Extrusin calibration

I think I am extruding a bit too much as holes etc. in my parts are slightly too small, and pins slightly big. The feed is correct (100mm feed is exactly 100mm of filament). I saw that there is a way to fine-tune the "extrusion multiplier" at [github.com]

I am stuck right near the start where it says, "Open the Gcode file and look for the value for perimeters extrusion width." I do not know where to look for that. I do not see a G code for extrusion width in the G-code Wiki (http://reprap.org/wiki/G-code). My Slic3r is set for "automatic" (0) on the default width (Printer settings/advanced).

I printed the bottom part of a cube with a single wall thickness and no infill and measured the walls with a calliper, and they are all 0.06mm thick, but I have no idea what they should be. I could experiment with different settings, but if there is a way to make a definitive measurement, I'd like to use it. Perhaps I could also change the default extrusion width from automatic to something else (perhaps 0.06), and see what I get?

Dave
(#106)

Hi Dave

Open the gcode you generate in a text editor, or upload to [gcode.ws]
At the start, it should say something like (this is from snowman.g):

; generated by Slic3r 0.9.10b on 2013-12-05 at 21:07:27

; layer_height = 0.24
; perimeters = 2
; top_solid_layers = 4
; bottom_solid_layers = 3
; fill_density = 0.4
; perimeter_speed = 20
; infill_speed = 20
; travel_speed = 60
; nozzle_diameter = 0.5
; filament_diameter = 1.75
; extrusion_multiplier = 1
; perimeters extrusion width = 0.85mm
; infill extrusion width = 0.87mm
; solid infill extrusion width = 0.85mm
; top infill extrusion width = 0.85mm
; first layer extrusion width = 0.48mm

G21 ; set units to millimeters

The '[something] extrusion width = ' lines are what you are looking for. These are set in Slic3r in 'Print settings > Advanced'. See: [manual.slic3r.org]

Slic3r tends to create quite fat default extrusion widths when set to automatic. At RRP, we generally set the extrusion width to the same size as the nozzle ie 0.5mm. Personally, I usually set it at nozzle size + 0.05mm, ie 0.55mm. The other limit is the layer height. Generally, you can't extrude a width that is less than 1.5 times the layer height, ie 0.4mm layer height, minimum extrusion width should be 0.6mm extrusion width. LOTS more here on the theory of extrusion width, layer heights, extrusion packing etc, on nophead's amazing blog (it got me started in repraps!): [hydraraptor.blogspot.co.uk]

When you know the extrusion width you have set, you can measure the part you print, and adjust the extruder multiplier until it is accurate. It is important that you are printing nice clean vertical walls (no wobbling in Z) or you're measured wall will be inaccurate.

Ian
RepRapPro tech support

Thanks droftarts. I meant 0.6mm not 0.06mm thickness. The G file states 0.5mm perimeter width, so I am over-extruding. Presumably I need to enter a factor of 0.83. I'll try that and re-print the hollow cube

OK, that appears to have done the trick. The hollow cube now has a wall thickness of 0.5mm as the G file states. I've printed out a new fan duct in ABS with that setting, and it was pretty much perfect, with the holes needing no filing. I am however a bit puzzled as to why I have needed such a large factor when nobody else appears to have this issue. As said, my extrusion length is calibrated accurately, and measuring the diameter of my filament shows that it varies between 1.75 and 1.77mm which would not account for such a large correction being needed.

If you're printing in ABS, read victors thread: [forums.reprap.org]
You'll need to print an x-carriage, nozzle-mount, z-runner-mount and extruder body (then the other extruder parts) as the heat will get to them eventually. If you're doing a lot of ABS, print all the printer parts in ABS.

Ian
RepRapPro tech support

I think the fan duct and nozzle duct parts have less problem, despite being very close to the bed, as cooler air is passing through them all the time. Though they will need changing too, eventually. With ABS, you could probably run with out the fan and nozzle duct completely, if you wanted, as ABS doesn't really need cooling as much as PLA does, when it prints - ABS extrudes a bit more 'sticky', less liquid, than PLA.

Ian
RepRapPro tech support

Quote
droftarts
If you're printing in ABS, read victors thread: [forums.reprap.org]
You'll need to print an x-carriage, nozzle-mount, z-runner-mount and extruder body (then the other extruder parts) as the heat will get to them eventually. If you're doing a lot of ABS, print all the printer parts in ABS.

Ian
RepRapPro tech support

Working on Sunday ???? Very much appreciated, Ian.

Yes, I've already replaced my X-carriage, nozzle mount and extruder mount with ABS, also the Z runner with the updated adjustable design. Next on the list is the fan housing and duct. I plan to replace all the parts with ABS over time even the ones not in the hot zone, if for no other reason than to keep it all one colour (I am printing my new Ormarod parts in black, mainly because that and white are the only colours I presently have).

I think my warping problem is solved, but I need to do some more prints to be sure. I think inaccurate temperature calibration was the main problem. I'm presently printing with extruder at 250, and bed at 100 for the first layer and 90 thereafter. I've found pipe solvent cement thinly squeegeed onto the glass bed (no Kapton) works best to adhere that critical first layer, with the Z zero height set just a tad low so the first layer is squished a bit. I may try dropping the extruder temperature, though if it is too low I've seen that even though the print looks OK, it is somewhat prone to delaminate.

Dave
(#106)

ABS isn't great at sticking to itself, unlike PLA. The hotter you can get it, before it becomes too hot and strings/sags, the better. Increasing the extrusion width, or decreasing the layer height, can help, as there is then more contact area. It might be an idea to block up the centre nozzle duct, so it doesn't get air immediately as it comes out the nozzle.

However, it also depends on the quality of the filament. Be aware that ABS is not the healthiest stuff to print, either. Ventilation, or an enclosed chamber with a vent going outside, is usually recommended.

(Another couple of things for the ABS printing guide).

As for working on Sunday... how else am I going to catch up with all the emails?! Just wait 'til I go skiing in a couple of weeks, and don't answer for 5 days...

Ian
RepRapPro tech support

Hmmm .. I've not got a great deal of ventilation when printing at home (too cold to have windows open!). I'll have to be careful. The smell is barely noticeable though. I prefer to print in ABS so that prototype parts for which the machine was bought to make are as close as possible in characteristic to the injection moulded ABS parts we will eventually be making for mass production. Some of the enclosures I'll be prototyping will house electronics that get quite warm. I've used prototypes from a laser & tank based 3D modelling machine before, but that's no good because the epoxy parts it makes are too brittle to allow the use of self-tapping screws in assembly so as to get a product that is as close as possible to the final mass-produced parts.

Hows the best way to check the extrusion width then, I see mention of a single thickness wall which I assume is 1 extrusion width where as from a CAD model we are working directly in mm. Is there a way to force it to do 1 travel round or is it best to run a model with 1mm thick walls and then calibrate from that?

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Regards

Chris H

Chris, see this link from the first post [github.com] . It has instructions to print a single walled object with no fill, though there are other ways to do it.

Ian
RepRapPro tech support

Quote
droftarts
I think the fan duct and nozzle duct parts have less problem, despite being very close to the bed, as cooler air is passing through them all the time. Though they will need changing too, eventually. With ABS, you could probably run with out the fan and nozzle duct completely, if you wanted, as ABS doesn't really need cooling as much as PLA does, when it prints - ABS extrudes a bit more 'sticky', less liquid, than PLA.

Ian
RepRapPro tech support

Don't you still need the heatsink and fan to prevent the filament melting too far up the nozzle? Or is that only for PLA?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
Don't you still need the heatsink and fan to prevent the filament melting too far up the nozzle? Or is that only for PLA?

I think Ian means that the middle outlet duct at the bottom could be blocked so it doesn't cool the extruded filament as it exits the nozzle, but cooling is still needed for the heatsink as far as I am aware.

Yes, sorry, I mean you could run without the 'fan duct' and the 'nozzle duct' printed parts. You still need the 12V fan on the heatsink, of course.

Ian
RepRapPro tech support