slightly I think. Z ought to be spot on because it's direct translation of the belt motion.

The detaching could just be not printing quite hot enough, ABS in particular will delaminate if you print it 5 or 10 degrees too cold.

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Re: Extruder Calibration

Postby harley573 » Mon Apr 01, 2013 9:49 pm

I'm printing at 230°C with ABS. What do you use?

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Re: Extruder Calibration

Postby harley573 » Mon Apr 01, 2013 9:52 pm

My measurement in Z was .382 average. Should be .394 (10mm).

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Re: Extruder Calibration

Postby MorbidSlowBurn » Tue Apr 02, 2013 7:55 am

Harley- are you printing directly on the onyx? If so you will have difficulties leveling and getting a consistent zero. The onyx will warp under heating. So your vertical height will not be easy to dial in.

And is the 230C true temp or thermistor temp? I print about 230C nozzle temp measured with a thermocouple. Based on fans and how you assembled the hot end you may need to adjust.


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